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) Trauma has resulted in partial aniridia, giving rise to an unsightly appearance and excess glare. (B) An opaque dot-matrix print soft lens offers the prosthetic advantage of an improved appearance and the therapeutic benefit of reducing excess glare.

(Courtesy H. J. Völker-Dieben, Bausch & Lomb Image Collection.)

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.

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.

Presbyopia

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

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.

Ultraviolet-Blocking Tint

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:

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  pursue an active outdoors lifestyle, especially near snow, sand and sea;

  
  
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  work outdoors (such as professional tennis players);

  
  
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  use photosensitizing drugs;

  
  
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  are often exposed to artificial UV sources during work or recreation; and

  
  
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  are aphakic.

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.

Photochromic Tint

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.

Transmission spectra of ACUVUE OASYS with Transitions for lens in fully activated (outdoor state) and inactive (indoor) state, compared to ACUVUE OASYS. *Calculated per ISA-8980-3 for 380–460 nm (blue light hazard function B (λ)).

(Courtesy Johnson & Johnson Vision Care.)

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.

Cosmetic appearance of the photochromic lens changes with ambient light.

(Courtesy Johnson & Johnson Vision Care.)

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 ( ).