By Bonita Lutzka
The primary function of contact lenses is obviously to improve vision. However, there are many instances where a contact lens can be used to alter the physical appearance of a patient. Prosthetic lenses need not only be fitted for cosmetic reasons to cover scarring, but the reason for fitting them can also be therapeutic, preventative or necessary to filter out light or block out all vision in some cases.
Some of the most common indications for prescribing a prosthetic lens are:
Occluded lens: To cover any kind of scarring or to get rid of diplopia (double vision) or for amblyopia (lazy eye) training.
Pinhole lens: To redirect light with a pinhole effect for patients with photophobia caused by aniridia, albinism or coloboma.
Filtered lens: To reduce glare and enhance contrast for patients with photophobia, migraine sufferers, colour deficiency, rod cone dystrophy and to enhanced vision for sports.
When a patient walks into an optometry practice with any of the above conditions it is important to consider the emotional state of the patient. In the initial consultation it is important to establish exactly what the patient’s expectations are. The patient will need to be told that a prosthetic lens will never duplicate their non-damaged eye exactly, but will be as close a match as possible. It is advisable to discuss all of the options available, this way the patient can feel part of the decision making. As soon as a patient is part of the decision making they understand the complexity and tend to be more accepting of the end result.
What the optometrist does
The optometrist will aim to get the best fitting lens in terms of centration and movement, given that there will be challenges presented by scarring and irregularities sometimes causing decentration. K-Readings are often not possible and if taken can be deceiving. It is advisable to establish tolerance early on, as there may well be hypersensitivity due to a damaged or abnormal cornea. This can be done using a clear disposable trial lens. Eighty percent of scarred eyes are successfully fitted with a lens with standard parameters (eg.: 8.60 base curve or an 8.70 base curve).
The Contact Lens Lab of SA has fitting sets available to assist with difficult fits. Options in design of these trial lenses include; reverse curves, prism ballasts and base colours with tinted or open pupils to assist in finalising the position of the iris to match the other eye. Where applicable, an over-refraction can also be done with the trial lens to see if any improvement is possible before doing the final artwork. If the lens is too tight or loose you can request the necessary set to obtain the best suited lens. If the lens is fitting well and stable but not centrally, one would need to use a prism ballast lens design to help with displacing the iris on the lens.
These lenses have different base curves and all have a weighted prism portion on the lens to help stop the lens from rotating. The final lens will sit off centre on the eye, but the iris will be positioned to make the patient’s straightforward gaze balanced in both eyes.
What the Contact Lens Laboratory does
A variety of different solutions are possible with custom made soft prosthetic lenses and when working directly with a laboratory that manufactures the lenses, as well as painting or tinting the prosthetics, the options are limitless. Good communication and understanding is the key to the best result.
Scarred eyes sometimes don’t have a uniform surface to fit a lens on. In these situations you can request the laboratory to make the final lens thicker to mask such irregularities or use a reverse curve lens design to help stabilise the lens centrally.
The aim in fitting a scarred eye is to have the lens fit centrally with enough movement for tear flow, but not too much that the lens is moving on every blink. There is a fine line between a loose fitting lens and a lens that fits too tightly, so putting in the effort to find the perfect lens for the patient initially will resolve a lot of future problems. In the writer’s experience, over eighty-percent of prosthetic lenses painted had been of standard design, not requiring a fitting set at all, so one shouldn’t see this as an intimidating task.
The Lab requires the following:
1. The best fit disposable lens; brand design, diameter, base curve and power.
2. Measuring the undamaged eye: iris and pupil diameter to be matched.
3. Photos of both eyes in the same photo, with the flash on, the flash off, indoors and outdoors.
If you want to try fitting a colour filter lens you will have to fit the patient with a trial lens from the fitting set with the colour already tinted, to test the efficiency of such lens. Most laboratories that manufacture these lenses will have fitting sets available with a variety of colours to choose from. Often, in these cases, the entire lens will be tinted to eliminate any peripheral light entering the eye. In less severe cases, patients will still benefit from a 5mm central tint.
Hand painted or tinted?
