Brian is one of the first scleral lens (SL) patients whom I fitted 10 years ago. For him, SLs have radically changed his life. At the time, the fitting philosophy was very different from what it is today. In Brian’s case, the manufacturer recommended an 18mm lens fitted with an initial reservoir thickness (RT) of 100 microns. There was obviously no question of toric peripheral curves (PCs). Because I had very little experience, I followed these instructions to the letter. On delivery, everything seemed fine. Vision and comfort being optimal, the patient was ecstatic.

I then lost the patient to follow up, because he moved to another state. He finally came back six years later, still wearing his original lenses! I expected to find the worst, knowing that by current standards, his SLs would be considered not optimally fitted. To my surprise, despite a light touch of the lens at the apex of the cone, the cornea remained free of staining and neovascularization.

With more experience under my belt, I immediately set out to refit the lenses using a contemporary approach (increased RT, toric PCs), a smaller diameter, and a higher-Dk material. Unfortunately, all of my attempts were in vain, particularly in terms of vision. Indeed, the patient’s visual acuity (VA) dropped by almost one line with the increased RT. It did not improve with time. In the end, I had to force myself to renew his lenses, identical to the original pair. Now, a year later, he still presents an intact cornea with no symptoms.

Points to Consider

I have some other patients who went through this same experience. We must therefore ask ourselves: Should we always vault significantly over the cornea, or, under certain circumstances, can we tolerate minimal RT, even a light touch?

Mechanical Stress Sclerals are large, heavy, thick lenses. Their weight is supported mostly by the conjunctiva but also by the reservoir. However, other large lenses—corneo-sclerals—are purposely designed to rest partly on the cornea (Michaud et al, 2019). To date, there is no clinical evidence that this type of fitting may be detrimental (Montalt et al, 2018).

If the weight of the lens is well distributed (toric PCs help) and there is no bearing on the cornea during all wearing hours, there should be no problems. On the other hand, if this touch results in a break of the ocular surface (fluorescein staining), then there will be a negative impact on comfort and a higher risk of scarring and infections.

If this mechanical stress occurs at the limbus, neovascularization will result (Barnett and Johns, 2017) due to the proximity of the blood vessels. A break in the cells’ tight junctions will generate epithelial bullae (Nixon et al, 2017). Contrary to popular belief (Korszen, 2019), limbal touch will not cause stem cell damage. These cells are located deep in the palisades of the limbus and cannot logically be disturbed by SL-induced mechanical stress (Hertsenberg and Funderburgh, 2015).

Physiological Stress However, some stem cells (not all) can be altered by hypoxic stress (Wang et al, 2016), which does not occur when the RT is minimal. There is also no physiological stress in the central cornea following RT reduction.

Visual Performance We know that the quality of vision provided by a small GP lens cannot be matched, especially in cases of keratoconus when lenses generate compression on the cone (such as the initial lens). Consequently, there is no harm, visually speaking, in keeping the SL close to the cornea without a true touch. A lower RT leads to better VA (Otchere et al, 2017).

Conclusion

I am not advocating the use of corneo-scleral lenses over true sclerals. But the point I want to demonstrate is that, with sclerals as with all other specialty lenses, the fitting process becomes the art of the possible. In some cases, limited or excessive RT over certain areas of the cornea can be clinically acceptable as long as a frank touch is avoided. Regular follow up is mandatory. As always, it is a matter of risk versus benefit. CLS

For references, please visit www.clspectrum.com/references and click on document #299.