With amblyopia patients, every case is unique and the treatment always presents many challenges. The primary management depends on the type and depth of the amblyopia, and the secondary management is based on the compliance to treatment from the child and parent. But in both of these elements, contact lenses can play an integral role in the management of this condition.
Amblyopia develops when there is decreased visual stimulation during the critical period of visual development. Common causes are anisometropia, strabismus and vision deprivation (most commonly from congenital cataracts and ptosis). Treatment of amblyopia includes correcting the refractive error and occlusion or penalization of the non-amblyopic eye. At times, surgical intervention is necessary to correct muscle imbalance, remove cataracts or correct a ptosis.
But, as we all know, it is never that simple. For many different reasons, young children will often not tolerate traditional amblyopia treatment. They will not like glasses on their face, nor will tolerate occlusion by patching. There are many cases where the glasses initially blur their vision during the adaptation period, which can lead to kids looking over their glasses. Children, especially young children, often don’t understand the treatment, and why it is necessary.
This is where contact lenses can come into play. There are times when contact lenses are a good option to improve compliance, help adaptation and improve cosmesis, but in some cases, contact lenses are the standard of care in amblyopia treatment. We will discuss three important areas when it comes to using contact lenses to help treat amblyopia: anisometropic amblyopia, unilateral aphakia from congenital cataracts and occlusion therapy.
Anisometropia is one of the most common causes of amblyopia. It presents as anisohyperopia, anisomyopia or anisoastigmatism—each one unique in their management. The standard of care is to correct the refractive error with spectacles, then implement occlusion patching when the anisometropia is more significant or if correction alone is not improving the amblyopia.
Spectacle correction is typically the starting point for this condition, but if the difference of the required correction between the eyes is significant (>5.00D) contact lenses become the preferred choice. Unlike spectacle correction, contact lenses will reduce anisokonia, minimize prismatic effects during eye movements, increase peripheral field of view and decrease peripheral distortions. Improving the visual effects caused by spectacles can help with important things, such as adaptation and cosmesis. But, to a greater extent, these visual distortions can lead to diplopia or suppression, which is counter to the treatment we are trying to provide. In these instances, contact lenses provide the anisometropic patient with the best opportunity for binocular vision development and amblyopia reversal.
In most anisometropia patients, standard soft disposable contact lenses can be used. You should use silicone hydrogel materials to fit toddlers whenever possible—their lifestyle includes frequent naps, so high Dk materials are important. If a patient has very high astigmatism, very high sphere or requires atypical fitting parameters (e.g., steep base curves, small diameters), custom designs should be considered. Most custom designs come in monthly, quarterly and yearly replacement. A few recommended manufacturers are Alternative Vision Solutions, Specialeyes, Gelflex or CooperVision Hydrasoft.
The diagnosis, treatment and management of congenital cataracts come at a very early age. Visual prognosis is based on age, density of the cataract, whether there is an accompanying disease like persistent hyperplastic primary vitreous (PHPV) and whether it is unilateral or bilateral. For a good visual outcome, it is essential to intervene surgically, give the proper optical correction and implement aggressive amblyopia therapy before the infant is six months old. In these patients, compliance is critical.
Contact lens wear is the standard of care for optical correction. Spectacles are only used if the lenses are lost or damaged and in instances of poor compliance. In general, infants do not tolerate glasses well. So, in addition to the asymmetric weight of a unilateral aphakic spectacle correction and the large image size disparity between the eyes, this makes contact lenses essential for unilateral aphakic correction. A typical pediatric aphakic spectacle power increases the image size up to 30%, while a contact lens increases the size by up to 12%. Intraocular lenses provide the best optical correction, but are not used in most cases until one and a half to two years of age.
Bausch + Lomb’s Silsoft Super Plus remains the lens of choice for correcting infants who had cataract surgery and had not received an intraocular lens implant. Silsoft is made of the silicone elastomer material elastofilcon. This material continues to have the highest oxygen permeability (Dk: 340) of any material available. It is available in parameters necessary to fit an infant cornea:
• Base curves: 7.5mm, 7.7mm and 7.9mm
• Diameter: 11.3mm
• Powers: +23.00D to +32.00D (in 3.00D steps)
Extended parameters are available for older children.
The high level of oxygen permeability makes this material safe for extended wear, which is necessary for these patients. As a group, the pediatric population doesn’t often have issues with protein or lipid build-up on lenses, but silicone elastomer material is prone to these issues. The recommended disinfection and cleaning methods for Silsoft is a hydrogen peroxide-based care system, such as Clear Care (CIBA Vision).
Unilateral Aphakic Fitting
It is important not to delay the lens fitting of an aphakic infant. Typically, around one week post surgery or sooner, the eye has healed and is ready to be fit. It is recommended to start by putting on a fitting lens of the steepest base curve (7.5mm) and a higher power (+29.00D). To determine the power, do over-retinoscopy with loose lenses with the fitting lens in place. Then, because an infant’s visual world is within three feet of them, it is important to add +3.00D to the power that you measure. Next, observe the lens to be sure it remains centered and that it is not moving off the cornea under the lid. If so, it may be too flat.
