Ocular health assessment

7.1.1

The evidence base: When and how to assess the anterior segment and adnexa

This is typically performed during most full oculo-visual assessments and contact lens assessments and some partial oculo-visual assessments, plus before and after any procedure that touches the eye, such as tonometry and gonioscopy, to determine any iatrogenic damage. Certain symptoms and other case history information would lead to specific procedures being used and specific areas being assessed in more detail. For example, ‘acute flashes and floaters’ would lead to the assessment of the anterior vitreous for Shafer’s sign; ‘ocular foreign body’ symptoms might lead to ocular surface staining with fluorescein and lissamine green and lid eversion; gradual onset blurred vision plus problems with glare in an older patient suggests a careful assessment of the lens for cataract; a history of previous ocular disease/surgery would suggest searching for keratic precipitates after iritis and posterior capsular remnants after cataract surgery; a history of certain recurring diseases, such as trichiasis, corneal erosion, and blepharitis, suggests you search for these conditions again; some systemic medications can cause anterior segment changes: beta-blockers can cause dry eyes and long-term, high dosage oral corticosteroids can cause posterior subcapsular cataracts, etc.

Slit-lamp biomicroscopy, which is the current standard, offers excellent resolution, depth of field, control of a large range of illumination, and variable and high magnification (∼10× to 40×; involuntary eye movements reduce the clarity of highly magnified images and limit the value of increasing the magnification beyond 40×). The quality of the image is better in slit-lamp models that have higher optical quality lenses that use multi-aspheric lens designs and anti-reflection coatings. Patients who are obese or have neck or back problems may find positioning themselves at a table slit-lamp uncomfortable such that a hand-held slit-lamp may be preferred. Anterior segment optical coherence tomography (OCT) is becoming increasingly used to quantify some abnormalities, such as cells and flare in anterior uveitis ( section 7.1.3 , No. 7) and its use seems certain to increase further. Direct ophthalmoscopy, penlight, and loupe or Burton lamp assessment can be used when slit-lamp assessment cannot be undertaken, but they are very limited in resolution, illumination control, and magnification (∼2 to 4×).

7.1.2

Procedure for general slit-lamp examination

See video 7.1 for general slit-lamp examination. Familiarity with the adjustment controls of the slit-lamp is required. The positions of the controls differ for different models, but it should be possible to change the position, width, height, and intensity of the light beam and place filters over it ( Table 7.1 ); change the magnification of the biomicroscope and adjust its position in all directions; change the angle between the illumination and viewing systems and break the linkage between the these systems (decoupling), which allows focus on a point other than that being illuminated. Magnification is provided in one of three ways: a flip magnification system (the most basic with magnification typically provided at 10× and 16×), a rotating barrel, or a zoom continuous magnification (typically from 10× to 40×). Slit-lamps also differ in the degree of convergence of the microscope and clinician preference seems to vary depending on their own convergence stability.

• 1.

  Wash your hands thoroughly and clean the slit-lamp contact surfaces with an alcohol wipe in front of the patient.

• 2.

  Many clinicians will perform the slit-lamp examination without glasses because the field of view is greater the closer your eyes are to the slit-lamp eyepieces. If you have a high cylinder in your glasses, you may need to wear your correction to obtain adequate resolution.

• 3.

  Focus the eyepieces: Place the focusing rod in the appropriate holder, with the flat surface towards the viewing system. Switch on the illumination system to produce a slit-image on the focusing rod. Look through one eyepiece and turn it fully anti-clockwise; then, while viewing the focusing rod, turn the eyepiece clockwise until the slit-image on the rod is first in sharp focus. Repeat the procedure for the other eyepiece. The eyepiece should be set at approximately zero if you are an emmetrope or wearing your correction and set to your mean sphere correction (sphere + half of cylinder) if you are uncorrected. More minus/less plus might be required in younger practitioners due to proximal accommodation. Once you have each eyepiece focused, adjust the distance between the eyepieces so that the image is centred in the field of view of each eye. You should see a single clear image.

• 4.

  Seat the patient comfortably on a stable chair without rollers and ask the patient to remove any glasses. Explain the procedure in lay terms: “I am going to use this special microscope to carefully examine the front of your eyes.”

• 5.

  Adjust the height of the slit-lamp table so that the patient may lean forward comfortably and place their chin in the chin rest and forehead against the forehead rest. Adjust the chin rest so that the patient’s eyes are at an appropriate height to provide a large enough vertical range to allow adequate examination of the adnexa. Many slit-lamps have an eye alignment marker on a supporting beam of the headrest that should be level with the patient’s outer canthus. If your patient is obese, an exaggerated bend at their waist will often allow satisfactory positioning. Having the patient hold onto the handles (if available) can also be helpful.

• 6.

  Dim the room lights and ask the patient to look at your ear (your right ear for the patient’s right eye and your left ear for the patient’s left eye) or the instrument’s fixation device so that the patient’s gaze is straight ahead.

• 7.

  Use one hand to control the joystick (focusing and lateral/vertical movement) and the other to control the magnification and illumination and to manipulate the patient’s eyelids. Use a low rheostat setting for a wide, diffuse beam (for patient comfort) and a high rheostat setting for a narrower beam, or when filters are used, to give sufficient illumination.

• 8.

  There are several techniques that, with experience, you will use alternately or in combination to examine the anterior segment and adnexa thoroughly. A general procedure is to use diffuse illumination followed by a parallelepiped, which is described below. This is followed by descriptions of additional techniques with examples of when they might be used.

• 9.

  Diffuse illumination: Provides an overall assessment under low magnification (∼10×). Adjust the illumination to a wide beam and place a diffusing filter in front of it to systematically examine the components of the anterior segment and adnexa as described below.

• 10.

