Anterior corneal elevation parameters are clinically relevant measures for detecting keratoconus and suspected keratoconus eyes.

Modifying the keratometric index increased the accuracy of predicting the posterior corneal power.

Aim: To investigate the association between central corneal thickness (CCT) and the degree of myopia among Chinese. Methods: In this prospective observational study, 714 consecutive patients were recruited from a refractive surgery clinic. CCT was measured in both eyes of each patient using the Orbscan (Bausch and Lomb, Rochester, New York, USA), and data of the right eye were selected for analysis. CCT was correlated with the degree of myopia in dioptres (D) using Pearson's correlation coefficient and Dunnett's t test with multiple comparisons. Results: The age of the patients ranged from 15 to 59 years. The mean CCT was 534.5 mm, with a standard deviation (SD) of 38.1 (range 305-684) mm. M yopia is increasing in prevalence among the populations of East Asian origin. Estimates of the proportion of myopia in the young population of Singapore range from 30% to 65%, 1 2 and the prevalence was found to be greater among the Chinese, 3 4 and to increase with higher educational achievements.3 4 With increasing rates of myopia, refractive surgery such as laser in situ keratomileusis (LASIK) has become popular in Asia. When undertaking such surgery to correct myopia, central corneal thickness (CCT) is an important consideration to prevent the cornea from becoming too thin after treatment.Studies that have attempted to investigate the effect of refractive errors on CCT have reported conflicting results. One report showed no correlation between corneal thickness and the level of myopia, 5 whereas another study found the cornea to be thinner in more myopic eyes. 6 The two studies used different techniques of measuring CCT and there was some variability in the study population. The aim of this study was to prospectively investigate the relationship between CCT and the degree of myopia in a large sample of Asian adults with myopia who were being assessed for refractive surgery. METHODSPatients consisted of 714 consecutive ethnic Chinese refractive surgery candidates who presented at a refractive surgery clinic for LASIK assessment. The institutional review board provided approval for the protocol of this study and written informed consent was obtained from all patients. Exclusion criteria were previous ocular surgery, ocular pathology such as keratoconus or glaucoma, or recent contact lens wear in the previous 2 weeks.Manifest refraction and CCT measurements with the Orbscan II (Bausch and Lomb, Rochester, New York, USA) were carried out on both eyes of all the patients. Only data from the right eyes were used in the analysis. Pearson correlation analysis was carried out to examine the relationship between the degree of myopia and CCT. The Dunnett t test (two-sided) multiple comparisons were used to compare CCT among the classes of myopes, such as 0 to -4 D, 24 to -8 D and .-8 D, with the last group being used as the test group. A similar comparison was made of the degree of myopia among CCT groups, such as those ,500 mm, 500-550 mm, 550-600 mm and .600 mm. Data were analysed using SPSS V.11.0, and significance was assumed a...

Orbscan is capable of giving repeatable pachymetry readings that are comparable to the ultrasound pachymeter within the central and thinnest point of the cornea. There is a gradual loss of repeatability toward the peripheral cornea possibly as a result of a lack of overlapping data points.

There was a close relationship between the various corneal parameters, which is significant in refractive surgery and intraocular lens calculation and design.