Other fitting issues could be air bubbles under the lens. This can mean that the lens is too steep. I recommend letting the family go home with the fitting lens while you wait for the new lens to be shipped. Ideally, the lens will stay in for the entire week, so that the infant is getting a nearly corrected image during this critical time.
When the new lens comes in, switch out the fitting lens for the new one. Once the new lens is inserted, re-check the over-retinoscopy and observe the fit for good centration and absence of bubbles under the lens. During this dispensing visit, teach the parents insertion, removal, cleaning and care. At this time, you should also start patching; depending on the severity of the amblyopia, two to six hours of patching per day every day is recommended. Make sure the parents know to call if there are problems with insertion, removal or if the lens is lost.
Your first follow-up visit should be at two weeks. At this visit, you will again check the over-retinoscopy, the lens centration and the eye health response. It is helpful to have a hand-held slit lamp for these evaluations. If you don’t, use a direct ophthalmoscope or a transilluminator. Infant lens power will change rapidly, and when it does, it’s important to change the lens. During follow-up exams, monitor their amblyopia with visual fixation, following and induced tropia preference, and check for strabismus development. Continued follow-up care takes place every month for the first year and every three months after the first year.
The prognosis of the visual outcome often depends on the proper education and compliance of the parents. They need to understand the benefits and risks of the treatment and that their participation will directly influence their child’s long-term vision. You must teach parents the skills they will need, educate them of the difficulties they will encounter and offer encouragement that the process will get easier and that their child will adapt.
An important part of most amblyopia therapies is to implement an occlusion regimen by patching the non-amblyopic eye. To achieve this, we recommend the soft patches that slide over spectacles because they are comfortable and give complete coverage so the patient can’t peek around it. If the patient doesn’t require glasses or is very young, adhesive patches will do the job. Compliance frequently becomes a problem because the child pulls off the patch, creates peek holes, develops a secondary dermatitis from the adhesive patch or just plain won’t wear the patch. When this happens, you can turn to atropine penalization, over plussing the non-amblyopic eye or applying a Bangerter foil for penalization. Each of these options has potential side effects or downsides. Kids may take issue with constant blur, the use of drops, or they might find it easy to look around or take off the foils.
Occlusive contact lenses, which block vision in the non-amblyopic eye, are an effective option for the treatment of amblyopia. Nearly 30% of the subjects in one study successfully wore an occluder contact lens after failure of traditional occlusion therapy.1 The study followed infants and young children with dense amblyopia from unilateral aphakia, strabismic amblyopia and mixed mechanism amblyopia. Generally, it is advised that occluder lenses are worn for less than 10 hours per day. This reduces the chance of occlusion amblyopia of the non-amblyopic eye and the opportunity for corneal complications. When using occluder contact lenses, we must monitor the corneal health related to contact lens wear because we are fitting the normal eye of an amblyopic patient. Occluder contact lenses can be more effective in children who are already using contact lenses. Otherwise, it requires additional motivation from the parents to help with the handling and care.
The parameters of an occluder lens are determined by fitting a clear lens of the same design as the opaque lens. There are options for the final design of an occluder lens: a purely black center or a cosmetic opaque contact lens. The opaque zone should be made at least 12mm, so that the patient has a harder time seeing around it. Some children become good at moving the lens to the side or blinking to see around the lens, which makes the treatment less effective. Cosmetic opaque contact lenses have a full iris and blacked-out pupil. They look more natural and are a better option if the child will be wearing it at school or in public.
Many companies make occluder lenses and opaque cosmetic lenses. You can get them from the big manufacturers, such as CIBA Vision and CooperVision or smaller companies, such as Adventures in Color and Specialty Tint Lab. The vast majority are daily-wear yearly replacement lenses.
Up for the Challenge?
Treating and managing amblyopia can present many challenges, but practitioners have a number of treatment options to choose from. Contact lenses can be a valuable tool to help treat these patients and, coupled with protective eyewear, are a great option. Contact lenses provide vision that allows for better adaptation, improved cosmesis and comfort. In extreme cases, contact lenses are necessary to avoid diplopia and suppression, which is mandatory to treat amblyopia. Considering the patient population, the fitting and instruction of contact lenses requires extra patience, but if you are up for the challenge, the results are very rewarding.
Dr. Strako is the director of Pediatrics at North Suburban Vision Consultants in Deerfield, Ill., and staff doctor in the Division of Pediatrics at the Wheaton Eye Clinic.
1. Joslin CE, McMahon TT, Kaufman LM. Effectiveness of occluder contact lenses in improving occlusion compliance in patients that have failed traditional occlusion therapy. Optom Vis Sci. 2002 Jun;79(6):376-80.