  Direct illumination using a parallelepiped: Use low to moderate magnification (∼10×) because magnification that is too high will result in missing obvious, moderately sized abnormalities. Set the illumination system at approximately 45° from the microscope position on the temporal side and use a beam width of approximately 2 mm. An illuminated block of corneal tissue in the shape of a parallelogram should be visible ( Fig. 7.1 ). A beam that is too narrow will make it difficult to detect abnormalities. Assess each of the structures described below in a systematic manner using the following procedure: Focus on the temporal tissue first with the illumination coming from the temporal side. Move the slit-lamp laterally across the tissue until the centre is reached, maintaining good focus at all times. Then sweep the illumination system across to the nasal side, taking care not to bump into the patient’s nose, and examine the nasal tissue. This scanning procedure may be repeated several times to examine all areas of the tissue concerned and may require more than one level of magnification. Being able to keep a parallelepiped sharply in focus as you scan from temporal limbus to central cornea and then nasal limbus to central cornea is the foundation for good slit-lamp technique.

  • (a)

    Eyelids and lashes: Examine the superior eyelid and lashes first using the scanning procedure described above. This can be easier with the patient’s eyes closed. Examine the inferior lid and lashes in the same manner, but with the patient’s eyes open, while also examining lid apposition to the eye and meibomian gland orifice appearance ( section 7.2.9 ). Assess the lid for anomalies, including an abnormal lid position (e.g., ptosis, entropion, ectropion), redness, inflammation, ulcers, and growths. Inspect the lashes for colour (e.g., white), areas where the lashes are missing or misdirected, and the presence of scales.

  • (b)

    Direct and indirect illumination: With increasing experience you will be able to look at both the area illuminated (direct illumination; see Fig. 7.1 ) and the area just outside the area of illumination (indirect illumination, Fig. 7.2 and see Fig. 8.18 ). Indirect illumination is used to view areas that become bleached with excessive light using direct illumination, such as fine blood vessels at the limbus, fine infiltrates or other opacities, and microcysts.

    

  • (c)

    Conjunctiva: Ask the patient to look upwards while you pull the lower eyelid gently downwards to expose the lower fornix for examination. Examine both the bulbar and palpebral conjunctiva using a scanning process. Next ask the patient to look downwards and gently pull up the upper eyelid, thereby exposing the superior bulbar conjunctiva for examination. Finally ask the patient to look in right and then left gaze to allow examination of the entire conjunctiva, plica, and the caruncle.

  • (d)

    Cornea and tear film: Use the scanning process to examine the cornea in three sweeps: inferior, central, and superior. Examine the inferior cornea by having the patient look up and the superior cornea by having the patient look down while holding up the upper eyelid. It can be useful to assess the tear film after a blink and note the quantity and type of debris if any. You can increase the width of the section of stroma seen by increasing the angle between the microscope and illumination system. You can obtain greater detail by increasing the magnification.

  • (e)

    Assessment of the tear meniscus: The height of the tear meniscus can be estimated by decreasing the height of the slit-lamp beam to 1 mm (or smaller) and then judging the relative height of the meniscus at the lower lid margin as a proportion of the beam height. Use a low to moderate illumination and a medium beam width and assess the meniscus more than two seconds after a blink and before tear break-up and reflex tearing become issues.

  • (f)

    Iris: Examine the iris with direct illumination by moving the joystick towards the patient. Use the scanning technique described above. Take note of the depth of the anterior chamber and the shape of the pupil.

  • (g)

    Lens: For a non-dilated pupil the illumination angle must be reduced until an optic section of the lens is just seen. This may be as small as 15° for an elderly patient with a small pupil. Further discussion of slit-lamp assessment of cataract with mydriasis is provided in section 8.4 .

  • (h)

    Anterior vitreous: Moving the joystick further towards the patient allows viewing of the anterior vitreous with a parallelepiped when the pupil is dilated. To look for anterior vitreous floaters ( Fig. 7.3 ), it can be useful to ask the patient to look up, look down, and then straight ahead, so that the opacities become visible as they float through the field of view (see video 8.1 ). Assessing the anterior vitreous for ‘tobacco dust’ (Shafer’s sign) is a specialised technique described in section 7.1.3 , No 6.

    

  

7.1.3

‘Specialised’ slit-lamp techniques

(See video 7.2 .)

If an abnormality/anomaly is suspected from the case history or detected during a routine slit-lamp examination, one or more of the following slit-lamp techniques may be used. With experience many or all techniques are used in quick succession. The slit-lamp magnification can be varied to examine the anomaly more carefully noting its size, shape, appearance, depth, and location.

1

Optic section

The illumination beam is narrowed and viewed at a wide angle to provide a cross-sectional view of the cornea and lens ( Fig. 7.4 ). It can be used to judge the depth of a foreign body in the cornea, whether a cataract is anterior or posterior cortical or subcapsular and is the technique used to grade nuclear cataract ( section 8.4 ; Fig. 7.5 ).

• 1.

  Set the illumination system at approximately 45° from the microscope and use approximately 10× magnification.

• 2.

  If the area of the cornea/lens you wish to view is temporal, place the illumination on the temporal side; if it is nasal, place it on the nasal side.

• 3.

  Narrow the beam to the narrowest possible width and sharply focus on the cornea/lens using the joystick. As you have greatly narrowed the beam, you need to increase the illumination using the rheostat.

• 4.

  A slice of the cornea and lens should now be visible (cornea, see Fig. 7.4 ; nuclear cataract, see Fig. 7.5 ). If the illumination system is temporal to the viewing system, the corneal epithelium or anterior lens will be on the temporal side of the image with the corneal endothelium or blurred posterior lens on the nasal side.

• 5.

  The section of the cornea can be broadened by increasing the angle between the microscope and illumination system. The focusing should be precise enough to allow the graininess of the stroma to be visualised.

• 6.

  To view the posterior lens, the joystick needs to be moved further forward and the angle of the illumination system may need to be reduced, depending on the pupil size.

• 7.

  Once the object of interest is identified, increase the magnification to obtain greater detail.

2

Specular reflection

Specular reflection is used to examine the endothelium for polymegathism (cell size variability) and pleomorphism (cell shape variability), the precorneal tear film, and variations in contour of the epithelium. When learning this technique, it is best to start by attempting to obtain an image of the anterior lens surface by specular reflection ( Fig. 7.6 ).

• 1.

  Set the illumination system at approximately 30° to 45° from the microscope, using a moderately wide 2 to 3 mm parallelepiped. Look through the eyepieces and focus the parallelepiped on the anterior lens.

