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Hetal Patel, Bernard Gilmartin, Robert Cubbidge, Nicola Logan; In Vivo Ballistic Measurement Of Anterior Scleral Resistance In Humans. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6312.
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© ARVO (1962-2015); The Authors (2016-present)
Anterior scleral resistance measured with Schiotz indentation tonometry has previously been reported to exhibit regional variation (Patel IOVS 2009, 50, ARVO E-Abstract 3947). These findings require corroboration as Schiotz tonometry uses transformation algorithms that are based on empirical data taken from the cornea. Therefore we examine scleral resistance using ballistic rebound tonometry (RBT) calibrated systematically with reference to agarose biogels of varying Young’s moduli. Given its relevance to the aetiology of myopia scleral resistance is evaluated across 3 ethnic groups that vary in their propensity to myopia.
Scleral resistance was assessed using a table-mounted iCare tonometer (TA01, Tiolat-Oy) to measure 8 scleral regions (nasal, temporal, superior, inferior, inferior-nasal, inferior-temporal, superior-nasal and superior-temporal) at a location 4 mm from the limbus in both eyes. Eye order and sequence of measurement was randomised; each region was assessed twice and 4 valid iCare readings were recorded for each location. The data were collected from young adults of British White (BW) and British South Asian (BSA) [MSE (D) 37 non-myopes (≥-0.50) +0.49±1.08; 38 myopes (<-0.50) -4.70±4.14] descent in the UK and of Hong Kong Chinese (HKC) [MSE (D) 11 non-myopes +0.39±0.66; 49 myopes -4.46±2.70] descent in Hong Kong. Biometric data were compiled using autorefraction and the Zeiss IOLMaster. One- and two-way repeated measures ANOVAs tested regional differences for iCare values across both refractive status and ethnicity.
The RBT calibration procedure demonstrated iCare values to be significantly influenced by the Young’s modulus (E) of the agarose gels, confirming iCare measurements of rigidity to be robust. Significant regional variations in scleral resistance were identified for the BW-BSA (p<0.001) and HKC (p<0.001) individuals; superior-temporal region showed the lowest levels of resistance whilst the inferior-nasal region showed the highest. In comparison to the BW-BSA group, the HKC subjects displayed a significant increase in mean resistance for each respective quadrant (p<0.001). Mean refractive group differences were insignificant.
Data support the previous findings of regional variation in anterior scleral rigidity with the Schiotz tonometer. Furthermore scleral resistance was found to be greater in the HKC group than in the BW-BSA group suggesting that higher levels of anterior scleral resistance may be a correlate of the increased prevalence of myopia in East Asian populations.
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