Abstract
With the development of rigid gas permeable materials there has been a re-emergence in the use of scleral lenses in managing a wide range of ocular conditions including high myopia, corneal irregularities and various ocular surface pathologies. Scleral lenses rest on the bulbar conjunctiva over the sclera, with the landing zone being the only point of contact with the ocular surface. Proper alignment of the landing zone with the scleroconjunctival surface is essential for optimal fit, as improper fitting can lead to complications such as corneal oedema, staining, epithelial damage, or conjunctival prolapse. Accurate scleral topography measurements are, therefore, vital to mitigate these issues, as they allow a better understanding of the close interaction between the lens and corneal and scleral surface.
Scleral topography involves mapping of the scleral surface by measuring various metrics of the scleral contour like sagittal height, scleral angles and radius of curvature. The sclera, forming 80% of the outer layer of the eye, provides structural support and enables controlled eye movement. However, its asymmetrical nature, with temporal areas often steeper than nasal ones, complicates scleral lens fitting. Racial variations in scleral properties and other ocular parameters have been documented in previous studies emphasising the importance of establishing race-specific normative data for scleral topography. Such data are crucial for enabling customised lens fittings, ultimately enhancing visual outcomes. For instance, African sclerae are stiffer and age differently compared to Caucasian sclerae, while Chinese eyes exhibit distinct corneal flattening patterns when wearing miniscleral lenses. Despite these findings, there remains a notable gap in data on scleral topography of the eyes of African people.
The aim of this study was to establish baseline data on the scleral topography of African eyes, providing descriptive statistics and exploring correlations with axial length, refractive error, and corneal parameters. Additionally, it compared African scleral topography with published data on Caucasian and Asian populations to highlight racial differences in scleral anatomy. A total of 90, 70 male and 20 female, healthy participants of African descent aged between 18 to 41 years (mean age 24.6 years) were recruited for this study. The Pentacam AXL Wave, a scheimpflug imaging system, was used to capture scleral topography measurements and other refractive and ocular biometric measurements required for the study.
The results of this study presented normative data on the scleral topography of African eyes, providing a foundation for understanding the unique characteristics of this population. The findings provided a detailed understanding of the scleral profile in terms of sagittal height, bulbar slope, scleral toricity and scleral asymmetry. The mean sagittal height increased from 2082 ± 103 μm at the 11 mm chord to 4454 ± 247 μm at the 17 mm chord. The mean scleral asymmetry was the greatest along the horizontal meridian increasing from 263 ± 126 μm at the 11 mm chord to 1393 ± 276 μm at the 17 mm chord confirming the asymmetrical nature of the sclera as reported in previous studies. Correlation analysis revealed the strongest negative association between axial length and sagittal height along the temporal meridian across all chords (p <0.001), giving further insights into scleral changes that take place during myopia development. Similarly, objective refraction exhibited statistically significant correlations with scleral sagittal height and scleral asymmetry, particularly when the sample was divided into myopic and emmetropic groups, highlighting refractive status as a differentiating factor in scleral topography. Additionally, corneal parameters showed notable correlations with scleral measures, along with a brief power vector analysis, which provided deeper insight into these interrelationships.
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The study demonstrated that the sclerae of African eyes exhibit distinct topographical features when compared to Caucasian and Chinese populations, characterised by flatter and more toric scleral profiles with greater scleral asymmetry. Additionally, the statistically significant correlations between axial length and refractive error offer valuable clinical insights into the scleral changes associated with myopia development. Lastly, the observed associations between corneal and scleral parameters highlight an integrated relationship between these anatomically distinct ocular structures.