The case described in this paper demonstrates how corneal irregular astigmatism can be caused by epithelial hyperplasia and how it can be managed by epithelium removal only. It also highlights the importance of epithelial mapping for diagnosis and management decision-making in this and similar cases.

Epithelial mapping revealed a nasal focal area of epithelial hyperplasia (68 μm) in the left eye that coincided with the area of steepest curvature. Reinstein et al. reported that in normal corneas, epithelium mean central thickness was 53,4 μm, with the superior epithelium being 5,7 μm thinner than the inferior epithelium and 1,2 μm thicker in the nasal than in the temporal regions [5]. Thus, the epithelial pattern in our case obviously did not correspond to that of a normal cornea.

The nasal location of the corneal steepening, together with the normal pachymetry map, normal posterior elevation and tomographic indices, as well as the corneal thickness spatial profile and the percentage of thickness increase curves, and the negative result of the keratoconus algorithm ruled out keratoconus. The fact that epithelial hyperplasia coincided with nasal steepening contradicted a diagnosis of keratoconus, in which epithelial thinning over the cone would be expected. Contact lens-induced corneal warping usually shows epithelial hyperplasia over the steep area of corneal curvature [9]. However, our patient had not used contact lenses for five days before surgery, and preoperative topography was normal. In fact, she had not worn contact lenses since the ICL implantation, meaning she had gone 20 months without contact lenses when she noticed the decrease in visual acuity in her left eye.

Focal epithelial hyperplasia with accompanying corneal steepening mimicking keratoconus can be caused by different conditions: inflammatory conditions (blepharitis, Meibomian gland dysfunction, viral keratitis), neoplasic conditions (preclinical corneal intraepithelial neoplasia), degenerative conditions (Salzmann nodular degeneration, peripheral hypertrophic subepithelial corneal degeneration, epithelial basement membrane dystrophy), or traumatic conditions [2, 4, 6,7,8,9]. All these conditions were ruled out after a careful slit lamp examination coupled with AS-OCT exams. Recently, Levy et al [10] showed that epithelial map pattern recognition combined with a quantitative analysis of epithelial thickness, is relevant for the diagnosis of ocular surface diseases and for distinguishing various diseases from each other. They described 14 epithelial map patterns, some of which were related to the diagnosis of certain ocular surface pathologies. However, none of these patterns fit with the pattern observed in our patient for whom endothelial cell density and ICL vault were within normal limits in both eyes and no endothelial alteration or corneal edema was detected. In addition, the evolution of the case was observed over the course of six months, which would have allowed any possible pathology to manifest itself.

The patient developed this irregular astigmatism after ICL implantation. One may speculate as to whether the irregular corneal astigmatism may have been induced by the corneal incision. The nasal area location of corneal steepening does not support the hypothesis of a surgically-induced alteration, nor does the presentation 20 months after ICL implantation. Had the surgical incision played a role in the nasal steepening, it would have become manifest soon after surgery. An alteration of epithelial mapping has been reported after cataract surgery with a slight increase in central epithelial thickness [11]. In this case, there was a paracentral hot spot on the epithelial map, not a central one. No report dealing with epithelial mapping alteration after ICL has been published.

We also speculated as to whether the focal hyperplasia was due to eye rubbing. The patient reported rubbing her eyes though very rarely. There are few publications regarding the effects of eye rubbing on the corneal epithelium [12,13,14]. No significant differences in epithelial thickness were found after eye rubbing in one paper [12], while epithelial thinning changes were described in two other studies [13, 14]. None of these epithelial thinning map patterns are consistent with the localized epithelial thickening we observed in our patient and, in addition, the hot spot of epithelial hyperplasia persisted without changes after six months without eye rubbing.

Due to the epithelial origin of the irregular astigmatism, we decided to proceed with solely epithelial removal first. We performed intraoperative topography with the aim of confirming the epithelial origin of the irregular astigmatism. Topography immediately after removing the epithelium showed a perfect bow tie pattern, further supporting the epithelial origin of the hot spot observed in topography.

A recently-published paper illustrated a similar scenario, though in that case, the patient had a history of contact lens intolerance and the cause of the irregularity was related to corneal warpage according to some, but not all of the panelists [6]. There were no other corneal alterations that could have been the cause of the irregularity and corneal ectasia had been excluded since the pachymetry map was normal, different keratoconus algorithms ruled out keratoconus and, in addition, as in our case, and unlike in keratoconus, the area of epithelial hyperplasia coincided with the area of corneal steepening. Unlike our case, this paper did not provide intraoperative topography but the management of the case was the same, with epithelial removal only, which successfully reverted the condition. It is our opinion, and that of other authors, that epithelial removal only can be used to treat epithelial hyperplasia in the absence of underlying stromal irregularity [1, 6]. Although some of the panelists in the previous paper [6] suggested and agreed with this approach, and Hwang [1] proposed the same procedure for the treatment of epithelial hyperplasia in the absence of any underlying stromal irregularity, we are not aware of any published series of cases evaluating the results of this procedure to treat similar cases. Our case does provide further supports for this approach.

The main limitation of this report is that the information provided here was obtained from an isolated case. In addition, a longer follow-up would be required to evaluate whether the epithelial alteration could relapse.

In conclusion, focal epithelial hyperplasia may induce irregular astigmatism. Epithelial mapping is a very useful technology to assess cases with irregular topography. De-epithelization as an isolated procedure may be useful for the successful management of these cases. Further research is required to fully understand the mechanism that triggers the development of a focal area of epithelial hyperplasia in an otherwise normal eye.