• 2.

  Change the angle of illumination until the reflection of the instrument lamp is seen from the lens surface. This occurs when the angle of incidence equals the angle of reflection from the lens (see Fig. 7.6 a).

• 3.

  View the orange peel textural appearance of the anterior lens (see Fig. 7.6 b) to the side of the bright reflex.

• 4.

  To examine the tear film and epithelium, set the illumination system at approximately 45° to 60° from the microscope, using a moderately wide 2 to 3 mm parallelepiped. Look through the eyepieces and focus the parallelepiped on the cornea. Ask the patient to blink and use the particles floating in the tear film to help you focus.

• 5.

  Change the angle of illumination until a bright reflection is seen from the pre-corneal tear film. This occurs when the angle of incidence equals the angle of reflection from the cornea. This can also be obtained by moving the illumination/microscope system laterally until the two angles are equal.

• 6.

  To examine the endothelium, set the magnification to about 16× with a fairly wide 2 to 3 mm parallelepiped and initially focus on the tear film.

• 7.

  Alter the illumination angle and/or lateral position of the slit-lamp until the bright corneal reflexes (Purkinje images) fall on top of the corneal section. There should be two reflexes: on the epithelial side of the corneal section there should be a bright white reflex from the tear film (conjugate with the epithelium) and on the endothelial side a less bright, slightly yellowed reflex from the endothelium. You may need to alter the angle of illumination very slightly to separate the two reflections.

• 8.

  Increase the magnification to about 40× and move the joystick slightly forward to focus on the endothelium. If you then look to the side of the dull endothelial slightly yellowed reflex (nasal or temporal to the reflex, depending on the position of the illumination system), the duller picture of the endothelial hexagonal cells will be in view.

3

Retro-illumination from the iris

Retro-illumination from the iris ( Fig. 7.7 ) is used in the examination of corneal vessels, epithelial oedema, pigment deposits, or keratic precipitate on the endothelium and small scars on the cornea using light reflected from the iris. Opaque features appear dark against a light background.

• 1.

  Use a 1 to 2 mm parallelepiped with low magnification and set the illumination system to an angle of about 45°.

• 2.

  If it is possible to view the abnormality in direct illumination, bring it into focus and then lock the joystick position.

• 3.

  Decouple the illumination and viewing systems by loosening the knob at the back of the illumination system.

• 4.

  Direct the light onto the iris and view the structure against the light reflected from the iris. The magnification can be varied, as necessary.

4

Retro-illumination from the fundus

Retro-illumination from the fundus is used to examine cataracts and iris disorders using light reflected from the fundus. Cortical ( Fig. 7.8 ; see Figs. 8.29 and 8.30 ) and posterior subcapsular cataracts ( Fig. 7.9 ; see Fig. 8.27 ) are seen as dark opacities against the red background glow from the fundus. Iris abnormalities, such as peripheral iridotomies and loss of pigment, are shown by the red fundal glow being seen through the iris (iris transillumination).

• 1.

  Use a 1 to 2 mm parallelepiped with low magnification and set the illumination system to an angle of 0°. Adjust the beam height to the height of the pupil.

• 2.

  Focus on the iris or lens, as appropriate.

• 3.

  You will only be able to focus the anterior or posterior part of the lens at any one time. You can gain an approximate focus on the anterior lens by focusing the iris. To focus the posterior lens, you will need to push the joystick forwards (towards the patient). To gain a retro-illumination image of the lens with an undilated small pupil, you may need to decouple the instrument slightly and alter the angle of illumination by a small amount.

• 4.

  Observe any illumination coming through the iris. Although lens opacities are best observed with the pupil dilated, iris transillumination is best observed before dilation.

5

Sclerotic scatter

Sclerotic scatter can be used to view iatrogenic damage due to novice contact tonometry or gonioscopy use, foreign bodies, scars, and central corneal clouding caused by rigid contact lens wear; it involves observing the cornea while the illumination is directed at the limbus. The light is totally internally reflected in a healthy cornea and creates a glowing halo of light where it escapes from the opposite limbus ( Fig. 7.10 ).

• 1.

  Turn off the room lights to keep the surrounding light levels as low as possible so you can observe subtle amounts of light scatter.

• 2.

  Set the magnification at about 10× and use a 1 to 2 mm slit at about 45°. Focus the central cornea by ensuring the particles in the tear film are focused. Asking the patient to blink will move the tear film debris making them easier to find. Lock the slit-lamp position to ensure the viewing system remains focused on the central cornea.

• 3.

  Decouple the illumination and viewing systems by loosening the knob at the back of the illumination system.

• 4.

  Move the illumination system onto the temporal limbus. Ideally, shorten the length of the slit because extra slit length can produce light scatter from the sclera that may reduce the visibility of subtle defects.

• 5.

  Although you can scan the cornea for areas of light scatter with the naked eye, it is preferable to view it using the decoupled slit-lamp viewing system.

7

Anterior chamber assessment for cells and flare

Anterior chamber assessment is used to look for the signs of inflammation caused by uveitis of flare (protein) or cells (white blood cells) in the anterior chamber ( Fig. 7.12 ).

• 1.

  Turn off all the room lights and close your own eyes for a few minutes to start to dark-adapt.

• 2.

  Set the illumination system at approximately 45° from the microscope using moderate magnification (∼16×). Avoid having the light on the iris as well as specular reflection from the tear film because these conditions are likely to decrease dark adaptation.

• 3.

  Assess the anterior chamber for cells and flare using a parallelepiped and moderate to high magnification and brightest beam intensity.

• 4.

  To grade the cells and flare using the Standardization of Uveitis Nomenclature (SUN) classification narrow the height and width of the beam to obtain a beam 1 mm by 1 mm in size. Move the beam to the centre of the pupil and focus in the anterior chamber midway between the anterior surface of the crystalline lens and the posterior surface of the cornea. Focusing forward and backward within the anterior chamber will facilitate the viewing of cells. Note that the convection currents in the anterior chamber will cause any cells to rise where it is warmer (near the iris) and fall where it is cooler (near the cornea).

