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Biomedical subjects

S D Klyce

Publications and source records attributed to S D Klyce.

At least 109 records · Page 6Linked to original sources
PubMed1972

Electrical profiles in the corneal epithelium.

1. The potentials and resistances associated with the cell membranes of the rabbit corneal epithelium were studied with 3 M-KCl-filled micro-electrodes.2. In the isolated cornea, the transepithelial potential was identical in polarity and magnitude to the simultaneously measured total corneal potential. In contrast to previous findings, the stromal potential was positive to the tear side. Negative stromal potentials apparently derive from inadequate electrodes or method of penetration, and were not found to be a function of filling solution. Transepithelial potential was also identical to over-all corneal potential in the living rabbit eye.3. In the isolated preparation, the average potential profile occurred in three distinct steps across the epithelium. By means of iontophoretic dye injection it was shown that these steps occurred across the outer membrane of the squamous cell, the transition region between the wing and basal cell, and across the inner membrane of the basal cell.4. The transverse membrane resistance of the outer epithelial membrane accounted for 60% of total corneal resistance. As a result, short-circuit current, which depolarizes the cornea, led to a hyperpolarization of the outer membrane, while affecting deeper membrane potentials little or not at all.5. The spontaneous potential of the outer membrane varied inversely with corneal potential in both normal and chloride-free Ringer, while the potential of the inner membrane of the basal cell was relatively constant, approaching the theoretical Nernst potential for potassium. The potential of the outer membrane was at chloride equilibrium and was sensitive to extracellular shunts. A Thevenin equivalent drawn for the epithelium suggested that half of the outer membrane potential could be attributed to loop currents. The potential step between wing and basal cells could be accounted for in terms of loop currents driven by the corneal potential through the epithelium.6. The potential profile of the frog corneal epithelium was similar to that of the rabbit. However, the major resistance in the frog cornea was associated with the basal cell membrane rather than with the squamous cell outer membrane. Quasi-instantaneous rectification was found for both epithelia. In the rabbit chloride rectified inwardly.

Animals↗
PubMedDate not supplied

Advances in the analysis of corneal topography.

Recent advances in topographic analysis have provided powerful tools for detecting subtle, but clinically significant, alterations of corneal contour. This article compares keratometry, keratoscopy, and computer-assisted topographic analysis and provides specific examples of the sensitivity of computer-assisted systems in revealing topographic alterations that were not previously discernable. Quantitative descriptors of corneal topography such as the surface asymmetry index, the surface regularity index, and simulated keratometry value augment the information provided by color-coded topographic maps.

Contact Lenses↗
PubMedDate not supplied

Videokeratography for quantitative surface analysis of used soft contact lenses.

The greater utilization of soft contact lenses calls for the development of new and objective methods of evaluating the optical performance of the different lens types, in situ. We used videokeratography to examine the surface topography of soft contact lenses that had been worn for more than 1 year on 27 eyes of 23 patients, and compared the resulting color-coded maps and topographic indices as well as contact lens-corrected visual acuities, with those obtained with new replacement lenses on the same eyes. Visual inspection of the color-coded maps revealed differences in the surface characteristics of the used and new lenses. Comparison of quantitative indices including the SAI (Surface Asymmetry Index), IAI (Irregular Astigmatism Index), SRI (Surface Regularity Index), and SDP (Standard Deviation of Powers) showed that asymmetry, surface irregularity, potential visual acuity (derived from the SRI), and corneal power distribution were significantly poorer with the used lenses than with the new (P = 0.0001). The videokeratoscope is useful for evaluating the soft contact lens surface in situ, as an indicator of optical quality; it also permits the objective evaluation of lens cleaning techniques.

Adolescent↗
PubMedDate not supplied

Detection and classification of mild irregular astigmatism in patients with good visual acuity.

Videokeratography has been available for a decade, and this test is essential for determining the presence and type of irregular corneal astigmatism. Three eyes diagnosed with myopic astigmatism and considered good candidates for refractive surgery with conventional examination were studied. Color-coded maps with videokeratography showed regular astigmatism in one eye and the existence of irregular astigmatism in two eyes. Videokeratography showed that one of these eyes had a keratoconus suspect pattern and the second showed a pattern consistent with pellucid marginal degeneration. Videokeratography can detect and classify irregular astigmatism in cases where routine examination shows no abnormal findings.

Adolescent↗
PubMedDate not supplied

Epikeratophakia: the surgical correction of myopia. I. Lathing of corneal tissue.

In order to develop a surgical technique as an alternate method for the treatment of myopia, we have adapted the epikeratophakia corneal graft procedure. The procedure is not burdened with some of the side effects associated with radial keratotomy and a wide range of predictable correction can be obtained. Preliminary trails in a non-human primate model have indicated that myopia up to -27 diopters can be corrected accurately with these grafts. In this paper we present the mathematical model for the lathing of epikeratophakia grafts for the correlation of myopia, and preliminary results in the non-human primate model.

Animals↗
PubMedDate not supplied

Analysis of the effects of astigmatism and misalignment on corneal surface reconstruction from photokeratoscopic data.

This article presents a general method of error analysis for reconstruction algorithms employed by corneal topography systems and applies this method to assess the accuracy of the Wang reconstruction algorithms. Using mathematical surface reconstructions, the method detects artifacts introduced in topographic analysis by astigmatism and misalignment. For the Wang algorithms, error introduced by astigmatism was less than 1% of the true value for surfaces with more than 10.00 diopters of astigmatism. A 1-mm translational misalignment of the analyzed surface introduced error of no more than 1.3%. Errors caused by rotational misalignment were less than 3% for misalignments of 5 degrees or less. It is concluded from the error analysis method that the Wang algorithms are sufficiently accurate for use in the analysis of corneal topography. Similar analyses need to be accomplished for the validation of commercially available corneal topography systems.

