Abstract
Anterior segment optical coherent tomography (AS-OCT, Visante; Zeiss) is used to examine meridional variation in anterior scleral thickness (AST) and its association with refractive error, ethnicity and gender. Scleral cross-sections of 74 individuals (28 males; 46 females; aged between 18-40 years (27.7±5.3)) were sampled twice in random order in 8 meridians: [superior (S), inferior (I), nasal (N), temporal (T), superior-temporal (ST), superior-nasal (SN), inferior-temporal (IT) and inferior-nasal (IN)]. AST was measured in 1mm anterior-to-posterior increments (designated the A-P distance) from the scleral spur (SS) over a 6mm distance. Axial length and refractive error were measured with a Zeiss IOLMaster biometer and an open-view binocular Shin-Nippon autorefractor. Intra- and inter-observer variability of AST was assessed for each of the 8 meridians. Mixed repeated measures ANOVAs tested meridional and A-P distance differences in AST with refractive error, gender and ethnicity. Only right eye data were analysed. AST (mean±SD) across all meridians and A-P distances was 725±46μm. Meridian SN was the thinnest (662±57μm) and I the thickest (806±60μm). Significant differences were found between all meridians (p<0.001), except S:ST, IT:IN, IT:N and IN:N. Significant differences between A-P distances were found except between SS and 6 mm and between 2 and 4 mm. AST measurements at 1mm (682±48 μm) were the thinnest and at 6mm (818±49 μm) the thickest (p<0.001); a significant interaction occurred between meridians and A-P distances (p<0.001). AST was significantly greater (p<0.001) in male subjects but no significant differences were found between refractive error or ethnicity. Significant variations in AST occur with regard to meridian and distance from the SS and may have utility in selecting optimum sites for pharmaceutical or surgical intervention.
Highlights
IntroductionInformation on the properties of scleral tissue is apposite to our understanding of the aetiology of myopia [1], glaucoma [2], age-related macular degeneration (AMD) [3], surgical procedures [4,5] and the pharmacokinetics of drug transmission to the posterior globe [6,7].A specific and accessible property of sclera tissue, anterior scleral thickness (AST), has previously been determined in vivo for specific meridians using ultrasound biometry (UBM) [8,9,10], ultrasound pachymetry [11] and anterior segment optical coherent tomography [12,13]
Independent Student’s t test analyses revealed no significant difference in ocular biometric parameters (i.e. MSE, axial length (AL), Central corneal thickness (CCT), anterior chamber depth (ACD) and corneal curvature) for either gender or ethnicity
A significant difference (p
Summary
Information on the properties of scleral tissue is apposite to our understanding of the aetiology of myopia [1], glaucoma [2], age-related macular degeneration (AMD) [3], surgical procedures [4,5] and the pharmacokinetics of drug transmission to the posterior globe [6,7].A specific and accessible property of sclera tissue, anterior scleral thickness (AST), has previously been determined in vivo for specific meridians using ultrasound biometry (UBM) [8,9,10], ultrasound pachymetry [11] and anterior segment optical coherent tomography [12,13]. Much of the previous literature concerning intra-individual and inter-individual variation in AST has concerned individuals with myopia [9, 16] or glaucoma [10, 13]. In their UBM study, Oliveira et al, [9] found thickness along the anterior temporal meridian to correlate positively with increasing axial length (AL) and myopic refractive error but this was not corroborated by Yoo et al, [13]. Data on differences in scleral thickness between ethnic groups appears to be confined to Caucasian and non-Caucasian individuals, the former having thinner temporal sclera thickness [9]
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