The orthoptic assessment

Introduction

Orthoptists provide valuable information to the ophthalmology team about a patient’s binocular status and the integrity of the oculomotor system. Their examination validates subjective symptoms, confirms clinical diagnoses, and directs timing and type of management of binocular vision disorders. They are also able to implement non-surgical management modalities for strabismus and amblyopia.

This chapter outlines the components of the orthoptic assessment and highlights important aspects that are addressed by the orthoptist during such an evaluation.

Setting the Stage

An orthoptic assessment should be considered for any patient with known or suspected strabismus, or those with symptoms occurring in binocular conditions. Table 76.1 outlines the common indications for an orthoptic evaluation. The assessment should be tailored to each patient’s presentation.

Table 76.1

Indications for an orthoptic assessment

Indication	Objectives/Remarks
Motor system anomaly	Suspected: Confirm presence; classify type, e.g. comitant vs. incomitant Known: Generate evidence regarding etiological mechanism, e.g. innervational, mechanical, sensory forms Quantify control and size to help determine surgical plan Investigate and implement non-surgical management options, e.g. prisms, occlusion, utilization of head postures Diagnosis of sensory adaptations
Signs
Eyes appear misaligned	Rule out pseudostrabismus; if strabismus present correlate with presence or absence of symptoms
Eyes appear different sizes	Confirm globe or lid malposition
Lids at different heights	Confirm true vs. pseudo ptosis or lid retraction Confirm any associated motor anomaly, e.g.: Constant ptosis with CN3 palsy Variable ptosis with myasthenia gravis Lid retraction with thyroid orbitopathy
Pupil anomalies: Anisocoria/Light–near dissociation	Confirm and quantify Investigate for other associated features, e.g. ocular motility deficits, ptosis
Abnormal head posture	Confirm and quantify Determine if attributable to ophthalmological problem, e.g. vision advantage with null zone, elimination of diplopia or achieve binocular single vision with incomitant strabismus; occasionally to achieve monocular fixation in bilateral severe ocular motility restrictions; rarely due to skew deviation or mis-corrected/uncorrected refractive errors
Monocular eye closure	Elimination of second image or associated with intermittent exotropia
Symptoms
Eyes appear misaligned*	Confirm childhood onset with suppression/amblyopia; or acquired with significant monocular vision loss (unaware of second image)
Double vision	Confirm true binocular diplopia
Overlapping images	Distinguish monocular blur vs visual confusion or aniseikonia
Moving or shaking images	Confirm if oscillopsia and nystagmus
Eye strain/brow ache	Investigate for decompensating phoria
Changing clarity of binocular vision	Investigate for accommodative effort to control underlying deviationEvaluate refractive status
Unspecified binocular symptom	Full motor, sensory, and vision assessment – could involve each or all components; useful in patients unable to clearly articulate symptom
Unexplained vision loss (suspected malingering)	Confirm integrity of BV, e.g. document high-grade stereo acuity
New change in vision status	Investigate effect on binocularity when there has been a change in: Refractive status, e.g. refractive surgery, monovision Loss of vision, e.g. optic neuropathy, homonymous hemianopia Improvement in vision, e.g. removal of dense cataract, correction of long-standing aphakia Elucidate new symptoms arising from difference in image size (aniseikonia) or distortion of vision (metamorphopsia)
Visually immature patients
Detection of amblyogenic mechanisms	Investigate for the 3Ds – Deviated eye, Defocused eye, Deprived eye
Detection of amblyopia	Determine vision status and secondary effects on sensory status (lack of fusion) and motor status (strabismus due to lack of fusion)
Vision assessment in special populations	Infants, non-verbal, low vision, nystagmus. Also includes ADHD, autism, shy and timid, scared and aggressive, or those with severe motor deficits (CP)

ADHD, attention deficit hyperactivity disorder; BV, binocular vision; CN, cranial nerve; CP, cerebral palsy.

Orthoptists have expertise and contribute by:

understanding the relationship between efferent and afferent visual systems and their effects on binocular vision in the setting of anomalous function
identifying the main objective for each patient, e.g. chief complaint, goals, and desired outcome
rapidly constructing the best approach to the clinical investigation of strabismus and all disorders of binocular vision
ensuring key information is obtained efficiently and accurately
performing all specialized tests of binocular vision, and interpreting the results, to address the patient’s problems
formulating a diagnosis and/or differential diagnoses, implementing therapeutic modalities, and promptly communicating the clinical findings to the referring ophthalmologist.

