Features of keratoconic corneal anatomy observed with multiple imaging modalities and histology

Abstract

 

Purpose

 

This study compared the anatomic appearance of keratoconic corneas using three different imaging modalities and histology.

 

Methods

 

Prospective observational study. 12 keratoconic corneas, 4 corneas with stromal scar after infectious keratitis and 8 normal corneas from human donors were examined. Stromal scars were included as this condition can be misdiagnosed as keratoconus. Patients were imaged using spectral domain optical coherence tomography (OCT, Optovue) and in vivo laser scanning confocal microscopy (HRTII, Heidelberg) during pre-operative examinations preceding keratoplasty. Following transplantation, the removed corneal button was imaged ex vivo with full-field optical coherence microscopy (FFOCM, LLTech, France). The cornea was then fixed and sent for histology. Normal human donor corneas were imaged with FFOCM for comparison with the keratoconus and scar samples.

 

Results

 

FFOCM showed good low power view detail without artifacts from histological processing such as dissociation of collagen lamella and separation of the epithelium. Corneal structural changes related to keratoconus were noted for each patient and with each imaging modality according to the 5 stages proposed by by Sandali et al (Ophthalmology, 120:12 2013): (1: thinning of epithelial and stromal layers 2: hyperreflective anomalies at the Bowman’s layer (BL) and epithelial thickening 3: posterior displacement of the hyperreflective structures at BL, increased epithelial thickening and stromal thinning 4: pan-stromal scar 5: hydrops; 5a: acute onset - Descemet’s membrane (DM) rupture/dilaceration of collagen lamellae and large intrastromal cysts; 5b: healing stage - pan-stromal scarring with DM rupture). Additional criteria were added based on FFOCM views, for example, BL dehiscence and sub-epithelial fibrosis, observed in 4 stage 3 subjects, with BL displaced towards the stroma, indicating that the thinned stroma at stage 3 is compensated by thickened epithelium or sub-eptihelial fibrosis. Some aspects were more easily visible with FFOCM than histology, in particular fibrosis, Vogt’s striae and keratocyte organization. Scar samples showed fewer epithelial changes in comparison to keratoconus.

 

Conclusions

 

A classification of keratoconic corneas based on imaging with OCT, HRTII, FFOCM and histology is proposed, adding new criteria based on FFOCM views, which offer artifact-free images with good morphological detail.