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Biomedical subjects

W J Benjamin

Publications and source records attributed to W J Benjamin.

29 records · Page 2Linked to original sources
PubMed1989

Clinical findings correlated with contact angles on rigid gas permeable contact lens surfaces in vivo.

Functional wettability of daily wear rigid gas permeable (RGP) contact lenses worn by 16 human subjects was monitored over a 4-month period during which wettability was also assessed with an equilibrium sessile-drop contact angle method in vivo. In all, 2,128 lens surface break-up time (LBUT) and in vivo contact angle data points were accumulated. Six hundred thirty-one associated graded evaluations of lens surface deposition and patient discomfort were also recorded. The four factors (LBUT, contact angle, deposition, and discomfort) were found to be correlated to each other, their paired values having statistically significant correlation coefficients. Contact angles were of predictive value for extremes of functional wettability, based on criterion of 20 degrees equivalent to an LBUT of 5 seconds. We confirm that surface deposition and subject discomfort are related to RGP lens wettability on the eye. In addition, the in vivo contact angle is perhaps the first contact angle measurement to be correlated with functional RGP wettability.

Contact Lenses↗
PubMed1988

Human cornea: superior and central oxygen demands.

Corneal oxygen demands, expressed as ratios of uptake rate relative to baseline rates derived from unstressed corneas, were determined with a micropolarographic system for central (closed eye) and superior (open eye) locations of one cornea of each of seven human subjects. The closed-eye central corneal measurements were repeated during two additional experimental sessions. Intrasubject variability of the three mean closed-eye central corneal rate ratios ranged as high as 23%, possibly representing effects of homeostatic mechanisms on the palpebral conjunctival capillaries of some subjects. For the open-eye superior cornea, which was covered by the upper eyelid of every subject prior to measurement, oxygen demand was found to have a greater intersubject range, but was diminished in magnitude relative to the demand associated with the closed-eye central cornea. Superior corneal oxygen demand was not found to be predictable from closed-eye central corneal oxygen demand or extent of eyelid overlap onto the cornea and thus indicated localized open-eye superior corneal environments that were significantly different from those of the corresponding closed-eye central corneas. Such localized environments may be critically important when gauging the susceptibility of particular eyes to superior corneal pathology during contact lens wear.

Adult↗
PubMed1988

Human cornea: individual responses to hypoxic environments.

Using a micropolarographic system, the responses of seven human corneas to oxygen atmospheres ranging from 20.9% to 0% were measured. Under normal atmospheric conditions, ratios of oxygen demand were observed between corneas as great as 1.23:1. Following 0% oxygen conditions, however, these ratios rose to a maximum of 1.93:1, i.e., representing demand differences between particular corneas of nearly 2:1. Such differences may prove increasingly important in the gauging of patient suitability and safety in relation to hypoxic stress, e.g., the extended wear of contact lenses.

Adult↗
PubMed1988

Oxygen consumption of the superior cornea following eyelid closure.

Oxygen depletion curves were recorded from the superior and central cornea with a micropolarographic system immediately following eyelid closure in 10 adult human subjects. Superior corneal oxygen uptake rates for the closed-eye state ranged from 13% below to 58% above, with a mean 15% greater than equivalent central corneal oxygen uptake rates. Chronic superior corneal hypoxia induced by upper eyelid coverage when the eyes are open is therefore accompanied by a deeper hypoxia relative to the central cornea of some individuals when their eyes are closed. This hypoxia adds to the physiological compromise endured by the superior cornea and is especially emphasized when contact lenses are worn.

Adult↗
PubMed1986

Human corneal oxygen demand: the closed-eye interval.

A micropolarographic system was used to measure the flux of oxygen crossing the tear epithelial interface of the human cornea just following lid-closure periods of 0-15 min, and just following a series of brief lid openings (0.2-0.3 s) of frequencies from 0 to 30 times/min. In all, 462 measurements spanning those two formats were made on the corneas of seven young healthy subjects. In the extended-closure format the average rate increased over the first 5 min, then stabilized at 2.51 times the oxygen-uptake rate under normal open-eye conditions. In the brief lid-opening format, frequencies of 30 openings/min reduced the oxygen uptake rate to 70% of that of the stabilized closed eye. Individual differences noted among subjects may influence their relative success in extended contact lens wear, and natural lid and eye movements during sleep may have at least transient effects on corneal oxygen supply and demand during those periods.