Generally, the orthoptist’s examination room is 6 meters long. At that distance, strabismus measurements of the emmetropic or fully corrected patient are felt to be “free” of accommodation. The room should be large enough for the patient and one or two accompanying family members/caregiver, and it should be wheelchair-accessible. The room should be equipped with standard tests to allow a complete assessment. This includes adult and preverbal vision charts. An assortment of near and distance fixation targets to maintain the attention of younger patients should be available. Tests for the binocular status of a patient in free space, such as the Worth 4-dot test, Bagolini striated lenses, stereo acuity tests, and Maddox rods for torsion are all required. Loose prisms and prism bars are needed to measure strabismus. A direct ophthalmoscope, transilluminator, retinoscope, and wide aperture trial lenses for refraction are also needed.

Ideally, a synoptophore will be available. This device is used to investigate various aspects of binocular vision (e.g. suppression and fusion potential), and the size of the strabismus subjectively (including torsional deviations) and objectively in all gaze positions. Other specialized equipment includes Lees screen/Hess screen, Lancaster Red/Green test, and a perimeter to further quantify patterns of ocular motility defects and areas of binocular single vision.

The evaluation should be performed as accurately and efficiently as possible. This is particularly important with children whose tolerance of testing is often limited. The time required to complete the assessment is dictated by the complexity of the case, equipment available, and information necessary for that visit; generally more information is needed at the initial exam than for subsequent visits. While an orthoptist can detect and measure strabismus, assess ocular motility, and evaluate vision in 5–10 minutes, measurement of strabismus in all positions of gaze, full assessment of binocularity and retinal correspondence, accommodation, vergences, and investigation of non-surgical management modalities will take much longer, up to 45–90 minutes. Time allocation will need to take into account other individual patient requirements such as developmental delay, autism, or ADHD. Inquisitive patients/family members requiring lengthy explanations of tests and finding are other variables affecting exam duration.

Clinical Pearl

A key advantage of the orthoptist is their ability to independently design, administer, and interpret a comprehensive evaluation of binocular vision.

Beginning the assessment

Initial observations

The orthoptic assessment begins before the patient even sits in the examination chair. Watch the patient walk into the room, look for motor or coordination issues, facial or body asymmetry, or anomalous head posture. This is also the first opportunity to get a sense of the patient’s cooperation level that will be useful in determining the approach that will be taken. Table 76.2 provides examples of observations that should be made at this time.

Table 76.2

Initial observations prior to clinical testing

Items/Area	Feature	Potential information *
Disposition	Is the patient cheerful, upset, or shy?	Dictates approach needed to gain cooperation
Body	Gait abnormality	Possible cerebellar or neurological involvement – may suggest anomalies of smooth pursuit and saccades
	Obvious physical deformities	Previous trauma Developmental anomalies
	Neck/upper body anomaly	May prevent testing in all positions, e.g. PCT Avoid some tests, e.g. VOR
Head	Skull deformity	Plagiocephaly/craniosynostosis – orbital maldevelopment resulting in incomitant strabismus patterns
	Abnormal head posture	Nystagmus; incomitant strabismus
	Facial symmetry	Facial palsy; long standing CN4 palsy
	Wearing glasses	Refractive status; prismatic correction
	Hearing aids	Multisystem issues; need for accommodations during testing (speak louder)
Periocular	Scars, bruising	Orbital trauma – r/o incomitant strabismus
	Upward/downward slant of palpebral fissures	Orbit malformation – r/o incomitant strabismus
Lids	Malposition	Ptosis or lid retraction
Ocular	Nystagmus Globe malposition	Reduced vision; abnormal head posture Proptosis; enophthalmos; hypoglobus
	Chemosis	Orbital congestion; thyroid eye disease – r/o incomitant strabismus
	Irregularities of conjunctiva, cornea, iris, pupil	Ocular trauma or disease
	Anisocoria	Horner syndrome; CN3 palsy; physiological

CN, cranial nerve; PCT, prism cover test; r/o, rule out; VOR, vestibular–ocular reflex.

* Information limited to only a few points. Each feature can represent more issues.

Identify the main issues

History

A detailed history should be obtained from the patient. In the case of a child, an accompanying carer will contribute to build up a complete picture of the patient’s issues. Determine and list the main complaint and any other problem. When did this begin? Are the symptoms intermittent or constant? Has the patient received any treatment? Has the patient been compliant with this? Has it helped? Identify any coexisting ocular and medical conditions. Thorough questioning will help determine if the patient is presenting with an acute disorder, or a longstanding issue which is perhaps decompensating. The patient’s symptoms need to be explored in depth to help guide the rest of the examination. Table 76.1 summarizes common symptoms encountered in the orthoptic assessment.

