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Tinted Lenses
Introduction
Eye colour is universally recognized as an important and defining natural physical characteristic of the body human, and a contact lens is an effective vehicle for modifying or enhancing this appearance for those who wish to do so. More importantly, tints can be applied to contact lenses to help normalize the appearance of disfigured eyes and help improve vision in diseased eyes.
Tints have been applied to all forms of contact lenses since their invention over a century ago. In his original treatise in 1888, Fick clearly recognized the potential prosthetic benefits of contact lenses upon which opaque iris patterns and black pupils could be painted ( ). The inventor of the corneal lens, Kevin Tuohy, attempted to tint lenses, and Otto Wichterle, the inventor of the soft lens, was awarded two patents describing processes for tinting hydroxyethyl methacrylate (HEMA) lenses.
Despite the advanced technology currently being utilised for manufacturing tinted contact lenses, they are currently prescribed at very low levels (less than 2% of all lenses) in most markets ( ).
This chapter describes the various applications of tinted lenses and current technology used for lens tinting.
Basic Options
An important initial consideration in deciding on the most appropriate tinted lens for a given patient is whether to use a rigid or soft lens. A particular lens type may be indicated for clinical reasons; for example, a rigid lens would be required in the case of a sighted eye with corneal distortion.
In general, rigid lenses are well suited for prosthetic use due to their lifespan. An advantage of rigid lenses is that it is possible to paint unique designs and so effect a realistic iris appearance in terms of a more precise match of colour and iris features. A convincing cosmetic effect is difficult to achieve with a conventional rigid lens of, say 9.5 mm diameter, because it would not completely cover the cornea and iris, and move on blinking. These potential disadvantages can be obviated by fitting with a large diameter miniscleral lens. In certain cases of extensive ocular disfiguration, painted scleral lenses may give the best result. Soft lenses have the advantage of offering full corneal coverage and stability on the eye and are thus particularly suited for cosmetic use.
The applied tint can be translucent or opaque. The resulting lens may be wholly translucent if translucent tints alone are applied, semiopaque if opaque tints have been used on portions of the lens and completely opaque if opaque tints have been applied across the entire lens surface. A translucent tint allows certain wavelengths of light to pass through, thus effecting a colour change. Light passing through such a tint, and reflecting back off the iris, will be further modified such that the cosmetic effect is a combination of the colour of the translucent tint and the iris. Translucent tints can therefore be said to enhance or modify natural iris colours. This effect is successful only with relatively light-coloured irides.
Opaque tints can substantially or completely block the passage of light. A coloured pattern can be applied over a totally opaque base to effect a complete change of eye colour, while at the same time, for example, masking out underlying iris disfigurations. Thus the primary cosmetic application of opaque tints is to change the colour of dark irides or have the prosthetic effect of restoring a normal appearance to a disfigured eye.
Tinted Lens Designs and Applications
Translucent and opaque tints are applied to rigid or soft lenses for a variety of reasons, which are outlined below.
Handling Tint
A handling tint – also known as ‘lens visibility tint’ or ‘locator tint’ – is incorporated into soft lenses so that these lenses can be easily seen in the lens case or on a domestic surface if accidentally dropped ( Fig. 21.1 ). Such a tint is very light (between 5% and 15% absorption) and does not alter iris colour; however, it may make the lens slightly more visible on the eye by virtue of the handling tint being noticeable where the lens edge impinges over the sclera. A handling tint does not affect vision or colour perception. Some wearers find lens handling difficult as even with the pale handling tint the lenses can be hard to see. In those cases, a cosmetic tinted lens may be fitted to enable easier handling.
Cosmetic Tinted Lenses
A cosmetic tinted lens can be defined as a lens that is designed to beautify an otherwise normal appearance. This can amount to enhancing eye colour with translucent tints, modifying eye colour with a combination of translucent and opaque tints, or completely changing eye colour with opaque tints. Cosmetic tinted lenses are considered to be a fashion accessory, and as such they are often worn by emmetropes. Indeed, most tinted lenses are produced for their cosmetic effect ( Fig. 21.2 ). The most frequently used tints are aquamarine, blue, green and amber. As is the case with handling tints, cosmetic tints do not appreciably affect vision or colour perception ( ), although patients may report an initial transient effect. The light transmission through cosmetic tinted lenses is usually in the range 75%–85% ( ).
A more recently introduced concept in cosmetic lenses is the iris-enhancing ring or ‘Circle lens’. This is aimed at the Asian wearer, whose average horizontal visible iris diameter is 11.2 mm. The outer diameter of the limbal ring of the 1-Day Acuvue Define lens is 12.5 mm, thus enlarging the appearance of the eyes ( Fig. 21.3 ).
Prosthetic Tinted Lenses
A prosthetic tinted lens is designed to normalize an otherwise abnormal appearance. Providing the patient does not have unreasonable expectations, the lenses are generally satisfactory in terms of wearing time, comfort and colour ( ). Typical cases for which such lenses are indicated include aftermath of trauma, ocular disease and congenital abnormalities ( Fig. 21.4 ).
Visible deformities of the anterior ocular structures – in particular the cornea, iris and crystalline lens – can be effectively masked using dark ( ) or opaque ( ) tints. Specific tinting configurations can be tailored for different circumstances ( Fig. 21.5 ); examples include:
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a painted iris and clear pupil for a sighted eye with a disfigured iris;
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a painted iris and opaque pupil for a nonsighted eye; and
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a clear iris and opaque pupil for a nonsighted eye with a dense cataract.
