Biomedical subjects

B A Fink

Publications and source records attributed to B A Fink.

25 records · Page 2Linked to original sources

PubMed1991

Effects of rigid contact lens edge lift changes on tear pump efficiency.

The effects of rigid contact lens axial edge lift changes on corneal oxygenation and tear exchange with the blink were studied for lenses of five axial edge lifts (0.05 to 0.13 mm in 0.02-mm steps). The overall and optic zone diameters were maintained at 8.8 and 7.4 mm, respectively, and all other parameters were held constant. Oxygen uptake rates were measured for the normal open eye after 5 min of static (without blinking) and dynamic (with blinking once every 5 s) contact lens wear. As expected, no significant differences were found in the oxygen uptake rates associated with the static wear of the contact lenses; however, under dynamic conditions, increasing edge lift was associated with a reduction in oxygen demand. The differences between data obtained under static and dynamic conditions increased with increasing axial edge lift, and subjects with small palpebral aperture sizes seemed to benefit more from increasing axial edge lift.

Adult↗

PubMed1990

Biochemical changes in the developing rat central nervous system due to hyperthermia.

Rat embryos at 10 days of gestation were exposed to 43 degrees C for 8 minutes by submerging the exteriorized right uterine horn in heated saline solution and then reinserting the uterine horn into the abdominal cavity. At 15 days, the fetuses were removed, and cells from the cerebral hemispheres were dissociated and grown as primary cultures. Embryos from the left uterine horn served as controls. No morphological changes were observed between the cultures of cells from control and heat-exposed embryos at different days in culture. However, exposure of embryos to hyperthermia at 10 days significantly affected the developmental pattern of activities of acetylcholine esterase associated with cholinergic neurons and of 2',3'-cyclic nucleotide phosphohydrolase associated with oligodendrocytes and myelin membrane formation. These results suggest that hyperthermia at 10 days of gestation in the rat may lead to an impairment in the development of neurons and oligodendrocytes in the central nervous system.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

PubMed1990

Influence of palpebral aperture height on tear pump efficiency.

Oxygen uptake rates were measured on 6 human corneas fitted with a standardized rigid contact lens in order to determine the relation between vertical palpebral aperture height and exchange efficiency of tears in such systems. The contribution provided by tear exchange to the oxygen available to the cornea was isolated through the use of lenses of negligible transmissivity (PMMA). Measurements of corneal oxygen uptake were made on the normal open eye, after 5 min of static (with no blinking) open eye contact lens wear, and after 5 min of dynamic (with blinking every 5 s) contact lens wear. The difference between the oxygen demand associated with static conditions (SC's) and that associated with dynamic conditions (DC's) is an index of the tear pump efficiency for each subject. A statistically significant correlation (p less than 0.0001) was found between the vertical palpebral aperture height and the tear bulk-flow of oxygen to the cornea, confirming that small palpebral apertures can restrict lens motion.

Adult↗

PubMed1990

Influence of rigid contact lens overall and optic zone diameters on tear pump efficiency.

To determine the effects of contact lens overall diameter on tear pump efficiency, oxygen uptake rates were measured for the open-eye condition and following steady-state periods of static (without blinking) and dynamic (with blinking once every 5 s) contact lens wear of oxygen-impermeable (polymethylmethacrylate) lenses of 5 overall diameters (8.2, 8.5, 8.8, 9.1, and 9.4 mm). The optic zone diameters were 1.4 mm smaller than the overall diameters in each case, while all other parameters remained constant. Differences in corneal oxygen demand following the static and dynamic conditions are a quantitative index of the tear pump efficiency for each lens size on the same cornea, and the differences were found to increase with reduction in lens overall diameter. This indicated that a more efficient tear pump was associated with small diameter designs. In addition, subjects with large palpebral aperture size, relative to lens overall diameter, were found to demonstrate better tear exchange.

Adult↗

PubMed1990

Corneal oxygenation: blink frequency as a variable in rigid contact lens wear.

Using a micropolarographic system, we measured the responses of six human corneas to nine oxygen exposure conditions: to air (continuous open-eye) with no contact lens in place, and to eight interblink intervals (1, 2, 3, 4, 5, 6, 7, and 300 s durations) with an oxygen impermeable lens in place. The corneal oxygen uptake rates immediately following each of those conditions were direct indices of tear bulk-flow exchange under a rigid contact lens as an oxygen route. Greatest efficiencies in reducing corneal oxygen demand were associated with the two highest blink frequencies examined (namely, for interblink intervals of 2 s or less). Even at those frequencies oxygen demands ranging from 4 to 6 times the open-eye, non-wearing, baseline rate for each eye typically occurred, clearly justifying the need for a supplementary oxygenation route, for example, directly through rigid contact lens materials having inherently high oxygen permeabilities.

Adult↗

PubMed1982

A comparison of three methods of measurement of toric soft lens orientation.

A group of five subjects were fitted with truncated toric soft lenses varying in minus cylinder power from 1 to 4 D in 1 D steps at axes of 90 and 180. After 15 min of lens wear, the location of the lens was measured by three techniques: the projected slitlamp photographic technique, measurement with a protractor graticule in the slitlamp eyepiece, and alignment of the slitlamp beam with markings on the lens. Analysis of the data by a four-level analysis of variance and a t-test showed no significant difference between the three methods of measuring the toric soft lens orientation.

Contact Lenses, Hydrophilic↗

PubMedDate not supplied

Poland's syndrome in one identical twin.

Female twins were evaluated at the Shriners Hospital in Lexington, Kentucky. One twin was normal, and the other twin had the classic findings of Poland's syndrome, manifested by absence of the pectoralis major and symbrachydactyly of the right upper extremity. Buccal smears from each child were submitted for DNA testing. The test confirmed monozygosity with 99.9% probability. Some previous reports have stated that Poland's syndrome is an autosomal dominant, genetically determined trait, whereas others have maintained that there is no genetic association. The original case described by Poland in 1841 was his cadaver, and no family history was reported. This twin study provides strong evidence that the condition is not determined by gene transmission.

Diseases in Twins↗