• 5.

  Count cells and grade the degree of obscuration of the iris details (see recording in section 7.1.4 ).

7.1.4

Recording of slit-lamp findings

Normal appearance: If no abnormalities are detected, record ‘clear’ if the tissue is transparent, such as the cornea and lens. Otherwise record ‘within normal limits’ (WNL) or equivalent.

Specific chief complaints: If the patient has a presenting complaint that could suggest an anterior segment abnormality and no abnormalities are detected, your recording should be more detailed to highlight that your examination was full and appropriate. For example, for a patient complaining of a foreign body (FB) sensation, you might record ‘cornea clear, no FB found, no trichiasis, no fl. (fluorescein) staining, no infiltrates, no ulcers, lids everted—all clear, no papillae,’ or similar. A patient with acute-onset flashes and floaters should have the results of a Shafer’s sign test recorded.

Any normal variation in appearance should be recorded (e.g., melanosis, concretions, corneal arcus, pingueculae, Mittendorf dot, vitreous floater, iris naevi, iris heterochromia, see sections 8.1 and 8.2 ) and imaged if appropriate.

Anomalies/abnormalities: Take a digital image of any abnormalities/anomalies, if possible, and/or use grading scales to record fluorescein staining, corneal oedema, conjunctival anomalies (papillae, follicles), injection, vascularisation, and forth. Record the size, shape, appearance, and location of other anomalies using a diagram and written description.

Cataracts: Image cortical and subcapsular cataracts using retro-illumination (see Figs. 7.8 and 7.9 ), otherwise draw them ( Fig. 7.14 ). If there are cortical opacities in both the anterior and posterior cortex, both should be imaged and recorded. Image nuclear cataracts using optical sections (see Fig. 7.5 ), otherwise nuclear yellowing and opacification can be graded separately using a cataract grading system, such as the LOCS III in which a photograph of the cataract is graded on a decimal scale against standardised colour photographs.

Cells and flare: Cells in the anterior chamber are graded (see Fig. 7.12 ) according to the number observed with grade 0 = < 1 cell, 0.5+ = 1–5 cells, 1+ = 6–15 cells, 2+ = 16–25 cells, 3+ = 26–50 cells, and 4+ = >50 cells. Aqueous flare is graded from 0–4+ depending on the visibility of the iris detail, with grade 0 = no flare, grade 1+ = faint flare, 2+ = moderate (iris and lens details remain clear), 3+ = marked (iris and lens details are hazy), and 4+ = intense (fibrous or plastic aqueous).

7.1.5

Interpretation of slit-lamp findings

A good understanding of the normal anatomy and physiology of the anterior segment, variations in normal appearance ( sections 8.1 and 8.3 ), the normal changes expected with age ( sections 8.2 and 8.4 ), and anterior segment disease is required. You need to consider whether any significant findings of slit-lamp assessments helped in your differential diagnosis of any pertinent symptoms and signs and whether they lead to a final diagnosis or an indication of the need for further testing.

7.1.6

Most common errors when using a slit-lamp

• 1.

  Poor positioning of the patient so that they are not able to maintain their forehead against the headrest, resulting in the image going in and out of focus.

• 2.

  Not focusing the eyepieces to compensate for your refractive error.

• 3.

  Not increasing the brightness when narrowing the beam or using a filter.

• 4.

  Not maintaining a sharp focus as the beam is swept across the eye.

• 5.

  Not developing a smooth, logical routine that can be repeated.

• 6.

  Using an optic section with high magnification and low illumination during the initial phases of the assessment.

• 7.

  Not examining the superior cornea and conjunctiva by having the patient look down and raising the upper eyelid.

7.2.1

The evidence base: When and how to assess the tear film and ocular surface

The tear film, which is assessed during slit-lamp examination, is specifically indicated in patients with any symptoms of an ocular surface condition and particularly dry eye disease (DED). DED is a multifactorial disease diagnosed by characteristic ocular symptoms and a loss of homeostasis of the tear film, and signs and symptoms are more likely when the tear film and ocular surface homeostasis is under stress ( section 7.2.2 ). Specific diagnostic indicators from the Tear Film and Ocular Surface Society (TFOS) dry eye workshop II (DEWS II) are a positive symptom score plus one of the three markers of abnormal homeostasis (tear film instability, ocular surface damage, and osmolarity), In addition, assessments of tear volume and meibomian gland structure and function can identify the aqueous deficiency and evaporative elements of DED, respectively, to help differentiate DED subtypes and determine correct management. Tests are being developed at a rapid rate, and this is an area that particularly requires regular attention to the literature.

Tear film instability is measured by the time taken for the tear film to break up after a blink. It can be measured invasively with fluorescein tear film break-up time (FBUT) or non-invasively (NIBUT) and both are simple, quick measurements. Fluorescein reduces the stability of the tear film and FBUT shows a wide variability in patients with mild and moderate DED, so that its usefulness seems limited. However, it is very widely used and perhaps for that reason, it is included in the DEWS II DED diagnostic test battery. NIBUT has the inherent advantage of not altering the tear film before measurements are taken and is thus preferred by DEWS II. ^,

Ocular surface damage is best assessed using a combination of the vital dyes fluorescein and lissamine green. Fluorescein is the standard dye for assessment of corneal surface damage, because it is taken up by damaged cells, adheres to the surface of cells and pools in depressed areas of the ocular surface. Lissamine green stains dead and devitalised cells and mucin, with staining properties that are similar to rose bengal, but with significantly less toxicity and discomfort, so that it has largely replaced rose bengal in clinical use. Both dyes are important for viewing conjunctival damage, including bulbar, tarsal, and lid margin. Lissamine green is particularly useful in highlighting lid wiper epitheliopathy, which is damage to the lid wiper region ( Fig. 7.15 ) that is responsible for spreading the tear film during blinks.

Increased tear film osmolarity has been shown to have a central role in the pathophysiology of DED. However, measurements of tear film osmolarity have been reported to be highly variable, particularly those provided by the iPen system. ^, Although the TearLab device has been shown to provide more reliable and accurate measurements, others have reported that 28% of TearLab scores from patients without DED give osmolarity values above the standard cut-off of 308 mOsm/L, which suggests poor validity of results. However, Nolfi and Caffery provide an alternative view that such scores are valid and indicate an unstable ocular surface before traditional clinical signs have revealed DED.

Tear volume helps to determine the relative contribution of aqueous deficiency DED and contributes to the diagnosis of Sjögren syndrome. Reduced tear volume increases the osmolarity of the tear film and produces friction between the lid wiper and the ocular surface, both of which contribute to ocular surface inflammation. ^, Although the components of aqueous deficiency and evaporative DED are on a continuum in many patients, the identification of aqueous deficiency can alter management strategies, such as the use of lacrimal occlusion earlier in the treatment paradigm, for example. The clinical assessment of tear volume may be undertaken using meniscometry, phenol red thread test, SM-tube (strip meniscometry tube), and Schirmer test. Meniscometry using the slit-lamp shows poor inter-visit repeatability due to poor visualisation of the meniscus (without the introduction of fluorescein), and variables such as time after a blink, location of measurement, environment (e.g., temperature and humidity), and illumination (part of section 7.1.2 ). Many commercial instruments are introducing imaging software to try to quantify the tear meniscus, but normative values and direct comparisons between instruments are not yet available. Clinicians with access to an OCT with anterior segment functionality can capture a repeatable measure of the tear meniscus height or area using a line scan ( section 7.11.1 ) that has been shown to correlate with Schirmer, FBUT, and symptoms. The Phenol red thread test is tolerated well by patients owing to the relative comfort of the test and short duration; it also provides good intra-visit repeatability. It appears to provide an indirect but realistic measurement of the tear volume and is helpful in differentiating aqueous deficient and evaporative causes of DED. The strip-meniscometry (SM) tube is a relatively new test that involves touching a strip impregnated with blue dye with the tear meniscus for 5 seconds. On its own, it provides poor specificity for the diagnosis of aqueous deficiency, but is much improved when combined with FBUT. The Schirmer test is typically used with the Ocular Staining Score (OSS) in the diagnosis of Sjögren syndrome, but is less widely used with other DED owing to its relatively lengthy test time, discomfort, and somewhat limited reliability and validity.

7.2.2

Symptoms assessment

A three-step process for symptoms assessment is proposed:

• 1.

  Any patient reporting symptoms indicative of DED in the chief complaint of the case history should undergo a full DED assessment. Symptoms typically include irritation, dryness, grittiness, foreign body sensation, burning, stinging, pain, tearing, contact lens intolerance, and transient blurred vision; less commonly mentioned symptoms include haloes around lights (especially at night), excessive tearing, stringy mucus discharge, redness, photophobia, itching, and asthenopia.

• 2.

  Patients at risk of DED should be identified in the case history. Risk factors include :

  • (a)

    Contact lens wear

  • (b)

    Post refractive or cataract surgery

  • (c)

    Occupations/hobbies that include extended concentrated tasks that reduce the blink rate, such as prolonged reading, viewing screens, or driving

  • (d)

    Occupations/hobbies associated with environmental factors that can exacerbate DED, such as wind, air conditioning, airline travel, low humidity indoors in winter months

  • (e)

    Cigarette smoking

  • (f)

    Systemic medications, including but not limited to beta-blockers, antihistamines, oral contraceptives, and acne medications.

Patients identified as at risk of DED from the case history or other elements of the eye examination should be asked a four-item set of ‘DED screening’ questions :

• “Do your eyes feel uncomfortable?”

• “Do you have watery eyes?”

• “Does your vision fluctuate, especially in a dry environment?”

• “Do you use eye drops?”

If the patent responds positively to any of the four questions, then ask “Do you have dry mouth?” to screen for Sjögren syndrome.

• 3.

  An essential component of DED diagnosis is a symptom assessment questionnaire such as the OSDI (Ocular Surface Disease Index) and the DEQ-5 (Dry Eye Questionnaire-5). Links to both questionnaires, as well as others, and their scoring systems are available online.

7.2.3

Non-invasive tear film (NIBUT) procedures

A video clip of the NIBUT procedure and many other of the diagnostic tests described here are provided on the TFOS DEWS II website ( www.tearfilm.org ).

NIBUT or tear thinning time measurements involve projecting a pattern on to the tear film and observing the specular image. Keratometer mires may be used in clinical practice, but grids are also available: the tearscope is a commercially available test for measuring NIBUT and many corneal topographers ( section 5.4 ) have a NIBUT module.

• 1.

  The illumination of the room should be low to provide the best image contrast.

• 2.

  With the patient’s head in position on the chin rest, focus the instrument so that a clear view of the pattern is seen. If using a keratometer, the mires should be centrally positioned and sharply in focus.

• 3.

  Instruct the patient to blink fully and normally three times, and then to hold their eye wide open and not blink until instructed.

• 4.

  Record the time between the last complete blink and the first indication of pattern break-up.

• 5.

  Repeat the measurement two more times and take an average.

7.2.4

Procedure for tear film osmolarity testing

A variety of instruments are commercially available and their measurement procedures are well described in the instrument manuals. In addition, a video clip of the TearLab instrument procedure is available on the TFOS DEWS II website ( www.tearfilm.org ) and is summarised below.

• 1.

  Ensure the TearLab is calibrated as directed in the user manual.

• 2.

  Explain the purpose of the procedure to the patient: “This test determines how concentrated your tears are and will help us determine whether you have dry eye and how we can best treat it if you do.”

• 3.

  Remove a TearLab pen from the reader station and insert a single use test card. Remove the protective cover from the test card.

• 4.

  With the patient looking up and away, gently touch the tear meniscus above the temporal lower lid next to the lateral canthus area ( Fig. 7.16 ; no significant pressure needs to be applied). After the tear sample has successfully been collected via passive capillary action the pen will beep. Note : Do not collect tear fluid within 2 hours of any topical eye drops being applied. It should be performed before any fluorescein is instilled or slit-lamp examination has been conducted.

  

• 5.