Hand painted lenses are only used for light coloured eyes, where a lot of iris detail is necessary to match the undamaged eye. It is very rare for a patient with a dark brown eye to need a hand painted lens, unless they require an exact brown colour match and have tried the tinted option with no success. Tinted lenses have no patterns and are tinted one colour, although some technicians have been able to incorporate a darker limbal ring to make the tinted iris look more natural. If cost is a factor for some patients who require a hand painted lens, they will rather opt for a basic tinted lens to cover the scarring on their eye.
Here are examples of a hand painted lens:
So whether it is an occluding lens or a pinhole lens, the two options above will apply. Hand painted for a light iris colour and tinted for a darker brown iris colour. Patients with brown eyes should be given the option of a hand painted lens, in case they are not satisfied with the tinted option. Hand painted lenses obviously involve more time and labour and are therefore more expensive.
Tinted lenses are translucent and light will be able to travel through the coloured portion of the lens. The standard brown tinted lens with black pupil tint is the most commonly ordered lens here in South Africa that is typically used to cover white scarring over the iris. These lenses are best suited for this as they don’t need to block out any light and are only covering a scar. When one needs to occlude vision or limit the light getting through the lens, the best option is an opaque backed lens. This opaque backing eliminates all light from entering through that portion of the lens.
Central scarring or cataracts can be masked with a black pupil tinted lens with a clear periphery, with the black pupil tinted 1mm-2mm larger than the current pupil/scarring. This black central tinted lens (tinted very dark) can also be used as an occluding lens if the patient doesn’t pick up the peripheral light/vision.
Patients with albinism can benefit from both of the above. A plain tinted iris lens with clear pupil (tinted pinhole with no opaque) or a plain tinted iris with clear pupil and opaque backing. The cheaper of the two options (being the tinted lens) with no opaque backing is most commonly ordered.
A pinhole prosthetic lens is likely to create a sensation of a restricted peripheral field, however, this can be adapted to over time. This is especially problematic for patients who had to deal with excessive glare due to an iris injury and it may be necessary to build up wearing time.
The hand painted lenses are often done with an opaque backing, this is mainly used so that the artist has an even surface on which to paint. It also helps the artist to paint the lens to the necessary colours and not have to worry about the influences from the scarring on the cornea and the environment. When painting a light coloured iris, you have to start on the lightest possible background to allow for the details to be added, adding to the reason why hand painted prosthetic lenses will be opaque.
These are the options available in custom prosthetic lenses:
- Black pupil tinted lens – this will cover any central scarring/ cataract and can even be used to occlude vision in some cases. (with a high plus front surface lens design)
- Painted/tinted lens to cover scarring – hand painted for light eyes or tinted for the darker brown eyes, no opaque backing is needed for the tinted lens as no light needs to be blocked in these cases.
- Occluding Lens – hand painted for light eyes or tinted for the darker brown eyes. A dark black full tint can be used in cases where patients cannot afford either the tinted brown or hand painted options.
- Pinhole lens – hand painted for light eyes or tinted for the darker eyes, both with opaque backing. A dark black iris tint can be used in cases where patients cannot afford either the tinted brown or hand painted options.
- Pinhole lens for Albanism – tinted brown with no opaque backing. (Also used in cases where patients cannot afford the tinted opaque lens)
The art of painting an iris
The intricacies of replicating an iris accurately are immense and a topic in its own right. Suffice to say, it requires a lot of patience, skill and understanding of all the peripheral factors that can influence the final outcome. One only has to consider all the colours present in a human iris, to appreciate how complex a process it must be to replicate an iris accurately.
The method of painting on the surface of the lens involves using an already cut and hydrated soft contact lens. A jig is used where opaque solution is added to create the white surface on the lens. This opaque white surface will block out the light allowing the artist to have an even and spherical background to paint on. The entire painting process has to be timed precisely, otherwise it can turn into a process that can take several days. The lens needs to be painted in its hydrated state so there is a short window for the paint to be added before the lens goes into a developing solution. The lens is then rehydrated again and the artist will add another layer of paint. This process is most difficult for the artist. He or she will have to know for certain that the colour which is applied to the lens in the first layer is not going to be affected by other colours that are applied in the next stage of the painting procedure.
Creating a master piece that will match the good eye very closely, demands good team work by the optometrist, the patient and the artist. It is important to begin with the end result in mind and all the factors that can influence the final outcome need to be recognised early on.
The process and intricacies of painting an iris on a hydrophilic lens deserves a space of its own. Vision will oblige in due course.