Therapeutic Tinted Lenses
A therapeutic tinted lens can be defined as a lens that is designed to treat an underlying defect or disease. Primary therapeutic applications of tinted contact lenses include reducing excessive photophobia and glare due to a range of congenital or acquired conditions.
Achromatopsia
Several studies have shown that red tinted contact lenses may be useful in relieving the photophobia associated with a number of cone disorders, including achromatopsia ( ). Tinted lenses are particularly beneficial, since reducing the amount of light reaching the retina prevents rod saturation and minimizes glare and photophobia. Hydrogel contact lenses with a central red tinted portion were fitted to patients with a range of degenerative retinal diseases ( ). Most patients demonstrated improvement in binocular visual acuity as well as improvement in contrast sensitivity; all patients described a major improvement in their photophobia both outdoors and indoors, as well as a marked improvement in quality of life with the tinted contact lenses. The dark-tinted glasses with side-shields and floppy hats usually used to manage these conditions are very conspicuous and can cause marked psychological morbidity in children. fitted 70% brown contact lenses to children with stationary cone dystrophies and marked improvements in their quality of life were observed.
Albinism
Albinism is a group of genetic disorders where melanin production is impaired, resulting in the absence of pigmentation in the iris and retinal pigment epithelium. Both of these effects contribute to increased light transmission through the iris and more reflected light from the fundus. There may be cosmetic benefits from a tinted contact lens in albinism, refractive corrections can be incorporated, nystagmus may be reduced but primarily their use is to reduce photosensitivity. reviewed the history of contact lenses for visual rehabilitation in albinism, which dates back to 1930, when tinted scleral lenses were fitted that had an opaque backing to the haptic portion. Modern soft lenses with opaque iris printed designs have been used to good effect ( ).
Amblyopia
Opaque contact lenses have been used for occlusion therapy in amblyopia ( ) and prosthetic lenses have also been trialled for this purpose. The degree of penalization can be varied with different iris print patterns and opaque pupil sizes. Peripheral fusion can be preserved with some lenses ( ).
Aniridia
Aniridia is a bilateral autosomal dominant genetic disorder, which results in iris abnormalities. It may be corrected with tinted or iris printed contact lenses ( ; see Fig. 21.6 ). The lenses may improve cosmesis, reduce photophobia and reduce the higher-order aberrations associated with a large pupil. Care must be taken to monitor patients with aniridia who wear contact lenses due to their susceptibility to limbal stem cell failure. Cases with other pupil anomalies, such as iris coloboma or due to trauma, may similarly benefit from reduced glare, reduced higher-order aberrations and from the elimination of monocular polyopia.
A smart artificial iris encapsulated in a scleral lens has been developed, using guest-host liquid crystal cells, which is able to actively modify the transmittance of the lens and the effective pupil size. Preclinical testing suggests this should be beneficial in aniridia ( ). The artificial iris enables virtually all higher-order aberrations to be compensated with active control of the pupillary diameter occurring by activation of liquid crystal cells based on ambient lighting.
Bothnia Dystrophy
Dark-brown tinted lenses were shown to help patients with Bothnia dystrophy, a genetically defined retinal dystrophy with prolonged dark adaptation ( ). The patients with the lowest visual acuity described the most obvious improvement in visual function, this group of patients preferred darker contact lenses, with transmittance between 10% and 30% at 555 nm.
Diplopia
A tinted contact lens can be a useful alternative to a covered spectacle lens or eye patch when occluding one eye. reported on the use of occluding tinted contact lenses in cases of intractable binocular diplopia in strabismus, severe vision distortion or intolerable photophobia.
There are often secondary therapeutic benefits of tinted lenses designed for prosthetic use. These include the following examples: a lens with an opaque pupil masking a cataract but also eliminating disturbing light in a near-blind eye, a rigid lens with an opaque iris pattern fitted to a distorted cornea in a sighted eye also having the effect of improving vision by neutralizing corneal optics and the incorporation of appropriate lens power to correct vision, and a lens with an opaque iris pattern to mask aniridia in a sighted eye also reducing glare.
Performance-Enhancing Tinted Lenses
Colour Vision
Monocular prescription of red tinted lenses to enhance colour vision in colour-defective patients has long been advocated; however, their use is controversial. X-Chrom lenses have a dark red pupil, the diameter of which may be varied to suit individual needs. One eye receives a different luminance and chromatic signal from the other eye and through a process of retinal rivalry a wider range of colours can apparently be interpreted.
showed the ChromaGen lens significantly reduced Ishihara error rates, particularly for deutan subjects, but had no significant effect on Farnsworth lantern test performance. Similarly, reported similar findings for both light and dark red lenses; colour-defective patients wearing such lenses gave near-normal results on Ishihara plates but the FM100Hue test did not show any improvement with either tinted lens. There are medico-legal implications in prescribing these lenses to enable patients to pass the colour vision tests required in occupations with colour-vision-related restrictions. Nevertheless subsequent attempts have been made to produce contact lenses capable of managing colour vision deficiency using dyeing techniques ( ) and with gold nanoparticles ( ).
Dyslexia
Various tinted lenses have been devised to cure dyslexia and to alleviate migraine. These can also technically be described as therapeutic applications, although in most cases it appears that improvements are attributed to a placebo effect rather than a true therapeutic effect.
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