ANATOMICAL PATHOLOGY Histopathological study of 49 cases of keratoconus BRUNO F. FERNANDES*, PATRICK LOGAN*, MOYSES E. ZAJDENWEBER*, LEONARDO N. SANTOS*, DEVINDER P. CHEEMA{ AND MIGUEL N. BURNIER,JR*{ *Department of Ophthalmology and Pathology, The McGill University Health Center and Henry C. Witelson Ocular Pathology Laboratory, Montreal, {Department of Ophthalmology, The McGill University Health Center, Montreal, Canada; {Department of Ophthalmology, Federal University of Sa˜o Paulo, UNIFESP/EPM, Sa˜o Paulo, Brazil Summary Aims: Keratoconus is a bilateral and asymmetrical corneal ectasia. The pathophysiology of this disorder has yet to be fully elucidated. The purpose of our study was to document the prevalence of the most common morphological features of keratoconic corneas. Methods: A retrospective analysis of 49 cases diagnosed as keratoconus between 2001 and 2006 was undertaken. Histopathological reports were reviewed to obtain data such as age and gender. Specimens were fixed in 10% buffered paraformaldehyde solution for 24 h, bisected through the centre of the button, and embedded in paraffin. Sections were stained with haematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) for light microscopic examination. Results: The studied group was composed of 29 men and 20 women. Age at the time of the penetrating keratoplasty was 39 + 14 years (mean + standard deviation). Forty of the 49 specimens (82%) presented with epithelial thinning. Other common features of keratoconus included breaks in Bow- man’s layer in 35 (71%), compaction of the stromal collagen fibres in 31 (63%), and folds in Descemet’s membrane in 31 (63%) cases. Other less common histopathological findings were: presence of superficial iron deposits in 14 (29%), deep stromal scarring in 12 (24%), epithelial scarring in 11 (22%), endothelial cell loss in 11 (22%), and breaks in Descemet’s membrane in nine (18%) cases. Conclusions: Some of the histopathological findings asso- ciated with keratoconus are subtle. It is important to be aware of them in order to properly confirm the clinical diagnosis. Key words: Keratoconus, pathology, cornea, ectasia, transplant. Received 17 July, revised 26 September, accepted 3 October 2007 INTRODUCTION Keratoconus is a progressive, non-inflammatory, bilateral and asymmetrical corneal ectasia. 1 It was originally de- scribed in 1854 as a series of cases with conical corneas in patients whose vision could not be improved using corrective lenses. 2 This non-inflammatory disorder causes the affected cornea to bulge, resulting in a cone-shaped appearance, progressive myopia and irregular astigmatism. Even though in its earlier stages keratoconus presents symptoms similar to conventional refractive errors, the disease has the ability to progress into an affliction that can markedly affect vision. 3 The incidence and prevalence of keratoconus is approximately 1 per 2000 and 54.5 per 100 000 in the general population, respectively. 4 Keratoconus is diagnosed clinically using slit-lamp examination, corneal topography, or pachymetry. 4 Rabino- witz reviewed the clinical signs of keratoconus in 1998. 4 The seven key signs of keratoconus, proposed by Duke-Elder in 1965 5 remained practically unchanged: stromal thinning (usually central or paracentral); an endothelial reflex at peak of the cone; Vogt’s striae (vertical lines deep within the corneal stroma); an increased visibility of the corneal nerve fibres; Fleischer’s ring (the deposition of iron at the base of the cone); ruptures of Descemet’s membrane; and ruptures in Bowman’s layer in advanced cases producing superficial linear scars. Typically, mild keratoconus is treated with rigid contact lenses. 4 A patient with keratoconus has a 10–20% lifetime chance of undergoing penetrating keratoplasty (PKP), which consists of the removal of the diseased cornea and corneal transplantation. 4 Indication of corneal transplantation is reserved for those with central corneal scarring or those that cannot be fitted with contact lenses. 6 Nevertheless, kerato- conus is still one of the leading indications for PKP. 7,8 The pathophysiology of this disorder has yet to be fully elucidated. There has been some evidence to suggest that increases in the levels of specific proteases results in epithelial degradation and may play a role in the thinning of the cornea. 9–11 The purpose of our study was to investigate the prevalence of the most common morphological features of keratoconic corneas in order to provide insight into the progression of this disease. MATERIALS AND METHODS Patients A retrospective analysis was undertaken of 49 cases diagnosed as keratoconus between 2001 and 2006 from The Henry C. Witelson Oph- thalmic Pathology Laboratory and Registry, Montreal, Canada. Histo- pathological reports were reviewed to obtain data such as age and gender. Tissue samples Specimens were previously fixed in 10% buffered paraformaldehyde solution for 24 h. Corneal buttons were placed on a flat surface with the Pathology (October 2008) 40(6), pp. 623–626 Print ISSN 0031-3025/Online ISSN 1465-3931 # 2008 Royal College of Pathologists of Australasia DOI: 10.1080/00313020802320648