The case described in this paper shows how corneal irregular astigmatism can be caused by epithelial hyperplasia and how it can be managed by epithelium removal only. It highlights the importance of epithelial mapping in the diagnosis and management decision in this and similar cases.
Epithelial mapping revealed a nasal focal area of epithelial hyperplasia (68 µm) in the left eye that was coincident 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 and 1,2 µm thicker nasal than temporal.5 Thus, the epithelial pattern in our case obviously did not correspond with that of the 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 percentage thickness increase curves, and the negative result of the keratoconus algorithm ruled out keratoconus (made the diagnosis of keratoconus very unlikely). The epithelial hyperplasia that coincided with nasal steepening was not in agreement with the keratoconus diagnosis, 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 (blepharitis, Meibomian gland dysfunction, viral keratitis), neoplasic (preclinical corneal intraepithelial neoplasia), degenerative (Salzmann nodular degeneration, peripheral hypertrophic subepithelial corneal degeneration, epithelial basement membrane dystrophy), or traumatic.2, 4, 6– 9 All these conditions were ruled out after careful slit lamp examination coupled with AS-OCT exams. Recently, Levy et al10 showed that epithelial map pattern recognition combined with 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 of our patient. Endothelial cell density and ICL vault were within normal limits in both eyes and no endothelial alteration of the corneal edema was detected. In addition, the evolution of the case was observed for six months, which would have allowed any possible pathology to manifest itself.
The patient developed this irregular astigmatism after ICL implantation. One may wonder whether the irregular corneal astigmatism could 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. Should the surgical incision have played a role in the nasal steepening, it would have become manifest early after surgery. However, no alteration was found in the other eye–which had also undergone the same surgery–and there is no report dealing with any epithelial mapping alteration after ICL implantation. An alteration of epithelial mapping has been reported after cataract surgery with slight increase in the central epithelial thickness.11 In this case, there was a paracentral hot spot in the epithelial map, not a central one.
We wondered whether the focal hyperplasia could be due to eye rubbing. The patient acknowledged rubbing her eyes although very rarely. There are few publications about the effects of eye rubbing on the corneal epithelium. McMonnies et al found that central epithelial thinned immediately after eye rubbing, whereas it came back to baseline thickness after 30 minutes.12 The mid peripheral epithelial thickness behaved in the same way, but it recovered the baseline thickness 45 minutes after rubbing. However, in another study using spectral domain optical coherence tomography to measure epithelium thickness, no significant differences were found between before and after eye rubbing measurements.13 Recently, Loureiro et al found an inferotemporal epithelium thinning in eyes of young atopic patients who rubbed their eyes, comparing them with a control group. Corneal epithelial thickness was measured by anterior segment optical coherence tomography. Furthermore, they found more epithelial thinning in the eye which corresponded on the side of the dominant hand.14 None of these epithelial thickness map patterns are consistent with the one we found in our patient. 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. The 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, although 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 be the cause of the irregularity and corneal ectasia had been excluded since pachymetry map was normal, different keratoconus algorithms ruled out keratoconus and in addition, as in our case, and contrary to keratoconus, the area of epithelial hyperplasia coincided with the area of corneal steepening. Differently to 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 could be used to treat epithelial irregularity in the absence of underlying stromal irregularity.1, 6 In the paper mentioned above6, although some of the panelists suggested and agreed with this approach, and Hwang1 proposed the same procedure for the treatment of epithelial irregularity in absence of underlying stromal irregularity, we are not aware of any published series of cases evaluating the results of this procedure to treat similar cases, and Hwang did not cite any paper to support his statement1. Thus, we think that our case further supports this approach and may be of interest. In addition, we showed the series of topographies displaying the progressive development of this irregular astigmatism due to epithelial hyperplasia of unknown origin. The intraoperative topography of Bowman’s layer was obtained, confirming that the cause of the irregularity was the epithelial hyperplasia.
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 to manage these cases successfully. Further investigations are required to fully understand the mechanism that may trigger the development of a focal area of epithelial hyperplasia in an otherwise normal eye.