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.
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.
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:
a painted iris and clear pupil for a sighted eye with a disfigured iris;
a painted iris and opaque pupil for a nonsighted eye; and
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.
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 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 ( ).
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 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.
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.
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
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 ( ).
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.
Visual performance in multifocal contact lenses will often vary with pupil size. An attempt was made to determine if the use of neutral density filters incorporated into a contact lens could increase pupil size sufficiently in early presbyopia such that visual performance in a multifocal lens could be enhanced. Whilst enlarged pupil size could be achieved, distance vision was not improved. With a transmittance of 50%, vision and contrast sensitivity were degraded ( ).
Sport-tinted contact lenses have become available to athletes in an attempt to improve performance by enhancing contrast. Two shades are advocated for different sports. An amber tint is suggested for fast-moving ball sports such as football, rugby, tennis and baseball. A grey-green tint is suggested for golf, running and training. The now-discontinued Amber and Gray-Green Nike Maxsight lenses had 50% and 36% visible light transmission, respectively.
Although there may be statistically significant differences in contrast when sport-tinted contact lenses are worn, there does not appear to be evidence that the lenses provide any clinically significant difference when considering contrast enhancement ( ). However, it has been suggested ( ) that the Maxsight Amber and Gray-Green lenses provide better contrast discrimination in bright sunlight, better contrast discrimination when alternating between bright and shaded target conditions, better speed of visual recovery in bright sunlight and better overall visual performance in bright and shaded target conditions compared with clear lenses. These lenses are no longer produced.
investigated the impact of yellow and orange Wöhlk ‘Sport Contrast’ tinted contact lenses on colour discrimination using the Erlangen colour measurement system. Both lenses caused a shift of the reference colour towards higher-saturated colours. Colour discrimination ability with the yellow- and orange-coloured lenses was significantly enhanced along the blue-yellow axis, in comparison with the reference measurements without a tinted filter. Along the red-green axis only the orange lens caused a significant reduction of colour discrimination threshold distance to the reference colour. They concluded that yellow- and orange-tinted contact lenses enhance the ability of colour discrimination.
Prophylactic Tinted Lenses
The purpose of a prophylactic tint is to prevent injury or disease of the eye. The primary prophylactic application of tinted lenses is protection from excess ultraviolet (UV) light. Glare reduction can also be achieved with photochromic lenses.
Lenses with a UV protection filter or tint may be beneficial to lens wearers who are frequently exposed to UV radiation, such as those who:
pursue an active outdoors lifestyle, especially near snow, sand and sea;
work outdoors (such as professional tennis players);
use photosensitizing drugs;
are often exposed to artificial UV sources during work or recreation; and
Some argue that everyone can benefit from a UV-blocking tint to prevent chronic ocular damage. Nontinted lenses and lenses with standard cosmetic tints transmit light down to 230 nm and thus do not provide acceptable UV protection ( ). Lenses with special UV-blocking tints were found by to block light lower than about 350 nm from entering the eye, thus affording the desired protective effect. reported that the UV-blocking characteristics of five lenses evaluated performed equally well across the UV spectrum. measured the UV transmission spectra of 30 ‘UV protective’ contact lenses at 5 nm intervals between 290 and 400 nm and concluded that most lenses did not provide significant UV protection in the UV-A range. noted a statistically significant difference among four contact lenses tested for the visible, UV-B and UV-A portions of the spectrum.
The UV transmittance characteristics of a range of daily disposable and silicone hydrogel contact lenses were investigated by . They noted that even those contact lenses not incorporating a UV-blocking monomer still demonstrated some attenuation of the UV spectrum and can therefore also serve to reduce the amount of UV incident at the anterior ocular surface.
Patients must, however, be warned of the limitations of UV-blocking contact lenses. For example, solar keratitis can occur in exposed regions of the cornea in UV-blocking rigid lens wearers, and the conjunctiva is susceptible to solar damage in both soft and rigid lens wearers. Accordingly, patients should be advised to wear UV-protecting sunglasses or goggles during prolonged periods of UV exposure, and to protect exposed regions of skin in extreme conditions. Contact lenses may be the only form of UV protection possible in situations where spectacles cannot be worn, for example for sports such as surfing.
The first spectacle lenses with photochromic properties were developed in the 1960s. However, adapting the colour-changing technology to contact lenses was not successfully achieved until 2019 with the launch of ACUVUE OASYS With Transitions® Light Intelligent Technology™. These contact lenses contain a photochromic additive that adapts the amount of visible light filtered to the eye based on the amount of UV light to which they are exposed ( Fig. 21.7 ). This results in – darkened lenses in bright sunlight that automatically return to a slight tint when exposed to normal or dim lighting conditions. Due to the constant ocular temperature, activation happens quickly and consistently, irrespective of ambient temperature, unlike spectacle photochromic lenses. The lenses darken in less than a minute and fade back in around 90 seconds.
The photochromic molecules are polymerised uniformly throughout the senofilcon A material at a density that maintains an acceptable cosmetic outcome ( Fig. 21.8 ). A novel curing process was developed to ensure such lenses could be manufactured at scale.
Photochromic lenses may be prescribed for wearers wishing to benefit from glare reduction. Compared to performance with a nonphotochromic lens, photo-stress recovery time was faster, glare discomfort was reduced, glare disability lessened and improved chromatic contrast thresholds were demonstrated with the photochromic contact lens ( ).
Theatric Tinted Lenses
Lenses can be designed and tinted – typically with opaque agents – to create dramatic or theatrical effects. Such lenses are also known as ‘costume’ or ‘party’ lenses. Effects such as wolf eyes ( Fig. 21.9 ), national flags, hearts, stars and smiley faces can be created, and some companies market afocal lenses specifically for this purpose.