Adult↗
PubMed1986

Tear osmotic differences across the ocular surface.

We used a freezing point depression method to determine the osmolalities of 502 non-stimulated 200-nanoliter tear samples. The samples were collected hourly at 9 times on each of 6 days. Four reference (tear prism) sites on the ocular surface were used: mid-superior, mid-inferior, and the tear prisms at the medial and lateral canthi. While 256 of the samples were from a young (25 year old) male volunteer having no complaints of dry eyes, the remaining 246 samples were taken from a second male volunteer of the same age range, but who had occasional complaints of dry eyes. The mean osmolalities for all sites and all times for both subjects were found to be 315 and 331 mOsm/kg, respectively, and were significantly different (P = 0.0004). Two of the six time-averaged intersite comparisons investigated here were found to be significantly different for each of the subjects, with the inferior tear prism and the medial canthus being the only shared pairs present. The magnitudes and patterns of these osmotic site differences were found to shift for both subjects over time, although this was more prominent and with a greater hypertonic bias for the subject with dry eye complaints. While these data do demonstrate statistically different osmolalities across the ocular surfaces of the two subjects examined in this report, these findings must be considered a preliminary view of broader population patterns yet to be studied.

Eye↗
PubMed1986

Closed-lid factors influencing human corneal oxygen demand.

A micropolarographic system was used to measure the flux of oxygen crossing the tear-epithelial interface of the human cornea just following stabilization of four lid closure conditions. In all, 215 oxygen flux measurements were made on the corneas of 6 young healthy subjects, including 2 reference conditions: the normal open eye and anterior surface oxygen deprivation. When compared with the temperatures associated with certain of those conditions, oxygen demands greater than those predicted by a previous Q10 measurement were found. Proportional contributions of the non-temperature factor are presented, and the nature of its components suggested.

Adult↗
PubMed1985

Human cornea: oxygen uptake immediately following graded deprivation.

A micropolarographic system was used to measure the flux of oxygen crossing the tear epithelial interface of the human cornea just following stabilized exposure to eight oxygen atmospheres ranging from 0% to 20.9%. In all, 336 measurements were made on the corneas of seven young healthy subjects. The rate coefficients of their immediate postexposure oxygen uptakes were found to increase nearly linearly over the atmospheric range of 20.9% (air) down to about 1.5%. Below that level, however, a marked increase in the immediate recovery rate coefficient occurred, suggesting that at least two oxygen demand phases can be distinguished for the aerobically dependent pathways of the cornea.

Adult↗
PubMed1983

Human tears: osmotic characteristics.

Using a freezing point depression method, requiring volumes of only 200 nanoliters, the osmolalities of 324 tear samples collected at consecutive 10-minute intervals throughout 8.5-hour periods from each of six healthy young adults were measured. The population mean was found to be 318 mOsm/kg, with a population median of 315 mOsm/kg. Individual subject means ranged from 310 to 334 mOsm/kg. Short-term oscillations were observed for all subjects, with a net positive rate toward hypertonicity for the population of 1.43 mOsm/kg X hr-1 as the day progressed. Two subjects did demonstrate mild net rates of decrease, however. All eyes in the study were asymptomatic, suggesting a broader range of tear osmotic pressure among normals than previously suspected.

Adult↗
PubMed1983

Nanoliter tracking of the tears.

Microliter sampling opened the way in the 1970's for at least limited quantitative studies of the tear fluid. Now, nanoliter sampling offers a much less imposing technique for viewing even more subtle changes within the eye's most immediate environment. Examples, based on nanoliter sampling, are given of certain transient effects that even a soft lens can induce during the earliest periods of wear.

Contact Lenses, Hydrophilic↗