Not everyone with keratoconus can wear the customary type of contact lenses. These customary “hard” contact lenses – Rigid Gas Permeable (RGP) lenses – rest directly on the cornea, which is cone-shaped in keratoconus-afflicted people. For someone with cornea pain due to keratoconus, wearing RGP lenses can increase that cornea pain. Since “soft” contacts do not correct for astigmatism, eyesight in a person with keratoconus typically remains blurry with these lenses. Therefore, “soft” contacts are hardly ever considered appropriate corrective eyewear for a keratoconus-afflicted person. In contrast, scleral contact lenses do not rest on the cornea.
Described below are the differences between a “fitting” for RGP lenses and scleral lenses, and ways to decide which contact lens type is more appropriate for you.
Reasons Scleral Contact Lenses Require a More Skilled Fitting
Both “soft” and RGP contact lenses are small and correspond to the diameter of the person’s cornea. According to an article in the Journal of Optometry, the more de-centered the corneal cone, the more difficult and challenging the contact lens fitting. Basically, fitting contact lenses are more difficult in people with an abnormal cornea shape (such as occurs in keratoconus) than in people who have normal, dome-shaped corneas. Meanwhile, scleral contact lenses rest on the white of the eye (sclera) but need to additionally fit properly over the person’s cornea. Therefore, more skill is required to create well-fitting scleral contact lenses.
Benefits of Rigid Gas Permeable (RGP) Contact Lenses
Described below are five potential benefits of RGP contact lenses (per a PowerPoint presentation of the New England College of Optometry):
- Improved vision in people who have corneas with high toricity (i.e., corneas with high degree of apical curvature of the corneal meridians);
- Improved vision in people with corneas having irregular surfaces (such as occurs in keratoconus);
- Post-graft and post-surgical corneas (such as post-cornea implantation);
- Eye protection and improved vision in people who have aphakia (i.e., lack of eye’s own “natural” lens);
- Use in orthokeratology (temporary reshaping of cornea through RGP lens use to reduce refractive errors)
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Why Cost Should Not Be the Primary Deciding Factor in Choosing Contact Lenses
Scleral contact lenses for people with keratoconus are typically more expensive than traditional RGP contact lenses to correct vision. One reason is that scleral lenses require more measurements to produce the scleral lens to fit correctly in order to improve vision. Likewise, scleral contact lenses require more in-depth instructions for the person to learn how to insert and remove their scleral lenses.
Scleral contact lenses often also come with an applicator to enable the person to more easily insert and remove them without scratching them (rather than using fingers as more typical in inserting RGP lenses). However, people with corneal ulcers and/or cornea pain are usually unable to wear RGP contact lenses. Therefore – while RGP contact lenses may be less expensive to purchase – they are useless for correcting vision if the keratoconus-afflicted person does not wear them due to cornea pain!
Notably, the Cornea and Contact Lens Society of Australia recommends that people who have never-before worn RGP contact lenses be administered a drop of a local anesthetic during the fitting to reduce excessive reflex lacrimation (tearing of the eyes). The purpose of decreasing this “watering” of the eyes is so that the inserted RGP lens will remain in place, in order to both assess whether the “fit” is correct and vision correction has occurred.
How to Wear Scleral Contact Lenses
Unlike RGP contact lenses, scleral contact lenses include a reservoir for filling with sterile isotonic fluid that makes them more comfortable for keratoconus-afflicted people who have “dry eye” syndrome. Along with cornea pain, dry eyes are a possible keratoconus symptom that can preclude wearing RGP lenses for more than an hour at a time. Therefore, scleral contact lenses are often recommended to keratoconus-afflicted people with “dry eye” syndrome and/or corneal pain.
Parts of a Scleral Contact Lens
According to an article in Clinical Ophthalmology, scleral contact lenses consist of the following three parts:
- Scleral (haptic);
- Vault (responsible for corneal and limbal clearance of the lens);
- Optical (usually 0.2 mm larger than the horizontal visible iris diameter)
This article also notes that more attention during the fitting is typically given to the haptic part, the corneal (and limbal) clearance, and the edge of the lens than the other parts, as these especially affect the “on-eye” performance of the scleral lens itself.
If you have no other keratoconus symptoms besides myopia, astigmatism, and light sensitivity, RGP contact lenses may be quite suitable for you. It all depends upon whether the RGP lenses feel comfortable enough for you to wear them during your normal daily activities.
Consulting with the staff at the Precision Keratoconus Center can assist you in choosing between RGP contact lenses and scleral contact lenses, as well as other keratoconus treatment options.