PurposeThe purpose of this study was to compare the precision and accuracy of commercially available tear film osmometers.MethodsContrived tear solution target values representing the physiological range of tear osmolarity (normal eyes 297 mOsm/L, moderately dry eyes 342 mOsm/L, and severe dry eyes 383 mOsm/L) were constructed using a mix of mono- and divalent electrolytes, metabolites, serum albumin, and pH balanced to 7.4. Solution values were randomized and masked from the investigators during testing. Osmometers (Wescor 5520 Vapro Pressure Osmometer: device A, TearLab Osmolarity System: device B, and i-Med Pharma i-Pen: device C) were calibrated according to manufacturer instructions. Each level was tested 64× on each osmometer across two sites. Accuracy was reported as a correlation coefficient against expected linear dilutions, precision was calculated as percent coefficient of variation.ResultsDevice A reported a correlation with known solutions of r2=0.98, with averages of 305.6±4.0, 352.2±5.5, and 389.8±4.0 mOsm/L, and coefficient of variations (CVs) of 1.3%, 1.6%, and 1.0%, respectively. Device B reported an r2=0.96, with averages of 300.6±3.7, 341.4±7.9, and 376.8±5.1 mOsm/L, and CVs of 1.2%, 2.3%, and 1.4%, respectively. Device C reported an r2=0.03, with averages of 336.4±21.5, 342.0±20.7, and 345.7±22.0 mOsm/L, and CVs of 6.4%, 6.1%, and 6.4%, respectively.ConclusionIn this randomized, masked, in vitro study, device A and device B had significantly better accuracy and precision in measuring osmolarity of contrived tear solutions of known target values compared to device C. Device C showed insufficient performance to accurately and precisely delineate osmolarity levels in the physiological range. Furthermore, in vivo studies would be required to compare performance in human subjects.
Purpose:To evaluate the validity and reliability of a novel handheld osmolarity system (I-PEN Osmolarity System; I-MED Pharma Inc, Dollard-des-Ormeaux, Quebec, Canada) for measurement of the osmolarity of a National Institute of Standards and Technology (NIST) traceable solution at a variety of ambient temperatures.Methods:A total of 65 measurements of an NIST solution with a verified osmolarity of 290 ± 2 mOsmol/L were taken using 3 separate handheld osmolarity systems, 65 unique single-use sensors (SUSs) from 3 different lots, and 2 adaptors. Mean values were calculated using the device, SUS, and adaptor. Measurements were taken using a handheld osmolarity system, an adaptor, and 56 individual SUSs at 6 different ambient temperatures ranging from 17.7 to 26.5°C.Results:Overall, the mean osmolarity measured was 294.06 mOsmol/L (SD ±2.29; percent coefficient of variation 0.78), ranging from 286.60 to 298.18 mOsmol/L. This fell within a prespecified acceptable variability of ±4 mOsmol/L (SD ±7). Mean values did not vary across devices, adaptors, or single-use sensors used. Mean osmolarity measurements increased with rising ambient temperatures, with an R2 = 0.88. The temperature correction factor was calculated to be 2.01 mOsmol/L per °C.Conclusions:The osmolarity system reliably and accurately measured the osmolarity of an NIST solution in a laboratory setting, using an adaptor to correct for differences in resistance between a laboratory NIST solution measurement and direct measurements on the palpebral conjunctiva of the eyelid. The handheld osmolarity system represents a rapid and accurate instrument for measurement of tear osmolarity in a simulated testing setting.
Purpose: To evaluate the efficacy, predictability, and safety of combined corneal collagen cross-linking (CXL), intracorneal ring segment (ICRS) implantation, and superficial phototherapeutic keratectomy (PTK) in patients with keratoconus. Methods: Fifty-five eyes received ICRS implantation, followed by CXL and PTK combination treatment. Patients were followed up for 6 months. Primary outcomes included Logarithm of the Minimum Angle of Resolution (LogMAR) uncorrected distance VA (UDVA) and corrected distance VA (CDVA), sphere, cylinder, mean spherical equivalent, index of surface variance, index of vertical asymmetry, keratoconus index, central keratoconus index, index of height asymmetry, and index of height decentration. Secondary outcomes were higher-order aberrations (HOAs), including HOA total, coma, spherical, secondary astigmatism, and trefoil. Results: At 6 months, there was a statistically significant improvement in UDVA, CDVA, sphere, and cylinder compared with baseline (P < 0.001). UDVA improved in 14% of the eyes to 20/25 and 96% had at least 20/40 or better spectacle corrected vision; 30.9% of the eyes were within ±0.5 diopter (D), 45.5% of the eyes were within ±1.0 D, and 74.5% of the eyes were within ±2.0 D. For CDVA, 1 eye (2%) lost 3 lines (but gained UDVA), 11% lost 1 line, 38% showed no change, and 49% gained between 1 and 8 lines of vision. Eighty-eight United Arab Emiratespercent of the eyes had at least 1 line of UDVA visual improvement, 79% improved by ≥2 lines, and 69% improved by ≥3 lines. HOA total, coma, spherical aberration, and secondary astigmatism showed improvements of −0.87 (P < 0.001), −0.84 (P < 0.001), −0.10 (P = 0.002), and −0.15 (P = 0.035), respectively. Conclusions: A combined procedure of ICRS implantation, CXL, and PTK is effective, predictable, and apparently safe for patients diagnosed with moderate keratoconus.
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