GREG IS A 28-YEAR-OLD man who works as a policeman. He was diagnosed with keratoconus at the age of 22 and underwent epithelial-off cross-linking the following year. Although his condition has stabilized, he remains visually symptomatic.

He underwent topography-guided custom ablation treatment (T-CAT) laser surgery to try to reduce residual aberrations. Although he has 20/20 vision with glasses, he still has difficulty driving at night and working in dim light. He also feels that glasses are not optimal for his type of work.

The patient has been fit with corneal GP lenses in the past but has discontinued them due to discomfort. In addition, he has lost contact lenses on several occasions, leaving him vulnerable while on patrol. He tried to overcome these disadvantages with a piggyback system, but the handling of four lenses didn’t make sense to him. He wanted to explore other options.

While researching new technologies on the internet, he became interested in scleral lenses with aberration control. Dr. Google directed him to a clinic in the U.S., where he traveled for a consultation and fitting. Unfortunately, none of the four attempts have been successful so far. That’s why he’s now in my exam chair looking for other options.

Looking at the case, refraction, and topo maps, I was convinced to apply my colleague Dr. Daniel Brazeau’s rule of thumb: Any patient who can be corrected to 20/30 or better with glasses is considered a poor candidate for scleral fitting until proven otherwise.

The interplay of refractive indices between the different media and the lens, the fact that the lens is often decentered, and the prismatic shape of the fluid reservoir all contribute to creating optical aberrations that are difficult to compensate for (Hastings et al, 2019). Most importantly, they are the opposite of what the patient is used to. As a result, the image is compromised, upside down compared to what the patient is used to seeing. This is very disconcerting, to say the least. 

Trying to fix this represents a challenge. Forget about increasing the lens thickness or adding a front toric power. Higher front-surface asphericity may help, but it requires a lot of trial and error. And as the patient experienced, wavefront correction technology is still in development.

So, what can be done to improve this patient’s condition? Hybrid lenses can be a very interesting option, especially for nipple cones like was observed in this patient. I’ve used them many times in the past with great success. This becomes plan A.

Why not consider custom soft lenses? We prescribe these less frequently because they were associated with a mixed success rate in terms of vision (Jinabhai et al, 2014) or aberration correction (Penbe et al, 2023). Once made of hydrogel materials, the risks of hypoxic stress due to their low-oxygen-transmissibility are limited as they are now available in silicone hydrogel or made with thinner profiles (Chang and DeLoss, 2018).

However, lens instability (Chen et al, 2007) remains an issue and becomes problematic when a spherocylindrical power is prescribed. Nevertheless, there are still patients who can benefit from these lenses, with adequate comfort and vision (Gumus and Kahraman, 2016). So, that becomes plan B.

After a successful diagnostic trial, Greg decided to opt for my plan A. Hopefully, this will allow him to solve his vision problems to his satisfaction. For this reason, I keep plan B in my back pocket—just in case. CLS

References

1. Hastings GD, Applegate RA, Nguyen LC, Kauffman MJ, Hemmati RT, Marsack JD. Comparison of Wavefront-guided and Best Conventional Scleral Lenses after Habituation in Eyes with Corneal Ectasia. Optom Vis Sci. 2019 Apr;96:238-247.
2. Jinabhai A, O’Donnell C, Tromans C, Radhakrishnan H. Optical quality and visual performance with customised soft contact lenses for keratoconus. Ophthalmic Physiol Opt. 2014 Sep;34:528-539.
3. Penbe A, Kanar HS, Arsan AK, Kurna SA. Efficacy of custom-made soft keratoconus lenses on corneal aberrations and photic phenomena in patients with keratoconus: a corneal topography imaging based study. Int J Ophthalmol. 2023 Jan;16:67-74.
4. Chang C, DeLoss K. Contact Lenses After Corneal Transplantation. Contact Lens Spectrum. 2018 June;33:36-41,51.
5. Chen M, Sabesan R, Ahmad K, Yoon G. Correcting anterior corneal aberration and variability of lens movements in keratoconic eyes with back-surface customized soft contact lenses. Opt Lett. 2007 Nov 1;32:3203-3205.
6. Gumus K, Kahraman N. A New Fitting Approach for Providing Adequate Comfort and Visual Performance in Keratoconus: Soft HydroCone (Toris K) Lenses. Eye Contact Lens. 2016 Jul;42:225-230.