1. 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, EY and an unrestricted grant from the Research to Prevent Blindness, New York, New York.

2. 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

3. 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™.

4. 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.

5. Methods
The Amsler-Krumeich classification1 includes the following stages:
Stage I
Eccentric steeping
Myopia and astigmatism < 5.00 D
Mean central K readings < D
Stage II
Myopia and astigmatism from 5.00 to 8.00 D
Mean central K readings < D
Absence of scarring
Minimum corneal thickness >400 µm.
Stage III
Myopia and astigmatism from 8.00 to 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

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

7. 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

8. 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

9. 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.

10. Results

11. 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.