If you have keratoconus and glasses no longer provide clear enough vision, you may be advised to try a specialised rigid contact lens.
Two common options are corneal RGP lenses and scleral lenses.
Both can provide excellent vision by creating a smoother optical surface over an irregular cornea, but they differ considerably in their size, comfort, stability and fitting characteristics.
So which one is better for keratoconus?
The answer depends on your individual eyes.
First, Aren’t Scleral Lenses Also RGP Lenses?
Technically, yes.
Scleral lenses and traditional corneal RGP lenses are both generally made from rigid gas-permeable materials.
However, when patients use the term “RGP”, they are usually referring to the smaller rigid lens that sits directly on the cornea.
A scleral lens is much larger. It is designed to vault over the cornea and rest on the white part of the eye, called the sclera.
For simplicity, we’ll refer to the smaller lenses as corneal RGP lenses throughout this article.
Why Are Specialised Contact Lenses Used for Keratoconus?
Keratoconus causes the cornea to become thinner and increasingly irregular in shape.
Glasses can correct short-sightedness and astigmatism, but as the cornea becomes more irregular, spectacles may no longer correct all of the optical distortion.
Rigid contact lenses can help because they create a new, regular optical surface in front of the cornea.
This can often provide much clearer vision than glasses alone.
What Is a Corneal RGP Lens?
A corneal RGP is a relatively small rigid lens that sits over the cornea.
The lens moves slightly with each blink and creates a smooth optical surface that helps compensate for the irregular corneal shape caused by keratoconus.
Advantages of corneal RGP lenses
For the right patient, corneal RGP lenses can provide:
- excellent visual clarity;
- good oxygen transmission;
- relatively simple handling and cleaning;
- a small lens diameter;
- good long-term performance; and
- often a less complex fitting process than a customised scleral lens.
Many patients with keratoconus wear corneal RGP lenses successfully for years.
Possible disadvantages
Some people experience:
- noticeable lens awareness;
- difficulty adapting to the lens;
- lens movement or decentration;
- fluctuating vision if the lens moves;
- discomfort in dusty or windy environments; or
- lenses occasionally becoming displaced.
As keratoconus becomes more irregular, it can also become more difficult to achieve a stable corneal RGP fit.
What Is a Scleral Lens?
A scleral lens is considerably larger than a traditional corneal RGP.
Rather than resting primarily on the cornea, it is designed to vault over the corneal surface and land further out on the sclera.
Before insertion, the bowl of the lens is filled with preservative-free saline.
This creates a fluid reservoir between the lens and the cornea.
Why Can a Larger Scleral Lens Be More Comfortable?
It seems counterintuitive, but a larger lens can sometimes feel more comfortable than a smaller one.
A corneal RGP interacts directly with the sensitive corneal surface and moves with blinking.
A scleral lens generally moves much less and rests on the less sensitive tissue over the sclera.
For some patients who have struggled with RGP comfort, this can make a substantial difference.
However, not everybody prefers scleral lenses, and comfort varies between patients.
Which Lens Is More Stable?
This is one of the main differences.
A corneal RGP needs to remain reasonably centred on an irregular corneal surface. In some patients with keratoconus, the lens may move or sit off-centre.
A scleral lens has a much larger landing area and usually moves very little once fitted.
This can make scleral lenses particularly useful when the corneal shape is:
- highly irregular;
- asymmetric;
- very steep; or
- difficult to fit successfully with a smaller lens.
Greater lens stability can also mean more consistent vision throughout the day.
Which Gives Better Vision?
Both can provide excellent vision.
A properly fitted corneal RGP may provide exceptionally sharp vision, and there is no reason to replace one that is working well simply because scleral lenses are available.
For other patients, a scleral lens may provide more consistent vision because it remains more stable on the eye.
It is important to understand that a scleral lens does not automatically produce perfect vision.
Keratoconus can cause complex optical distortions known as higher-order aberrations, and some of these may remain even with a well-fitted contact lens.
More customised optical designs may be considered in selected cases.
What About Comfort?
There is no universal winner.
Corneal RGP
Some people adapt very well and eventually notice the lenses very little.
Others remain conscious of the lens, particularly during blinking.
Scleral lens
The initial sensation may be unusual because the lens is large, but many patients find that a properly fitted scleral lens becomes quite comfortable once inserted.
The fact that it moves very little can be particularly helpful for people who struggled with smaller rigid lenses.
What About Insertion and Removal?
Corneal RGP lenses are small and relatively straightforward to handle once you have learned the technique.
Scleral lenses require a little more preparation.
The lens must usually be:
- held with an insertion device or fingers;
- completely filled with preservative-free saline;
- positioned without spilling the fluid; and
- inserted while the eyelids are held sufficiently open.
There is generally a learning period, but most patients can become confident with the technique after proper instruction.
Can Scleral Lenses Fog Up?
Some scleral lens wearers experience midday fogging, where vision becomes progressively hazy because material accumulates in the fluid reservoir beneath the lens.
This does not happen to everyone.
If it does occur, possible contributing factors may include:
- lens fit;
- tear-film debris;
- eyelid or ocular-surface inflammation;
- filling solution; or
- the amount of tear exchange beneath the lens.
Rather than simply accepting persistent fogging, the lens fit and ocular surface should be reassessed.
Are Scleral Lenses Better for Advanced Keratoconus?
They can be extremely useful, but not automatically.
A corneal RGP may still be an excellent option when it provides:
- good vision;
- reasonable comfort;
- stable centration;
- healthy corneal findings; and
- satisfactory wearing time.
Scleral lenses become particularly valuable when problems such as poor stability, discomfort or very irregular corneal shape make conventional lenses difficult to wear successfully.
What About After Corneal Cross-Linking?
Corneal cross-linking is intended primarily to reduce the risk of further keratoconus progression.
It does not necessarily make an irregular cornea regular again.
As a result, some patients still require specialised contact lenses after cross-linking to obtain their best vision.
Depending on the corneal shape and previous lens history, this could be a corneal RGP, scleral lens or another specialised design.
What About After a Corneal Transplant?
Even after a successful corneal transplant, significant astigmatism or corneal irregularity may remain.
Some patients therefore still require specialised contact lenses for their best vision.
Scleral lenses can be particularly useful in some post-graft eyes because they vault over much of the cornea, but these cases require careful assessment and individualised fitting.
So Which One Should I Choose?
You generally do not need to choose before your appointment.
The decision should be based on your examination findings.
A specialised keratoconus or contact-lens assessment may consider:
- corneal shape and severity of keratoconus;
- previous cross-linking or corneal surgery;
- corneal and ocular-surface health;
- previous contact-lens experience;
- lens comfort;
- stability;
- visual requirements;
- work and lifestyle; and
- how easy the lens will be for you to handle.
For some patients, a corneal RGP remains the simplest and most effective option.
For others, a scleral lens provides better comfort, stability or visual consistency.
And occasionally, another design such as a custom soft or hybrid contact lens may be more appropriate.
Keratoconus and Scleral Lens Assessment in Sydney
At Westmead Eyes, we assess patients with keratoconus and irregular corneas to determine which contact-lens design is most appropriate for their individual eyes.
The goal is not simply to fit the largest or most advanced lens available. It is to find the lens that provides the best combination of vision, comfort, stability and long-term eye health.
Learn more about Keratoconus & Scleral Lenses Here
If you already wear RGP lenses but are experiencing discomfort, lens movement or inconsistent vision, a specialised contact-lens assessment can help determine whether your current design remains suitable.