Authors: Sangsu Han, Nirojini Sivachandran, Mark Fava
Author Disclosure Block: S. Han: None. N. Sivachandran: None. M. Fava: None.

Abstract Body:

Purpose: Although it is well-known that keratoconus (KCN) often presents with normal clinical findings in its early stages, it is unclear how early/late into the disease process these patients are diagnosed with KCN. Our goal is to determine the stage of KCN at first presentation with an ophthalmologist. The Amsler Krumeich (AK) classification, and the “Keratoconic cone (K_Max)-Decentration of the thinnest pachymetry from the apex-Thinnest pachymetry” (KDT) classification were used.
Study Design: A single-centered retrospective chart review.
Methods: We reviewed the charts of all patients referred for KCN at the Hamilton Regional Eye Institute from 2013 to 2017. Demographics (age, gender), best corrected visual acuity (BCVA), slit lamp examination (SLE) findings, refraction, and corneal topography (keratometry, pachymetry, astigmatism) with the Oculus Pentacam were obtained. For the eyes that we newly diagnosed with KCN, we used the AK and KDT classifications to stage the disease.
Results: Out of 154 patients referred for KCN, 133 (86%) had positive diagnoses. 119/133 (89%) were newly diagnosed with KCN. The mean age at diagnosis was 30.4 ± 10.2 years while the mean BCVA was 0.42 ± 0.57 on LogMAR scale. The SLE findings associated with KCN were present in only 66/238 (28%) eyes. The 238 eyes with new diagnoses of KCN were divided into: 138 (58.0%) Stage 1, 51 (21.4%) Stage 2, 22 (9.2%) Stage 3, and 27 (11.3%) Stage 4 based on the AK classification. Calculation of the mean values yielded the average AK classification to be Stage 1. With regards to the KDT classification, the mean K_Max was 55.2 ± 10.1 diopters, the mean decentration of the thinnest pachymetry from the apex was 0.91 ± 0.31 mm, and the mean thinnest pachymetry was 471.6 ± 55.7 um; this translated into mean KCN stage of K2D2T1. “K” and “T” parameters of the KDT classification showed significant positive correlations to the AK classification (Pearson Chi-Square, p<0.000 and p<0.000). In the meantime, “D” parameter showed significant negative correlation to the AK classification (Pearson Chi-Square, p<0.013).
Conclusions: We reinforce the results of previous studies by demonstrating that majority of the eyes with early KCN have unremarkable SLE findings. We add to the literature by showing that KCN patients usually present themselves for ophthalmological assessment at Stage 1 based on AK classification, or at Stage K2D2T1 based on KDT classification. While the KDT classification is generally in good agreement with the AK classification, its slightly higher staging may be attributable to it utilizing the corneal topography data better. The AK classification, which is from the pre-corneal topography era, fails to incorporate the data available through corneal topography. To summarize, we highlight the important role of corneal topography as an essential diagnostic modality for early detection of KCN.