  Each test card will have a code number. Enter the code after docking the pen into the reading station. After following instructions, the osmolarity reading will be displayed.

• 6.

  Perform steps 3 through 5 on the other eye with a fresh single-use test card.

7.2.5

Procedure for phenol red thread test

• 1.

  The test may stimulate some degree of reflex tearing and should be undertaken prior to manipulation of the eyelids or to instillation of any fluid or dye into the tear film.

• 2.

  Lower the room lights. Instruct the patient to look up slightly and blink normally during the test.

• 3.

  Remove the threads by gently peeling the plastic film covering from the unsealed end of the aluminium sheet. Make sure that the folded 3 mm end of the thread is bent open at an angle that allows for easy placement onto the palpebral conjunctiva ( Fig. 7.17 a).

  

• 4.

  Pull the lower eyelid away from the globe slightly and place the folded 3 mm portion of the thread on the palpebral conjunctival junction, approximately one-third of the distance from the lateral canthus of the lower eyelid with the eye in the primary position.

• 5.

  Begin timing as soon as the thread touches the tear layer (see Fig. 7.17 b).

• 6.

  After 15 seconds, gently remove the thread.

• 7.

  Measure the length of the red portion of the thread in millimetres from the very tip (ignoring the fold; Fig. 7.18 ).

  

• 8.

  Because tear volume can vary, reliability can be improved by repeating the test on different days. It may also be helpful to ask the patient if they could feel the thread during testing, because it could be indicative of a reflex tearing component to the measurement. Excessively high measures (approaching 30 mm+) should be repeated.

7.2.6

Procedure for schirmer tear test

• 1.

  The test may stimulate some degree of reflex tearing and should be undertaken prior to manipulation of the eyelids or to instillation of any fluid or dye into the tear film.

• 2.

  Bend the round wick end of the test strips at the notch approximately 120° before opening the sterile pouch. Peel back the pouch and remove the strips. Only handle the strips by the non-wick ends to avoid contamination.

• 3.

  Have the patient look up and gently pull the lower eyelid down temporally. Place the bent hooked end of the strip at the junction of the temporal and central third of the lower eyelid margin ( Fig. 7.19 a). The strip should not touch the cornea when the eyelid is released (see Fig. 7.19 b). Release the eyelid and have the patient continue to look up, blinking normally. The patient can close their eyes if this is more comfortable, but should not squeeze the eyes shut. Both eyes should be measured at the same time.

  

• 4.

  Note the time of insertion. Remove the strip after 5 minutes or when it is completely wet, whichever comes first. Measure the wetted portion of the strip from the notch towards the flat end in millimetres and record this value.

7.2.7

Procedure for fluorescein tear film break-up time

(See video 7.4 .)

Topical anaesthetics should not be used prior to the test.

• 1.

  Fluorescein instillation: Wet the tip of a fluorescein strip with sterile saline solution. Be careful not to contaminate the saline by touching the strip to the tip of the bottle. Shake excess fluid from the strip over a sink (too much fluid will delay the time to maximum fluorescence and may drip onto and stain the patient’s lids and cheeks).

• 2.

  Ask the patient to look up and touch the strip to the inferior bulbar or tarsal conjunctiva, being careful not to touch the cornea. Do not use a sweeping movement to ‘paint’ the conjunctiva because it can provide too much fluorescein and create unnecessary discomfort for the patient. The strip can also be touched to the upper bulbar conjunctiva, but this has the disadvantage that if the patient blinks or attempts to blink, the eye will rotate and the strip may scratch the superior cornea. Ask the patient to blink several times to allow the fluorescein to spread across the cornea. Remove any excess fluorescein using a tissue and be careful not to spill the dye on the patient’s face or clothing as a stain will result.

• 3.

  Warn the patient that they may note colour if they blow their nose due to drainage through the nasolacrimal system.

• 4.

  Soft contact lens wearers can replace their lenses after a biomicroscopic investigation using fluorescein as long as the dye is irrigated out of the eye using saline prior to lens reinsertion. Otherwise irrigation is not necessary.

• 5.

  Measure FBUT 1 to 3 minutes after fluorescein instillation.

• 6.

  Examine the tear film at the slit-lamp with a wide 2 to 3 mm parallelepiped and low magnification. Switch to the cobalt blue filter so that the tear film should appear as a fine green film due to the fluorescein. The use of the Kodak Wratten yellow filter number 12 held over the observation system is helpful.

• 7.

  With the patient positioned at the biomicroscope, ask them to blink three times and then hold their eyes open without blinking until instructed.

• 8.

  From the time of the last blink, time how long it takes in seconds before dark spots or streaks appear in the even green tear film after a blink.

• 9.

  If the patient blinks before 10 seconds have passed, the measurement cannot be made and the procedure must be re-started.

• 10.

  Repeat the measurement two more times and take an average.

• 11.

  If the tear film breaks up immediately and consistently in the same location, there may be an epithelial basement membrane defect in that location on the cornea. The test should be repeated, not considering this defect, to get an indication of tear film stability.

7.2.8

Procedure for assessing ocular surface damage

Fluorescein is used to detect any corneal surface damage, and lissamine green is used to detect any interpalpebral bulbar conjunctival and/or lid margin damage. Both fluorescein and lissamine green dyes may be instilled at the same time, or in any order. Generally, clinicians use fluorescein first, then add lissamine, because they are using the fluorescein to also measure FBUT and the additional fluid of the lissamine green could alter FBUT measurements.

7.2.9

Meibomian gland evaluation

• 1.

  With the patient at the biomicroscope, use white light and medium magnification to inspect the lower eyelid margins.

• 2.

  Look for stenosis and closure of the meibomian gland orifices, thickened (inspissated) secretions, blocked glands, tear frothing on the eyelid margins, telangiectasias (‘spider veins’ because of their fine, web-like appearance) of lid margin vessels, notching of the Meibomian gland openings, and migration of these openings towards the posterior surface of the lids; all indicative of chronic disease.

• 3.

  Pull the lower eyelid down and look for concretions ( section 8.2.7 ) in the palpebral conjunctiva, as well as any inflamed, blocked, or missing glands.