Symptoms

Double vision, intermittent or constant, is one of the main presenting symptoms of the recent failure of binocularity, thus providing a clue to the onset of the strabismus. During the critical period of visual development, diplopia is easily overcome and abolished through the sensory adaption of suppression. Therefore, young children are often symptom-free despite the presence of strabismus. However, changes in vision or alignment can disrupt previously established mechanisms, and result in new symptoms of diplopia from longstanding strabismus. Improvement in vision, from refractive surgery, intraocular surgery or occlusion therapy can lead to a shift in fixation to the previously non-dominant eye and possibly lead to intermittent diplopia, e.g. fixation switch diplopia. A patient with well-established suppression from childhood strabismus may be symptomatic postoperatively if there is even a small degree of overcorrection in any gaze direction or if there is well-established abnormal retinal correspondence. In this way, like a detective, the orthoptist may need to tease out the cause of symptoms.

At times, what is perceived as double vision is actually not diplopia at all. The patient may be describing overlapping of images from visual confusion, rapidly alternating fixation causing repetitive shift of the image position, and monocular shadowing from lens opacities, macular degeneration, or dry eye. Alternatively, patients may present with symptoms other than diplopia that are still caused by a disruption in binocularity. Images that tend to suddenly appear, asthenopia, headaches and blurred vision can all be symptoms of decompensating or intermittent strabismus. Conversely, patients can present with diplopia and blur when there is no obvious strabismus. These symptoms can be due to visual acuity differences between the eyes which can be caused by incorrect refractive correction or induced prismatic effect in spectacle correction. Commonly, anomalies of convergence or accommodation such as insufficiency or excessive effort to overcome inadequate accommodation can cause these types of symptoms. The orthoptist will determine whether the patient’s symptoms are the result of disrupted binocularity or other ocular causes. Lastly, the cause of double vision may at first be obscure and only revealed by careful examination, such as the patient with symptomatic torsion.

Following a detailed history and consideration of the above situations, the orthoptist will begin to construct a best approach to rule in or rule out possible causes.

Determination of refractive status

After taking a detailed history, this is an ideal time to perform lensometry to determine the optical correction worn by the patient. Knowing the power of the glasses, any near correction, and/or presence of a prismatic correction (intended or unintended) is essential prior to testing. One should also determine the date and results of the last cycloplegic refraction. This information should be provided by the referring ophthalmologist for any new patient, or recorded in the medical record of a return patient.

Clinical Pearls

The orthoptic assessment is best performed after a complete ophthalmological exam and appropriate prescription of glasses that includes a period of refractive adaption with new optical corrections of moderate to large amounts.
Prism cover test measurements need to be performed:
- with and without incorporated prism in primary position, if present
- with and without optical correction in pre-presbyopic patients, e.g. accommodative esotropia
- through near correction in presbyopic patients, that includes the position most used by the patient, e.g. bifocals in a downgaze position, full framed readers/computer glasses in the primary position.
It is important to know the power of the optical correction worn versus the amount of the full cycloplegic refractive error:
- defines the borders for manipulating refractive power as a non-surgical management option
  - overminus and/or underplus for exodeviations
  - full plus in accommodative esotropia.
- optical penalization treatment in amblyopia.
High refractive errors, particularly anisometropia, will induce prismatic effect outside of primary position, altering the true size of a measured deviation.
Uncorrected anisometropia can produce different measurements when switching fixation from one eye to the other, leading to PCT measurement errors.

Gain cooperation

The beginning of the examination is the ideal time to build a good rapport with the patient. Gaining cooperation will influence the speed and complexity of testing that can be performed during the visit. This is always considered when dealing with toddlers; however, it is just as important to gain rapport with the child’s parents, and also with adult patients, to relieve any anxiety. It is also the time to get a sense of the patient’s ability to participate with subjective testing. The first few minutes will determine the best way to interact with the patient, e.g. how tests will be explained, what is the best volume to speak, awareness of gestures or actions that may startle the patient such as moving quickly, bringing things close to their face, etc. Making the necessary adjustments to the exam at this time will greatly increase the quality of the evaluation.

Clinical Pearls

The strategy is to convince a young patient they want to do the test, rather than asking if they want to do it.
Gaining trust can be achieved by providing a brief explanation of what to expect, e.g. “We are going to play lots of games and look at pictures!”
Remind them that nothing in your room is going to hurt them.
Give them your full attention. Make a point of talking with young patients and not just the parent. Always listen to what they are saying. It is surprising how often they mention issues that a parent was unaware of.

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