Here we described a case of post-AKC SEIs that resulted in decreased visual acuity due to the corneal surface irregularity. Although no significant corneal opacity was observed in the visual axis, irregularities in the corneal epithelial surface resulted in irregular astigmatism, leading to blurred vision. Even minor distortions in the corneal surface can reduce the quality of retinal images. Typically, in cases of SEIs after AKC, physicians focus only on the severity of opacity; however, irregularities of the corneal surface must also be noted. Unfortunately, a direct examination of the corneal surface using slit-lamp microscopy did not provide sufficient information to detect vision-reducing irregular astigmatism in the present case.

Recent advances in corneal imaging systems, such as SS-AS-OCT topography, have enabled a more precise understanding of the corneal surface [13]. However, it can be particularly challenging to keep children still for long periods. In fact, the color-coded map of SS-AS-OCT yielded complicated and unreliable results despite its applicability (Fig. 2A and B, panels i and j). In contrast, a Placido disc paired with an autorefractometer featuring a keratometer is widely accessible and can be rapidly performed, yielding results that are easy to interpret visually. The Placido rings are marked in black and white, enabling an easy display of irregularities. Although we used corneal topography (PR 8000) to detect the Placido ring patterns, similar observations could be obtained using a Placido disc paired with an autorefractometer featuring a keratometer. Thus, employing a simple topography with Placido ring mires facilitates the easy detection of abnormal corneal surfaces.

Pathologically, SEIs are immune responses to adenovirus antigens rather than viral multiplication [14]. Therefore, topical steroids are usually effective and offer a significant advantage in suppressing the subsequent progression to SEIs [15]. Nevertheless, SEIs flare up upon the tapering of steroids, resulting in persistent white opacities that can lead to vision loss [2, 5, 6]. In addition, the topical administration of corticosteroids can prolong viral shedding and infection [16, 17]. Alternatively, topical immunosuppressive agents, including cyclosporine A and tacrolimus, have been proposed as treatments for SEIs [2, 6, 9,10,11,12]. In our case, the irregularities of the corneal surface and distorted Placido ring mires on the corneal topography resolved after administration of 0.1% tacrolimus eye drops. We speculate that the 0.1% tacrolimus eye drops effectively suppressed the overactive immune response to residual dead viral particles, causing the irregular corneal surface. Similarly, recent studies have demonstrated a significant improvement in visual acuity in patients treated with topical tacrolimus [10, 11]. Despite potential adverse effects, including burning, tearing, irritation, photophobia, and redness [10], topical tacrolimus has the advantage of preventing intraocular pressure elevation, resulting in fewer SEI recurrences than topical steroid treatment [9, 12]. However, topical immunosuppressive agents also promote viral replication and prolong viral shedding [18]. Notably, combined povidone-iodine (polyvinylpyrrolidone-iodine; PVP-I) therapy with corticosteroids or immunosuppressant is proposed to accelerate clinical resolution and promote rapid eradication of adenovirus virions in patients with AKC [19, 20]. This warrants further prospective investigation.

In conclusion, this report highlights that vision loss due to SEIs after AKC may stem from an irregular ocular surface regardless of corneal opacity severity and the efficacy of topical tacrolimus in treating this condition. Moreover, it demonstrates the importance of observing Placido ring mires, a conventional and simple method that provides the most realistic projection of the corneal surface.