• 4.

  Another method of assessing the meibomian gland function is to determine the position of the line of Marx, which is a clear line running along the lower lid margin, after fluorescein or lissamine green is instilled into the eye. In normal eyes this line is located on the conjunctival side of the meibomian gland orifices, and in meibomian gland dysfunction it is located on the cutaneous side of the orifices.

• 5.

  Slit-lamp examination only allows assessment of the meibomian gland orifices, but images of the glands can be taken using infrared light and several meibography imaging devices are available. The procedures of the various instruments are provided by the instrument manuals and are not provided here. The images provide clear evidence of meibomian gland changes ( Fig. 7.20 ).

  

7.2.10

Recording

Symptoms. Record the patient’s symptoms if part of their chief complaint as normal and indicate whether these symptoms only occur/are exacerbated under certain conditions (e.g., prolonged reading, airline travel, wind, contact lens wear). If the 4/5-item set of ‘DED screening’ questions were used, record both negative and positive responses. If a standardised questionnaire, such as OSDI, DEQ-5, was used, record as described within the instructions provided with each test.

Tear instability. The FBUT or NIBUT value should be recorded in seconds for each eye individually. Indicate the method that was used to determine this value. For example, NIBUT with grid pattern, RE: 10 s, LE: 12 s.

Ocular surface damage. A large number of grading and scoring systems exist for the documentation of ocular surface damage, with a variety of pros and cons. The grading scales used most commonly by optometrists are the CCLRU-Brien Holden Institute, original Efron, Johnson & Johnson (modified Efron), and Alcon scales. The scores of these scales should be accompanied by photographs and descriptions and drawings of any corneal and conjunctival staining patterns. Lid wiper epitheliopathy can be graded by the extent of staining as described in Table 7.2 .

Osmolarity. Record the instrument used and the osmolarity in mOsm/L (milliosmoles/litre).

Tear volume. Record the distance in millimetres that the thread is red (phenol red test) or that the strip is wet (Schirmer test) for each eye. For example:

• Schirmer: RE 8 mm; LE 5 mm in 5 minutes

• Phenol red thread: OD 12 mm; OS 15 mm in 15 seconds

Meibomian gland evaluation. Record any meibomian gland obstruction and dropout, lid margin telangiectasias, and expressibility of the glands. A ‘Meiboscore’ can also be used to grade meibomian gland dysfunction and the expressibility can be graded by the amount of pressure required to express the glands (1: light pressure, 2: moderate pressure, and 3: heavy pressure) and the quality of the expressed meibum (0: clear, 1: cloudy, 2: granular, and 3: toothpaste).

7.2.11

Interpretation

Symptoms. A score of 13 or more on the OSDI and 6 or more (and 12 or more for Sjögren syndrome) on the DEQ-5 are considered significant for DED. A detailed review of available questionnaires and their value is provided by Guillemin et al.

Tear instability. Normal NIBUT (keratometer or topographer) is between 28 and 60 seconds and a normal FBUT is between 15 and 45 seconds. NIBUTs and FBUTs of less than 10 seconds are indicative of an unstable tear film. Although FBUT measurements are significantly lower than NIBUT values, the disparity is smaller for short break-up times associated with poor tear quality. Normal FBUT and NIBUT measurements are sometimes limited by the patient’s ability to keep their eyes open and not blink.

Ocular surface damage. Surface damage on both the cornea (fluorescein) and conjunctiva (lissamine green) generally shows a characteristic distribution confined to the interpalpebral area of the ocular surface. Lissamine green staining is dose-dependent; therefore, if a very small amount is used the staining will be very minimal. Temporal and nasal interpalpebral bulbar conjunctival lissamine green staining is predictive of dry eye. More than five punctate fluorescein spots on the cornea is diagnostic of DED and more than nine punctate lissamine green spots on the conjunctiva is diagnostic of DED. Lid wiper epitheliopathy is diagnosed by staining greater than 2 mm and/or greater than 25% of the lid margin width (excluding Marx’s line).

Osmolarity. 308 mOsm/L is widely accepted as a cut-off value to help diagnose mild-moderate DED and an 8 mOsm/L difference between the eyes is indicative of a loss of homeostasis due to DED in the eye with the higher osmolarity. Further, this inter-eye variability has been shown to reduce with successful treatment of DED, making osmolarity measures important for monitoring treatment as well as diagnosis.

Tear volume. For the phenol red thread test, a measurement of <less than 10 mm wetting represents true dryness, whereas 10 to 20 mm wetting is considered borderline, and more than 20 mm is generally considered normal (see Fig. 7.18 ). Measurements in the high 20s or 30s are most likely caused by reflex tearing. For the Schirmer test, a measurement of 10 to 15 mm or more without anaesthesia is regarded as normal tear production. A value of less than 5 mm represents a significant aqueous dry eye. Several measurements should be made on repeated visits and averaged to obtain as accurate a result as possible.

Meibomian gland evaluation. The importance of evaluation of the meibomian glands cannot be over-emphasised given that obstructive meibomian gland dysfunction is significantly more common than previously understood (see Fig. 7.21 ). Digital (or other forms) expression should be utilised on evaluation of all lids (see Fig. 7.19 ). Poor expression may be due to gland atrophy or meibomian gland obstruction.

7.2.12

Most common errors

• 1.

  Touching the cornea with a fluorescein strip or wiping the fluoret against the conjunctiva, causing discomfort and reflex tearing.

• 2.

  Not obtaining a sharply focused image of the grid or mires before measuring NIBUT.

• 3.

  Performing the Phenol red thread or Schirmer test after manipulation of the lids, instillation of diagnostic drugs or dyes, or applanation tonometry.

