Spherical Equivalent Refraction (spherical_equivalent + refraction)

Distribution by Scientific Domains

Selected Abstracts

Refractive error and ocular biometry in Jordanian adults

Edward A. H. Mallen
Abstract The aim of this study was to establish the prevalence of refractive errors in Jordanian adults of working age, and to study the ocular biometric correlates of refractive error in this population. Refractive error and ocular biometry were measured in 1093 Jordanian adult subjects aged 17,40 years to determine the prevalence of refractive error, and explore structural correlations of ametropia. Refractive error was measured using a Grand-Seiko GR-3100K closed-view infrared autorefractor. Ocular component measurements were made using A-scan ultrasonography and autokeratometry. The prevalence of myopia [spherical equivalent refraction (SER) less than ,0.50 DS] and hyperopia (SER greater than +0.50 DS) was 53.71 and 5.67% respectively; 40.62% of the sample was emmetropic (refraction between +0.50 D and ,0.50 D inclusive in both principal meridians). The distribution of SER was found to show marked leptokurtosis, exhibiting a peak between plano and 1 D of myopia. Corneal radius, anterior chamber depth, crystalline lens thickness, vitreous chamber depth and axial length (AL) parameters were normally distributed in the population studied. AL to corneal curvature ratio was not normally distributed, and showed marked leptokurtosis. Linear regression analysis showed that AL correlated most closely with spherical equivalent refractive error. This study has established a database of refractive error prevalence and ocular biometric correlates of ametropia in a Middle Eastern population of working age. [source]

Lens opacity and refractive influences on the measurement of retinal vascular fractal dimension

Haitao Li
Acta Ophthalmol. 2010: 88: e234,e240 Abstract. Purpose:, To examine the influence of lens opacity and refraction on the measurement of retinal vascular fractal dimension (Df). Methods:, Optic disc photographs (right eyes) of 3654 baseline Blue Mountains Eye Study participants (aged 49,97 ) were digitized. Retinal vascular Df was quantified using a computer-based program. Summated severity scores for nuclear, cortical and posterior subcapsular (PSC) cataract were assessed from lens photographs. Refraction data were converted to spherical equivalent refraction (SER), as sum spherical plus 0.5 cylinder power. Axial length was measured at 10-year follow-up examinations using an IOL master. Results:, Mean Df of the retinal vasculature was 1.444 0.023 for 2859 eligible participants. Increasing lens opacity scores were associated with significant reduction in Df (, = ,0.0030, p < 0.0001). Both cortical and PSC cataract involving central lens area were associated with reduced Df, after controlling for confounding factors (ptrend , 0.0105). Increasing myopia severity was associated with reduced Df after adjusting for lens opacity scores and other confounders (ptrend < 0.0001). The slope of Df decrease per SER reduction was 0.0040 in eyes with SER , ,4D, compared to ,0.0016 in eyes with SER > ,4D. For axial length quintiles, there were no significant differences in mean Df in all groups except a reduction in the fifth quintile (axial length ,24.15 mm) (all p < 0.05). Conclusion:, Ocular media opacity independently influenced retinal vascular Df measurement, but we found no evidence supporting any refractive axial magnification effect on this measure. Myopic refraction ,,4D was associated with a reduction in Df, suggesting rarefaction of retinal vasculature associated with high myopia. [source]

Comparison of two partial coherence interferometers for corneal pachymetry in high myopia and after LASIK

Anders Ivarsen
Abstract. Purpose:, We aimed to compare the Haag-Streit optical low-coherence reflectometry (OLCR) pachymeter and the Zeiss Anterior Chamber Master (ACMaster) for measuring central corneal thickness (CCT) in high myopes and after laser in situ keratomileusis (LASIK) for myopia. Methods:, Central corneal thickness was measured in 55 eyes of 30 myopic subjects (spherical equivalent refraction of , 5.25 D to , 10.75 D, maximal astigmatism of , 2 D), and in 37 eyes of 21 patients 3 months after LASIK for myopia (preoperative spherical equivalent refraction of , 6.0 D to , 10.75 D, maximal astigmatism of , 2 D). All measurements were performed with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster, using group refractive indices of 1.376 and 1.3851, respectively. Thickness measurements were compared using paired t -tests, Pearson's correlation, linear regression and Bland,Altman plots. Results:, In myopic subjects, CCT measured 531 28 ,m and 533 27 ,m with the OLCR pachymeter and the ACMaster, respectively (p < 0.01); all measurements correlated closely (r = 0.99, p < 0.01). In LASIK-treated eyes, CCT measured 472 24 ,m using the OLCR pachymeter and 475 23 ,m using the ACMaster (p < 0.01), again with close correlation between the two instruments (r = 0.99, p < 0.01). Conclusions:, Measurements of CCT in high myopes and after myopic LASIK were very similar with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster. Using the current group refractive indices, the observed difference between the two instruments of < 3 ,m is of little clinical importance. Thus, it would seem safe to use the OLCR pachymeter and the ACMaster interchangeably for CCT measurements in myopia as well as after myopic LASIK. [source]