Algorithms↗
PubMedDate not supplied

Terrien's marginal degeneration: corneal topography.

Computer-assisted corneal topographic analysis was used to evaluate the corneal contour of four patients with Terrien's marginal degeneration. The corneal topography in these patients was characterized by flattening over the areas of peripheral thinning produced by the disorder. When thinning was restricted to the superior and/or inferior areas of the peripheral cornea, there was a relative steepening of the corneal surface approximately 90 degrees away from the midpoint of the thinned area. This resulted in high against-the-rule or oblique astigmatism characteristic of the disorder. This common pattern is attributable to the frequency with which the superior and/or inferior peripheral cornea is preferentially involved in Terrien's marginal degeneration. In some patients, the central corneal topography may remain relatively spherical if the area of thinning is small or if the disorder extends around the entire circumference of the cornea.

Adult↗
PubMedDate not supplied

Topographic changes that occur with 10-0 running suture removal following penetrating keratoplasty.

Twelve eyes undergoing penetrating keratoplasty with a double-running suture technique had corneal topographical analysis immediately before and one month after 10-0 suture removal. Substantial changes in astigmatism were evident following suture removal. Twenty five percent of eyes showed a decrease of 1 D, 33% of eyes showed a decrease of 3 D, 8.3% of eyes showed an increase of 1 D, 8.3% of eyes showed an increase of 2 D, 16.6% of eyes showed an increase of 3 D, and 8.3% of eyes showed an increase of 4 D of astigmatism following suture removal. The mean corneal astigmatism did not show a significant change from a mean of 5.3 D after suture removal. There was less individual variation of spherical corneal power following suture removal. Thirty three percent of eyes showed a decrease of 1 D, 33% of eyes showed a decrease of 2 D, 8.3% of eyes showed a decrease of 3 D, 18.3% of eyes showed an increase of 1 D, and 6.6% of eyes showed an increase of 2 D of spherical power following suture removal. The surface asymmetry index (SAI), a centrally weighted measure of corneal surface irregularity, decreased significantly (P less than 0.04) from a mean of 1.17 before suture removal to a mean of 0.93 after suture removal. These results suggest that surface irregularity may be decreased following the removal of a single running 10-0 nylon suture following penetrating keratoplasty.

Astigmatism↗
PubMedDate not supplied

The corneal topography of epikeratophakia.

Epikeratophakia is a surgical technique initially developed for the correction of aphakia, and later adapted for the correction of keratoconus and myopia. The concurrent development of color-coded computerized corneal topography has greatly assisted in the evolution of epikeratophakia. Corneal topography has demonstrated the importance of both accurate centration of the epikeratophakia lenticle over the visual axis and the size of the optical zone on the final refractive results. Corneal topographic changes associated with correction of aphakia are primarily the result of steepening of the anterior radius of curvature of the cornea, in contrast to myopic correction which results in flattening of the anterior cornea. Correction of keratoconus results from a physical compression of the cone thereby flattening both the anterior and posterior radii of curvature. Preoperative topography in patients with keratoconus permits the precise position and extent of both regular and irregular astigmatism mation may assist in designing the optimal lenticle size and amount of graft decentration necessary to achieve the maximal surgical effect. Corneal topographic mapping has also been helpful in the management of postoperative astigmatism following epikeratophakia. Topography identifies the location and extent of both regular and irregular astigmatism which assists in planning of both surgical and nonsurgical intervention. Corneal topographic mapping has also been extremely helpful in the management of postoperative astigmatism following epikeratophakia. Topography identifies the location and extent of both regular and irregular astigmatism which assists in planning of both surgical and nonsurgical intervention.

Adult↗
PubMedDate not supplied

Rigid contact lens decentration: a risk factor for corneal warpage.

Clinically significant contact lens induced corneal warpage is seen in a small proportion of soft and rigid contact lens wearers. Previous studies using the keratometer have found no correlation between the fit of the lens and the induced topographic changes. In this study, using computer-assisted topographic analysis, seven eyes (four patients) with rigid contact lens-induced corneal warpage were noted to have topographic abnormalities that correlated with the decentered resting position of the contact lens on the cornea. The warpage topography for each of these corneas was characterized by a relative flattening of the cornea underlying the resting position of the contact lens. Lenses that rode high, for example, produced flattening superiorly and resulted in a relatively steeper contour inferiorly that simulated the topography of early keratoconus patients who had not worn contact lenses. After discontinuing contact lenses the corneal topography returned to a normal pattern in five eyes. Two eyes retained asymmetry that is not characteristic of normal corneas. Up to 6 months was required for the corneas to return to a stable topography after contact lens wear was discontinued.

Adult↗
PubMedDate not supplied

Methods of analysis of corneal topography.

The visual inspection of photokeratoscope mires permits the diagnosis of advanced anomalies in corneal shape and is an extremely useful adjunct to keratometry and slit-lamp microscope examination. However, corneal distortions too small to be appreciated by visual inspection of keratographs can seriously degrade visual acuity. In this article, an outline of the problems involved and the steps necessary to accomplish modern quantitative corneal topography is given.

Cornea↗