7.3.1

The evidence base: When and how to assess the lacrimal drainage system

Patients who complain of excessive eye watering (epiphora) need assessing to determine whether this is caused by true nasolacrimal system obstruction or eyelid abnormality, such as ectropion (lower eyelid droops away from the eye) and eNtropion (eyelid turns iNward), or is caused by paradoxical reflex tearing associated with DED or other ocular surface problem. If nasolacrimal system obstruction is suspected, an assessment of the lacrimal drainage system is required. The dye disappearance test and/or the Jones 1 test helps to determine whether there is a stenosis (abnormal narrowing) or blockage of the nasolacrimal system. If the tests results suggest a stenosis or blockage, then dilation and irrigation of the system is indicated. Contraindications for dilation and irrigation include symptoms and signs of canaliculitis and dacryocystitis (including regurgitation of discharge from the punctum). Lacrimal sac palpation may help to determine if dilation and irrigation of the system are contraindicated. Dilation and irrigation itself may dislodge a concretion or mucous plug that has blocked the canaliculus. In this respect it is a therapeutic procedure. However, it is also a diagnostic procedure in that it helps to determine if the system is patent (open and unobstructed). Jones 2 testing, which attempts to determine the site of any blockage, is rarely used in primary eye care because if dilation and irrigation were unsuccessful the patient would likely be referred.

7.3.2

Procedure for fluorescein dye disappearance test

• 1.

  Explain the procedure and obtain informed consent. Encourage the patient to blink normally and not to squeeze the eyes during the procedure(s).

• 2.

  Ask the patient to blow their nose and clean it thoroughly with tissues.

• 3.

  Instil equal amounts of fluorescein in each eye and observe the patient for 5 minutes.

• 4.

  Compare the relative heights of the tear meniscus at the inferior margin of each eye and the degree of fluorescein spilling over the patient’s eyelids.

• 5.

  Do not allow the patient to blot the fluorescein because this might draw an excessive amount of fluorescein and tears out of the conjunctival sac. Wipe away any excess fluorescein dye that has spilled onto the patient’s cheek to avoid unnecessarily staining the skin.

7.3.3

Procedure for jones 1 or primary dye test

• 1.

  Moisten two to four fluorescein strips with sterile saline and touch to the inferior nasal palpebral conjunctiva, introducing a large amount of dye and fluid into the conjunctival sac. False test results are more likely if insufficient dye is applied.

• 2.

  Allow the patient to blink normally for 5 minutes. Ensure that fluorescein dye does not remain in contact with the facial skin long enough to dry.

• 3.

  Note that the dye disappearance test may be undertaken simultaneously with the Jones 1 test by observing the dye distribution and disappearance characteristics.

• 4.

  Instruct the patient to occlude the nostril on the unaffected side (if tearing problem is unilateral) or one nostril at a time (if tearing problem is bilateral) and blow into a white tissue.

• 5.

  Inspect the tissue for fluorescein using a Burton lamp or the cobalt blue light on the slit-lamp biomicroscope.

• 6.

  If no fluorescein is detected and especially if the dye was noted to have cleared from the eye other than over the lids onto the face, a false result may have been noted. Consider repeating the test or ask the patient to roll a sterile swab about 1 cm into the nose against the inferior turbinate. Check the swab for fluorescein with the cobalt blue light.

• 7.

  If fluorescein is recovered ( Fig. 7.23 a), no further tests are required as the nasolacrimal system is patent. Reflex tearing from DED and other causes should be reconsidered. Dilation and irrigation may still be considered if it is thought that there may be a partial blockage that might be relieved with irrigation.

  

• 8.

  If no fluorescein is recovered (see Fig. 7.23 b and c), there is either some degree of blockage of the drainage, there is a failure of the lacrimal pump mechanism, or a false test result was obtained, likely due to insufficient fluorescein being used.

• 9.

  Consider dilating the punctum on the affected side and repeating steps 1 to 5. If fluorescein is now recovered, the source of the poor drainage was likely stenosis of the punctum.

7.3.4

Procedure for dilation and irrigation

Dilation and irrigation are generally undertaken if no fluorescein is recovered with the Jones 1 test.

• 1.

  Prepare the instruments with appropriate disinfection of internal and external surfaces. Attach a reinforced 23-gauge cannula to a 3, 5, or 10 mL syringe.

• 2.

  Fill the syringe with 3 to 5 mL sterile saline. Push most of the saline through the cannula to thoroughly rinse the disinfectant, reserving approximately 1 mL for irrigation.

7.3.5

Recording of lacrimal drainage tests

Fluorescein dye disappearance: Record if the meniscus height is equal in each eye and if dye runs down over the patient’s cheek or disappears into the nasolacrimal drainage system. Relative speed of disappearance between the eyes is also relevant. Take note of the completeness of the blink, including apposition of the puncta, and the lid position.

Jones 1: Record whether or not dye was recovered on each side. Note that some sources label the presence or recovery of dye as ‘positive’ and absence of dye as ‘negative,’ so that a ‘positive Jones 1 test’ means that the system is patent. This is opposite to the usual convention of a positive test result being one that indicates a problem, so it is best to record whether or not dye is recovered in each test in order to avoid confusion (e.g., dye recovered in left nostril [left nasolacrimal system patent]).

Dilation and irrigation: Record whether or not the patient tasted salt or felt the solution in the throat. Also note if saline was regurgitated from the same canaliculus or from the contravertical canaliculus.

7.3.6

Interpretation of lacrimal drainage test results

Fluorescein dye disappearance: If the heights of the tear meniscus are unequal, it implies that the eye with the larger meniscus may have impaired tear drainage. It is less likely that there is a unilateral poor meniscus due to dry eye or unilateral pseudoepiphora from reflex tearing from the dry eye.

Jones 1: If fluorescein is recovered, no further tests are required as the nasolacrimal system is patent. However, some clinicians may consider dilation/irrigating if they feel there is a chance to dislodge a partial obstruction. If no dye is recovered, this indicates either a partial or full blockage in the system, a failure of the lacrimal pump mechanism, or it could be a false positive (likely due to insufficient fluorescein). If mucopurulent effluent is recovered, irrigation should not be attempted because there is an active infection/inflammation.

Dilation and irrigation: Normally fluid should exit from the system and be noted by the patient in the throat. A blocked system will offer resistance to fluid injection or cause regurgitation from the contravertical punctum. No fluid flow in the throat indicates a complete obstruction. Fluid subsequently noted in the throat indicates that the obstruction was relieved or there had been a partial obstruction or a stenosis.