Peer-reviewed Articles

Please use the archived list on the right to look at past peer-reviewed articles.

1993

Doughty,M. J., Fonn,D. Pleomorphism and endothelial cell size in normal and polymegethous human corneal endothelium. International Contact Lens Clinic 1993;20,5-6:116-123. [ Show Abstract ]

The normal human corneal endothelium is composed of a tessellated mosaic of cells with different numbers of sides. A number of published studies indicate that while six-sided cells predominate (58-74%), significant numbers of five-sided (13-22%) and seven-sided (11-18%) are present along with occasional four-, eight-, nine- and even 10-sided cells. In polymegethous endothelia (associated with polymethyl methacrylate [PMMA] lenses and extended wear soft contact lenses [EW SCL]), the decline in the percentage of six-sided cells is associated with increases in the percentage of four-, five-, seven-, or eight-sided cells. Our analysis of photo slit-lamp micrographs revealed that the four- or five-sided cells tend to be smaller than the six-sided cells, whereas the seven-sided or larger cells are larger than six-sided cells. As a result, analyses of the average areas of each cell type indicate that the greater the pleomorphism (associated with polymegethism) the steeper the slope of a plot relating cell areas to the number of cell sides. The relationship is not necessarily linear (as suggested in previous reports), but does indicate that the remodeling of the endothelium (when significant cell loss is not evident) may follow some formal ordered process. © 1993.

Doughty,M. J., Fonn,D., Nguyen,K. T. Assessment of the reliability of calculations of the coefficient of variation for normal and polymegethous human corneal endothelium. Optometry and Vision Science 1993;70,9:759-770. [ Show Abstract ]

In endothelial morphometry, uncertainty exists concerning how many cells should be measured. A study was undertaken to calculate mean cell area and coefficient of variation (COV) of cell areas using different numbers of cells from photo-slitlamp pictures and published micrographs. Groups of 65, 95, or 165 tesselated cells were measured and area and COV values calculated in progressive sets of 5 cells; each pair of values was compared to that obtained using all cells in each group. The results show that, for both normal (homomegethous) and irregular (polymegethous) endothelia, even cell counts as low as 50 cells can usually provide average cell area values that are within 1 to 2% of the values estimated from larger groups of cells. A similar reliability was observed for estimates of COV for normal endothelia. However, for polymegethous endothelia, even with 100 cells analyzed, the estimates of COV generally only approached a +/- 4% reliability. This uncertainty in COV estimates should be considered in both comparative studies and in regression analyses of COV changes over time or other variables.

Elliott,D. B., Fonn,D., Flanagan,J., Doughty,M. Relative sensitivity of clinical tests to hydrophilic lens-induced corneal thickness changes. Optometry and Vision Science 1993;70,12:1044-1048. [ Show Abstract ]

The relative sensitivity of the van den Berg Straylightmeter, slitlamp biomicroscopy, a modified optical pachometer, Bailey-Lovie logMAR visual acuity (VA), and two glare tests (The Brightness Acuity Tester used with 10% contrast VA and Pelli-Robson contrast sensitivity) to hydrophilic contact lens-induced edema was assessed in 19 subjects (mean age 25.9 +/- 4.5 years). After baseline assessments, subjects wore thick hydrogel lenses on one eye which was patched tightly for 3 h. Assessments were repeated at frequent intervals after lens removal to assess recovery. None of the pachometer measurements returned to baseline within the 2-h monitoring period, although the majority were within 2% of baseline corneal thickness. The average time for the Straylightmeter scores to recover to baseline values after the lens removal was 90 min, which was similar to the time when visible edema at the slitlamp disappeared. The average time for return to baseline of logMAR VA and the two glare tests was consistently two to three times shorter than the time for the Straylightmeter score. The Straylightmeter therefore provided assessments of corneal edema similar to slitlamp examination and was more sensitive than VA or glare testing.

Elliott,D. B., Yang,K. C. H., Dumbleton,K., Cullen,A. P. Ultraviolet-induced lenticular fluorescence: Intraocular straylight affecting visual function. Vision research 1993;33,13:1827-1833. [ Show Abstract ]

Ultraviolet radiation (UVR) excitation of fluorophores within the crystalline lens results in intraocular straylight. These fluorescent emissions are known to increase with age. The visual effect of this increase in fluorescent straylight has not previously been published. In this study, the visual deficit associated with UV-induced lenticular fluorescence was measured for 61 normal subjects between the ages of 21 and 80 yr of age using the Regan visual acuity charts at varying levels of contrast. UVR was shown to decrease low contrast acuity and this loss increased linearly with age.

Simpson,T. L. Effect of asymmetry on calculations of convergence in prism diopters. Optometry and Vision Science 1993;70,3:201-204. [ Show Abstract ]

Calculations of convergence in units of prism diopters are based on an assumption that convergence is symmetrical, that is, the visual axes intersect on the median plane. The effect of departure from symmetrical convergence is shown to produce systematic errors in calculations of convergence distance, if the convergence angle is constrained to be constant. On the other hand, if the convergence distance is constrained to be constant, departure from symmetry results in a systematic reduction in the convergence angle. Because these errors are disregarded in the specification of convergence in prism diopters, care should be taken in using these units for larger amounts of asymmetrical convergence.