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J. L. Alio, S. Patel, F. Amparo, D. Piñero; Clinical Performance of an Automated Device (vch-1) to Determine Tissue Water Content and Refractive Index in vivo During Refractive Surgery. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4201.
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To, I) compare the performance of the VCH-1 (a digital surgical hydrometer based on Abbé refractometry) in vitro with a standard bench model refractometer (BR). II) investigate the influence of age and duration of excimer laser photoablation on the refractive index (RI) and estimated hydration of the human corneal stroma in vivo.
I) the refractive index of a range of 7 turbid semi-liquid media (gels, soaps, creams) were measured using VCH-1 & BR at room temperature. II)RI & hydration (estimated using Fatt-Harris equation) of the stromal bed was determined after lifting the flap (created using a femtosecond laser, IntralaseTM) prior to, and immediately after, photoablation for LASIK (achieved using Schwind EsirisTM platform) in neophytes listed for unremarkable surgery over a range of refractive errors. Patient’s age(x years) and duration of photoablative treatment (t secs) was recorded.
(I) Mean RMS difference between refractive index estimates according to VCH-1 and BR was 0.0029 units. II) Mean RI (±s.d) values before and after photoablation were 1.3718 (±0.0006) & 1.3799 (±0.0094). III) A significant relationship was found between a] age & refractive index (R1 = 1.36524+0.00019x, r=+0.347,n=45, one eye/patient, p=0.010), b]change in RI (ΔRI) and t, (ΔRI = 0.0054+0.00016t, r=+0.4639,n=74, all eyes, p<0.0001).
VCH-1 is a rapid safe technique for estimating RI and tissue water content (WC). Stromal RI increases with age suggesting, 1.1% fall in WC per decade. On average, photoablation resulted in 4.8% fall of stromal WC at an approximate rate of 2.9% per 30 seconds of photoablative treatment
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