Bowman's layer encystment in cases of persistent Acanthamoeba keratitis

Hideaki Yokogawa, Akira Kobayashi, Natsuko Yamazaki, Yasuhisa Ishibashi, Yosaburo Oikawa, Masaharu Tokoro, Kazuhisa Sugiyama, Hideaki Yokogawa, Akira Kobayashi, Natsuko Yamazaki, Yasuhisa Ishibashi, Yosaburo Oikawa, Masaharu Tokoro, Kazuhisa Sugiyama

Abstract

Background: The purpose of this study was to report Acanthamoeba encystment in Bowman's layer in Japanese cases of persistent Acanthamoeba keratitis (AK).

Methods: Laser confocal microscopic images of the cornea were obtained in vivo from 18 consecutive eyes from 17 confirmed AK patients. Retrospectively, 14 cases treated over 4 months were categorized as a nonpersistent group and three cases that required prolonged therapy for more than 6 months were categorized as a persistent group. Clinical outcomes based on final best-corrected visual acuity were retrospectively analyzed, and selected confocal images were evaluated qualitatively for abnormal findings.

Results: The final best-corrected visual acuity was significantly lower (P < 0.01) for patients in the persistent group compared with that in the nonpersistent group. At the initial visit, in vivo confocal microscopy demonstrated Acanthamoeba cysts exclusively in the epithelial layer in both the nonpersistent group (80%) and the persistent group (100%). At a subsequent follow-up visit, numerous Acanthamoeba cysts were observed in the epithelial cell layer and in Bowman's layer in all patients with persistent AK, but Acanthamoeba cysts were undetectable in all cases with nonpersistent AK tested.

Conclusion: Invasion of cysts into Bowman's layer was characteristically observed in patients with persistence of AK. This finding suggests that invasion of Acanthamoeba cysts into Bowman's layer may be a useful predictor for a persistent clinical course.

Keywords: Acanthamoeba keratitis; Bowman’s layer; encystment.

Figures

Figure 1
Figure 1
Slit lamp and in vivo laser confocal microscopic examination of case 15. (A) The right cornea on initial presentation to our hospital. Epithelial defects and subepithelial opacities were observed in the central cornea by slit-lamp biomicroscopy. Radial keratoneuritis lesions (arrows) and inflamed conjunctiva were also observed. (B) Recurrence of AK one month after treatment. Subepithelial opacity and anterior chamber reaction were increased. (C) In vivo laser confocal microscopy of recurrent AK showed a number of highly reflective, high-contrast round-shaped particles 10–15 μm in diameter (arrows), suggestive of Acanthamoeba cysts in the epithelial basal cell layer (bar 50 μm). Double-walled cysts were not detectable. (D) In the epithelial basal cell layer, numerous dendritic cells (putative Langerhans cells) were observed. A decrease in subbasal nerves (arrows) was also noted. (E and F) At the Bowman’s layer level, numerous Acanthamoeba cysts were observed as highly reflective, high-contrast particles with an approximate diameter of 10 μm. Some of the Acanthamoeba cysts were present in small clusters (arrows). Note the diameter of the cysts in Bowman’s layer (10 μm) was smaller than that observed in the epithelial cell layer (10–15 μm). (G) Activated keratocytes forming a honeycomb pattern were observed in the stromal layer. However, Acanthamoeba cysts were not detectable in the deep stroma in this case. (H) Clusters of leukocytes (arrows) were observed in the endothelial layer. (I) Slit-lamp photograph 9 months after treatment. Notes: The AK healed after 13 epithelial debridements with topical micafungin 0.1% and topical chlorhexidine 0.05%. Despite slight stromal scar formation, the best corrected visual acuity recovered to 20/32 OD. Abbreviations: AK, Acanthamoeba keratitis; OD, oculus dexter (right eye).
Figure 2
Figure 2
Slit-lamp and in vivo laser confocal microscopic examination of case 16. (A) The left cornea at initial presentation to our hospital. Subepithelial opacities and radial keratoneuritis lesions (arrows) were observed by slit-lamp biomicroscopy. Inflamed conjunctiva was also observed. (B) AK recurred 50 days after treatment. Ring-form infiltration appeared. Anterior chamber reaction increased. (C) In vivo laser confocal microscopy of recurrent AK showed a number of highly reflective, high-contrast particles 10–15 μm in diameter, suggesting Acanthamoeba cysts in the epithelial basal cell layer (bar 50 μm). (D) Oblique view of the superficial cornea. Acanthamoeba cysts (arrows) were clearly recognized in Bowman’s layer. (E and F) In Bowman’s layer, characteristic clusters of Acanthamoeba cysts were observed as highly reflective, high-contrast particles with a diameter of approximately 10 μm. (G) The superficial stroma showed high reflectivity without Acanthamoeba cysts. (H) In the endothelial layer, leukocytes were observed. (I) Slit-lamp photograph 12 months after treatment. Notes: The AK healed after 20 epithelial debridements with topical micafungin 0.1% and topical chlorhexidine 0.05%. Despite stromal scar formation, the best corrected visual acuity had recovered to 20/60 OS. Abbreviations: AK, Acanthamoeba keratitis; OS, oculus sinister (left eye).

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