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Higher-Order Wavefront Aberration and Letter-Contrast Sensitivity In Eye (2008) 22, 1488–1492 & 2008 Macmillan Publishers Limited All rights reserved 0950-222X/08 $32.00 www.nature.com/eye 1 1 2 2 CLINICAL STUDY Higher-order C Okamoto , F Okamoto , T Samejima , K Miyata and T Oshika1 wavefront aberration and letter-contrast sensitivity in keratoconus Abstract Keywords: keratoconus; wavefront aberration; higher-order aberration; contrast sensitivity; Aims To evaluate the relation between letter-contrast sensitivity higher-order aberration of the eye and contrast sensitivity function in eyes with keratoconus. Methods In 22 eyes of 14 patients with Introduction keratoconus (age 30.578.4 years, means7SD) and 26 eyes of 13 normal controls (age Keratoconus is a chronic, non-inflammatory 29.276.7 years), ocular higher-order wavefront disease of the cornea associated with aberration for a 6-mm pupil was measured progressive thinning and anterior protrusion of with the Hartmann-Schack aberrometer the central cornea.1,2 Irregular astigmatism is (KR-9000 PW, Topcon). The root mean square often the first and most apparent clinical finding (RMS) of third- and fourth-order Zernike in keratoconus, and this is evidenced by a coefficients was used to represent higher-order distortion of the corneal image as noted with aberrations. The letter-contrast sensitivity was the placido disc, retinoscope, keratometer, examined using the CSV-1000LV contrast chart keratoscope, and computerized (Vector Vision). videokeratograph. Previous studies using Results In the keratoconus group, the videokeratography have quantitatively 1 Department of letter-contrast sensitivity showed significant demonstrated that corneal irregular Ophthalmology, Institute of correlation with third-order (Spearman’s astigmatism is significantly greater in eyes with Clinical Medicine, University correlation coefficient ¼À0.736, 0.001) 3–6 of Tsukuba, Ibaraki, Japan r Po keratoconus than in normal eyes. In addition, and fourth-order aberrations (r ¼À0.464, recent studies using wavefront analysis 2Meiwakai Miyata Eye Po0.05). There was borderline correlation technology showed that ocular and corneal Hospital, Miyazaki, Japan between log MAR BSCVA and third-order higher-order aberration, particularly coma (r ¼ 0.413, P ¼ 0.070) and fourth-order aberration, is significantly increased in Correspondence: T Oshika, aberrations (r ¼ 0.394, P ¼ 0.086). In the keratoconus.7–10 Maeda et al11 reported that Department of normal group, the letter-contrast sensitivity corneal topographic indices significantly Ophthalmology, had no significant correlation with Institute of Clinical correlated with letter-contrast sensitivity in eyes 7 Medicine, third-order (r ¼À0.170, P ¼ 0.411) and with keratoconus. Applegate et al reported University of Tsukuba, fourth-order aberrations (r ¼À0.088, P ¼ 0.673), significant correlation between corneal 1-1-1 Tennoudai, and log MAR best spectacle-corrected visual aberration and contrast sensitivity in 91 eyes Tsukuba, Ibaraki 305-8575, acuity (BSCVA) showed no correlation with a variety of corneal conditions, including Japan with third-order (r ¼ 0.063, P ¼ 0.762) Tel: þ 81 29 853 3148; 8 eyes with keratoconus, but such correlation in Fax: þ 81 29 853 3148. and fourth-order aberrations (r ¼À0.282, eyes with keratoconus was not assessed. To the E-mail: toshika@ P ¼ 0.165). best of our knowledge, the influence of ocular md.tsukuba.ac.jp Conclusions In eyes with keratoconus, there higher-order aberration on contrast sensitivity is significant correlation between contrast function in eyes with keratoconus has not Received: 11 April 2007 sensitivity and ocular higher-order wavefront been investigated. We conducted the current Accepted in revised form: aberrations. 15 May 2007 study to investigate the relationship between Published online: 8 June Eye (2008) 22, 1488–1492; doi:10.1038/sj.eye.6702902; ocular wavefront aberration and 2007 published online 8 June 2007 letter-contrast sensitivity in keratoconus. Aberration and contrast sensitivity in keratoconus C Okamoto et al 1489 Methods Table 1 Measurement results We examined 22 eyes of 14 patients with keratoconus. Keratoconus Normal controls There were seven men and seven women, and their age m 7 7 7 Third-order aberration ( m) 1.585 0.799* 0.252 0.119 averaged 30.5 8.4 years old. They were diagnosed with Fourth-order aberration (mm) 0.48770.181* 0.17070.100 slit lamp biomicroscopy and corneal videokeratography. log MAR BSCVA 0.03770.169* À0.11870.063 Eyes with corneal scarring or cataract were excluded Letter-contrast sensitivity 17.473.8* 21.871.4 from the subjects. The best spectacle-corrected visual BSCVA, best spectacle-corrected visual acuity. acuity (BSCVA) ranged from 25/20 to 20/40. Twenty-six Mean7SD. eyes of 13 patients served as age-matched normal *Po0.0001: significantly different from that of normal controls (Wilcoxon rank-sum test). controls. There were eight men and five women, and their age averaged 29.276.7 years old. The BSCVA was 20/20 or better. Ocular wavefront aberrations for 6-mm pupils were measured using a Hartmann–Shack wavefront analyser (KR-9000 PW, Topcon Corp., Tokyo, Japan) after the pupils were fully dilated with 1% tropicamide. Measurements were repeated three times for each subject, and the mean of the measurements was used for data analyses. All of the Hartmann images were revised to the pupil centre images.12–14 The obtained data were expanded into the set of orthogonal Zernike polynomials. The root mean square of third-order À3 3 À4 4 (Z3 to Z3) and fourth-order (Z4 to Z4) Zernike components were used to represent higher-order aberrations.15–19 Figure 1 There was borderline correlation between log MAR Letter-contrast sensitivity was measured with BSCVA and third-order aberration (Spearman’s correlation CSV-1000LV chart (Vector Vision, Columbus, OH, USA). coefficient r ¼ 0.413, P ¼ 0.07) in eyes with keratoconus. This instrument uses letter optotypes all of which were the same size and of low spatial frequency (2.4 cycle/1).20 worse in eyes with keratoconus (0.03770.169) than in There were eight contrast levels (standard, 35.5, 17.8, 8.9, the normal controls (À0.11870.063) (Po0.001). The 6.3, 4.5, 2.2, and 1.1%), and each contrast level had three letter-contrast sensitivity was significantly lower in eyes letters. The measurements were performed at 2.5 m with keratoconus (17.473.8 letters) than in the normal distance under full spectacle correction. The mean controls (21.871.4 letters) (Po0.0001). A total of 5 out luminance was 81 cd/m2. The test results were recorded, of 26 eyes (19.2%) in the normal group could read all not as the contrast threshold or contrast sensitivity, 24 letters, while no eye in the keratoconus group scored but as the number of correctly identified letters out full marks. of 24 letters.11,21 The relation between visual function and The study followed the tenets of the Declaration of higher-order aberration was evaluated. In the Helsinki, and prestudy informed consent was obtained keratoconus group, there was borderline correlation from all subjects after explanation of the nature and between log MAR BSCVA and third-order (Spearman’s possible consequences of the study. The patients with correlation coefficient r ¼ 0.413, P ¼ 0.070; Figure 1) and keratoconus were instructed to refrain from wearing fourth-order aberrations (r ¼ 0.394, P ¼ 0.086; contact lenses for at least 2 weeks before the study Figure 2). The letter-contrast sensitivity showed examinations. A single experienced investigator significant correlation with third-order (r ¼À0.736, performed all measurements. Po0.001; Figure 3) and fourth-order aberrations (r ¼À0.464, Po0.05; Figure 4). In the normal group, there was no significant Results correlation between log MAR BSCVA and third-order Measurement results are shown in the Table 1. The eyes (r ¼ 0.063, P ¼ 0.762) and fourth-order aberrations with keratoconus showed significantly larger values than (r ¼À0.282, P ¼ 0.165). The letter-contrast sensitivity the normal controls in both third-order (Po0.0001, also showed no significant correlation with third-order Wilcoxon rank-sum test) and fourth-order aberrations (r ¼À0.170, P ¼ 0.411) and fourth-order aberrations (Po0.0001). The log MAR BSCVA was significantly (r ¼À0.088, P ¼ 0.673). Eye Aberration and contrast sensitivity in keratoconus C Okamoto et al 1490 Discussion Our study showed that ocular third- and fourth-order aberrations were significantly larger in eyes with keratoconus than in the normal controls. Previous studies also reported that coma and spherical aberrations significantly increased in eyes with keratoconus, with larger increases in coma aberration.7–10 Maeda et al8 found that coma aberration was 2.32 times larger than spherical aberration in eyes with keratoconus, and Barbero et al9 reported that coma aberration was 3.74 times higher in eyes with keratoconus than in normal controls. In the current study, third-order coma aberration was 3.25 times larger than fourth-order Figure 2 There was borderline correlation between log MAR spherical aberration in eyes with keratoconus, and BSCVA and fourth-order aberration (Spearman’s correlation third-order aberration was 6.29 times higher in eyes coefficient r ¼ 0.394, P ¼ 0.086) in eyes with keratoconus. with keratoconus than in the normal controls. We found that letter-contrast sensitivity was significantly deteriorated in eyes with keratoconus, and both third- and fourth-order aberrations showed significant correlation with letter-contrast sensitivity. In normal controls, letter-contrast sensitivity did not correlate with either third- or fourth-order aberrations. In the CLEK study, it has been reported that low-contrast acuity deteriorated more rapidly than high-contrast visual acuity in eyes with keratoconus.22 Pesudovs et al23 demonstrated that while visual acuity is an excellent test for comparing normal, keratoconus, and post-penetrating keratoplasty groups, additional useful information can be provided by low-contrast visual acuity and Pelli-Robson contrast sensitivity.
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