Corneal High-Order Aberrations in Keratoconus Juan C. Arciniega, MD; Engy M. Mohamed, MD; R. Wayne Bowman, MD; Steven Verity, MD; James P. McCulley, MD, FRCOphth (UK). Department of Ophthalmology, The University of Texas Southwestern Medical Center at Dallas, Texas. USA. Financial Disclosure: Juan C. Arciniega, Engy M. Mohamed, Steven Verity and R. Wayne Bowman have no commercial relationships. James P. McCulley is a consultant of Alcon Inc. This study was supported in part by grants NIH EY12430, EY016664 and an unrestricted grant from the Research to Prevent Blindness, New York, New York.

Background Keratoconus is a condition in which the cornea assumes a conical shape as a result of non-inflammatory progressive corneal thinning. The thinning and protrusion in keratoconus induces irregular astigmatism with and without myopia resulting in mild to marked impairment in both quantity and quality of vision. It is a progressive disease ultimately affecting both eyes, although only one eye may be affected initially.1 Kanski Jack, Clinical Ophthalmology. Sixth edition, Elsevier, 2007

Purpose To evaluate the use of the anterior and posterior corneal surface high-order aberrations (HOAs) as a tool to detect and grade keratoconus using the Pentacam™.

Methods A retrospective study of 111 eyes (62 patients; 33 males) was performed. The eyes were divided into 5 groups: suspect group and four other groups according to the Amsler-Krumeich classification of keratoconus: stage I to stage IV groups. Anterior and posterior corneal HOAs were obtained using the software provided by the Pentacam™ system.

Methods The Amsler-Krumeich classification1 includes the following stages: Stage I Eccentric steeping Myopia and astigmatism < 5.00 D Mean central K readings < 48.00 D Stage II Myopia and astigmatism from 5.00 to 8.00 D Mean central K readings < 53.00 D Absence of scarring Minimum corneal thickness >400 µm. Stage III Myopia and astigmatism from 8.00 to 10.00 D Mean central K readings >53.00 D Minimum corneal thickness 300 to 400 µm. Stage IV Refraction not measurable Mean central K readings >55.00 D Central corneal scarring Minimum corneal thickness 200 µm Alió Jorge, Corneal Higher Order Aberrations: A Method to Grade Keratoconus. J Refract Surg. Vol. 22   No. 6   June 2006

Methods Anterior & Posterior Zernike (Z) coefficients were used from Z3 to Z6 to calculate: Coma-like aberration Spherical-like aberration Residual aberrations

Results The mean age of patients was 49.4±6.7 years. The mean keratometric value was 43.30±14 D The mean thinnest point of corneal thickness was 450.8±87µm. Number of Patients 62 Eye number 111 Right eye 58 Left eye 53 Males 33 Females 29 Stage I 43 Stage II 24 Stage III 8 Stage IV 21 Suspect 15

Mean keratometric value Results Patients Demographics Suspect Stage I Stage II Stage III Stage IV Age 41.9±18.5 44.5±11.8 41.9±16.6 43.1±15.9 43.9±12 Mean keratometric value 43.6±1.9 44.8±1.9 49.9±1.4 53.8±0.55 60.5±5.3 Corneal thickness 519.8±40.6 490.4±44.4 437.2±45.1 413.6±74.1 349.9±117 Sphere -4.4±3.3 -5.1±3.5 -9.7±3.2 -8.7±3.7 -9.7±4.7 Cylinder 2.3±1.4 3.5±1.9 2.6±2.5 4.5±1.8 4.5±3 Spherical equivalent -3.2±3.1 -3.4±3.4 -5.5±3.3 -6.5±4 -7.4±4

Results Posterior coma-like aberration was the highest posterior HOAs among all the groups and anterior coma-like aberration was the highest of anterior HOAs among all groups except for the suspect group which had the anterior spherical-like aberration as the highest. Anterior coma-like aberrations increased progressively with the groups while the posterior coma-like aberrations did not show a gradually increase.

Results

Conclusion Corneal higher-order aberrations, especially coma-like aberrations, are significantly higher in eyes with keratoconus than in keratoconus suspects. Only anterior coma-like aberrations measured by Pentacam™ were best in the early detection and grading of keratoconus.