PubMed · 12409922
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Robert L Schultze. 2002. Microkeratome update.. https://doi.org/10.1097/00004397-200210000-00007
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Tissue-on-tissue friction testing was used to determine how instillation of hydrophilic polymer-containing formulations between the "blinking" tissues would compare with lubrication by saline, alone, or an oil-emulsion preparation. Best results were obtained for a formulation that contained active demulcents polyethylene glycol (PEG 400) and propylene glycol (PG), as well as a gellable polymer hydroxypropyl guar (HP-Guar) in a borate-buffered solution, in comparison with hydroxypropylcellulose-containing and carboxymethylcellulose-containing formulations. Superior performance of all the formulations was found for lubricating tissue-on-tissue couples, compared with metal-oxide-to-metal oxide interfaces, or metal oxide-to-tissue interfaces. A reciprocating pin-on-disc type friction/wear test device articulated the intimal faces of preserved human umbilical cord vein segments under increasing loads during simulated continuous "eye-blinking" with addition of increasing weights up to 60 g/cm2, simulating maximal eyelid force on the orbital globe. The tissue-on-tissue couples moved from liquid phase lubrication to boundary lubrication. After residual formulations were rinsed away with saline, persistence of low friction at the highest loads was indicative of formulation substantivity. Human umbilical cord vein segments were utilized in saline-wetted tissue-on-tissue couples that showed variable starting coefficients of friction in the range 0.2-0.4, producing moderate tearing and disruption of the interfacial layers above the medial collagen zone. The best-performing formulations instilled to the tissues pre-wetted with saline apparently reacted separately with each tissue face to produce a lower final and persistent coefficient of friction of about 0.05. Scanning electron microscopy and light microscopy of these guar-modified tissue specimens showed only a few superficial tissue disruptions, and some interphase swelling consistent with polymer uptake. The frictional values for lubricated couples having non-tissue members were considerably higher than the coefficients of friction measured for the similarly lubricated tissue-on-tissue couples, emphasizing the requirement that appropriate simulations are critical to obtaining clinically predictive data.
OBJECTIVE: To test the validity and generalizability of the Ocular Hypertension Treatment Study (OHTS) prediction model for the development of primary open-angle glaucoma (POAG) in a large independent sample of untreated ocular hypertensive individuals and to develop a quantitative calculator to estimate the 5-year risk that an individual with ocular hypertension will develop POAG. DESIGN: A prediction model was developed from the observation group of the OHTS and then tested on the placebo group of the European Glaucoma Prevention Study (EGPS) using a z statistic to compare hazard ratios, a c statistic for discrimination, and a calibration chi2 for systematic overestimation/underestimation of predicted risk. The 2 study samples were pooled to increase precision and generalizability of a 5-year predictive model for developing POAG. PARTICIPANTS: The OHTS observation group (n = 819; 6.6 years' median follow-up) and EGPS placebo group (n = 500; 4.8 years' median follow-up). TESTING: Data were collected on demographic characteristics, medical history, ocular examination visual fields (VFs), and optic disc photographs. MAIN OUTCOME MEASURE: Development of reproducible VF abnormality or optic disc progression as determined by masked readers and attributed to POAG by a masked end point committee. RESULTS: The same predictors for the development of POAG were identified independently in both the OHTS observation group and the EGPS placebo group-baseline age, intraocular pressure, central corneal thickness, vertical cup-to-disc ratio, and Humphrey VF pattern standard deviation. The pooled multivariate model for the development of POAG had good discrimination (c statistic, 0.74) and accurate estimation of POAG risk (calibration chi2, 7.05). CONCLUSIONS: The OHTS prediction model was validated in the EGPS placebo group. A calculator to estimate the 5-year risk of developing POAG, based on the pooled OHTS-EGPS predictive model, has high precision and will be useful for clinicians and patients in deciding the frequency of tests and examinations during follow-up and advisability of initiating preventive treatment.
Factors that influence the polarographic measurement of the oxygen uptake of the cornea are reviewed. These factors include the technique, electrode assembly, oxygen reservoir, membrane material and thickness, oxygen tension of the corneal environment, duration of exposure to environmental conditions and time to application of the probe all influencing measured oxygen uptake rates. Subject factors include lid position, palpebral aperture size, blinking, corneal thickness, and corneal integrity. Contact lens wear influences corneal oxygen uptake, with lens material and design parameters influencing rates obtained both under static (without blinking) and dynamic (with blinking) conditions. Measurement of corneal oxygen uptake rates remains an excellent method to quantify the oxygen supply in contact lens systems that include the contact lens, the tears, and the cornea, in which oxygen flux is influenced by the thickness and diffusion characteristics of each component.