Fourier-domain optical coherence tomography imaging in keratoconus: a corneal structural classification.
OBJECTIVE
To study corneal morphologic changes in a large keratoconic population and to establish a structural optical coherence tomography (OCT) classification.


METHODS
Cross-sectional, observational study.


METHODS
A total of 218 keratoconic eyes from 218 patients and 34 eyes from 34 normal subjects.


METHODS
A Fourier-domain OCT system with 5-μm axial resolution was used. For each patient, 3 high-resolution scans were made across the keratoconus cone. All scans were analyzed by keratoconus specialists who were not given access to patients' clinical and topographic data, and who established an OCT classification. The reproducibility of the classification and its correlation with clinical and paraclinical characteristics of patients with keratoconus were evaluated. The OCT examinations were performed every 4 months to follow up structural corneal changes.


METHODS
Evaluation of the structural corneal changes occurring in keratoconus cases with various stages of severity based on OCT findings.


RESULTS
Fourier-domain OCT classification containing 5 distinct keratoconus stages is proposed. Stage 1 demonstrates thinning of apparently normal epithelial and stromal layers at the conus. Stage 2 demonstrates hyperreflective anomalies occurring at the Bowman's layer level with epithelial thickening at the conus. Stage 3 demonstrates posterior displacement of the hyperreflective structures occurring at the Bowman's layer level with increased epithelial thickening and stromal thinning. Stage 4 demonstrates pan-stromal scar. Stage 5 demonstrates hydrops; 5a, acute onset: Descemet's membrane rupture and dilaceration of collagen lamellae with large fluid-filled intrastromal cysts; 5b, healing stage: pan-stromal scarring with a remaining aspect of Descemet's membrane rupture. The reproducibility of the classification was very high between the corneal specialist observers. Clinical and paraclinical characteristics of keratoconus, including visual acuity, corneal epithelium and stromal thickness changes, corneal topography, biomechanical corneal characteristics, and microstructural changes observed on confocal microscopy, were concordant with our OCT grading.


CONCLUSIONS
Optical coherence tomography provides an accurate assessment of structural changes occurring in keratoconus eyes. These changes were correlated with clinical and paraclinical characteristics of patients. The established classification not only allows structural follow-up of patients with keratoconus but also provides insight into the pathogenesis of keratoconus and treatment strategies for future research.
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France. Electronic address: sanotman1@yahoo.fr.
Otman
O
Sandali
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France; National Institute of Health and Medical Research, Cordeliers Research Center, Team 17: Physiopathology of Ocular Diseases: Therapeutic Innovations, Pierre and Marie Curie University - Paris 6, Paris, France.
Mohamed
M
El Sanharawi
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France.
Cyril
C
Temstet
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France.
Taous
T
Hamiche
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France.
Alice
A
Galan
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France.
Wajdene
W
Ghouali
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France.
Isabelle
I
Goemaere
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France.
Elena
E
Basli
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France.
Vincent
V
Borderie
Centre Hospitalier National d'Ophtalmologie des XV-XX, Pierre & Marie Curie University Paris 06, Research Team 968, Institut de la Vision, Paris, France.
Laurent
L
Laroche
D000293:Adolescent; D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D003315:Cornea / Q000473:pathology*; D063171:Corneal Pachymetry; D003319:Corneal Stroma / Q000473:pathology; D019781:Corneal Topography; D003430:Cross-Sectional Studies; D019573:Epithelium, Corneal / Q000473:pathology; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007640:Keratoconus / Q000145:classification* / Q000175:diagnosis*; D008297:Male; D018613:Microscopy, Confocal; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence / Q000379:methods*; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult