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Ethnic differences in higher-order aberrations: Spherical aberration in the South East Asian Chinese eye

Lim KL, Fam HB

J Cataract Refract Surg, 2009 Dec;35(12):2144-8.
PMID: 19969221 DOI: 10.1016/j.jcrs.2009.06.031

PURPOSE: To determine the distribution of higher-order corneal and ocular aberrations in a healthy refractive surgery population.
SETTING: Island Hospital, Penang, Malaysia.
METHODS: In this prospective observational study, 1 eye of ethnic Chinese refractive surgery patients was evaluated with an Orbscan II corneal topographer and a Zywave Hartmann-Shack aberrometer with a 6.0 mm pupil. Height data were analyzed to derive the higher-order aberrations (HOAs) from the 3rd to 5th Zernike order.
RESULTS: The mean spherical equivalent in the 70 eyes evaluated was -6.46 diopters +/- 3.10 (SD). The mean total corneal HOA was 0.574 +/- 0.218 microm (range 0.269 to 1.249 microm) and the mean total ocular HOA, 0.525 +/- 0.354 microm (range 0.138 to 2.145 microm). There was no statistically significant correlation with age. The mean 3rd-order ocular aberration was 0.399 +/- 0.287 microm; the mean 4th-order, 0.297 +/- 0.223 microm; and the mean 5th-order, 0.108 +/- 0.101 microm. Corneal spherical aberration was greater than ocular spherical aberration (mean 0.312 +/- 0.114 microm versus 0.200 +/- 0.170 microm). Multilinear regression showed that the only dependent that predicted ocular spherical aberration was anterior corneal asphericity (r(2) = 0.227, F = 17.95, P
Corneal elevation indices in normal and keratoconic eyes

Fam HB, Lim KL

J Cataract Refract Surg, 2006 Aug;32(8):1281-7.
PMID: 16863962 DOI: 10.1016/j.jcrs.2006.02.060

PURPOSE: To determine an index that distinguishes keratoconus and keratoconus-suspect eyes from normal eyes with Orbscan (Bausch & Lomb) corneal elevation maps.
SETTING: Department of Ophthalmology, Tan Tock Seng Hospital, Singapore, and iLaser Centre, Island Hospital, Penang, Malaysia.
METHODS: In this initial phase of this multicenter nonrandomized retrospective study, 1 eye of 166 normal subjects, 15 keratoconus patients, and 11 keratoconus suspects was examined at 1 clinic. The anterior best-fit sphere (BFS), posterior BFS, anterior elevation, posterior elevation, and maximum and minimum keratometries were analyzed. Two indices with the highest sensitivity and specificity classifying these conditions were identified using receiver operating characteristic curves. These 2 indices were evaluated in a subsequent validation study using 1 eye of 221 normal subjects, 43 keratoconus patients, and 23 keratoconus suspects from another clinic.
RESULTS: The anterior elevation and anterior elevation ratio (anterior elevation ratio = anterior elevation/anterior BFS) best classified the different groups. An anterior elevation ratio of 0.5122 mm or less had 99% sensitivity and 95.2% specificity while a ratio 16.5 mum or less had 80.1% sensitivity and 80.8% specificity in discriminating normal eyes from keratoconus and keratoconus suspects. The results were similar in the validation study. In addition, these anterior elevation and anterior elevation ratio cutoff values had high sensitivity and specificity in identifying keratoconus suspects from normal eyes in the validation study.
CONCLUSION: Anterior corneal elevation parameters are clinically relevant measures for detecting keratoconus and suspected keratoconus eyes.
Relationship between the corneal surface and the anterior segment of the cornea: An Asian perspective

Lim KL, Fam HB

J Cataract Refract Surg, 2006 Nov;32(11):1814-9.
PMID: 17081863

To determine the values for the anterior best-fit sphere (BFS) and posterior BFS in an Asian population using the Orbscan II (Bausch & Lomb) slit-scanning Placido disk corneal topographer.
NeuroVision treatment for low myopia following LASIK regression

Lim KL, Fam HB

J Refract Surg, 2006 Apr;22(4):406-8.
PMID: 16629076

PURPOSE: To evaluate a novel non-surgical method for improving vision in a refractive surgery patient.
METHODS: A 45-year-old man who had undergone LASIK 5 years previously presented with blurred distance vision. Unaided vision in the right eye was 20/329-2) and 20/20 in the left eye. He enrolled for NeuroVision treatment (NeuroVision Pte Ltd, Singapore), a computer-based interface in which a repetitive set of visual excerises is performed for 10 to 12 weeks.
RESULTS: After 35 sessions, unaided visual acuity in the right eye was 20/16(-3) and 20/20(-1) in the left eye, representing 2.8 lines of improvement in the right eye and 1.6 lines in the left eye.
CONCLUSIONS: NeuroVision, a noninvasive treatment based on the concept of perceptual learning, is a benefit in cases in which surgical enhancement is not recommended.