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Biomedical subjects

S D Klyce

Publications and source records attributed to S D Klyce.

At least 55 records · Page 3Linked to original sources
PubMed1992

Physiological effects of tert-butyl hydroperoxide on the rabbit corneal epithelium.

Rabbit corneas were mounted atraumatically into an automatic voltage clamp apparatus for the determination of open circuit potential difference and short circuit current. The corneal tissue was bathed on both sides with a Ringer solution, continuously stirred and aerated. After a minimum 1 hour equilibration, a single dose of tert-butyl hydroperoxide (t-BHP) (0.1 mM to 2 mM) was administered to the tear-side solution. This led to an immediate fall in epithelial potential difference and short circuit current. The electrical conductance tended to be subnormal during the peak response. The initial decreases were partially reversed, but even after several hours the majority of corneas sustained abnormal levels of potential difference and conductance. Administration of 2 mM t-BHP to the tearside solution led to an immediate fall in epithelial thickness to -25% of baseline. This was followed by large-amplitude oscillations in corneal epithelial thickness which were sustained over several hours. We conclude that prolonged exposure of the perfused rabbit cornea to small tearside amounts of t-BHP are capable of modulating the electrophysiologic integrity of the corneal epithelium. T-BHP exceeding 1 mM in the tears could compromise the non-catalase dependent antioxidant defense mechanisms in rabbit corneal epithelium.

Animals↗
PubMed1991

Quantitative descriptors of corneal topography. A clinical study.

Quantitative descriptors of corneal topography determined by computerized algorithm and designed to augment the information derived from topographic maps were evaluated in a clinical study. The surface regularity index, a measure of central corneal optical quality, was highly correlated with best spectacle-corrected visual acuity (rho = 0.80, P less than .001). The relatively low correlation between the surface asymmetry index, a measure of central corneal asymmetry, and best spectacle-corrected visual acuity (rho = 0.62, P less than .005) suggests that corneal symmetry is a lesser but still important determinant of the optical performance of the anterior corneal surface. There was also a high correlation between factors determined from computer-generated orthogonal simulated keratometer values and clinical keratometry values (mean corneal power, total corneal cylinder, and the location of the steepest corneal meridian). The information derived from these algorithms has both clinical and research applications and can be incorporated into computer-assisted topographic analysis systems.

Algorithms↗
PubMed1991

Changes in corneal topography after excimer laser photorefractive keratectomy for myopia.

Computer-assisted analysis of corneal topography was performed in 17 normally sighted human eyes during the first year after excimer laser photorefractive keratectomy (PRK) for myopia. Laser ablation of the central cornea produced an optical zone with a smooth power transition to the peripheral cornea. Decentration of the ablation was noted in some eyes (less than 0.5 mm in 3 eyes, 0.5 to 1.0 mm in 10 eyes, 1 to 1.5 mm in 3 eyes, and 2.1 mm in 1 eye), suggesting that careful alignment of the laser beam is critical. Improved methods to align the ablation within the center of the entrance pupil are needed. In 12 of 17 eyes, the topographic pattern appeared to stabilize between 3 and 7 months after PRK. In the remaining five eyes, central ablation power changed by more than 0.5 diopters (D) between the 6- and 12-month examinations. Regression was more common and more pronounced in eyes with intended corrections more than 5 D, whereas the majority of eyes with intended corrections of 5 D or less showed good correspondence between the final change in central ablation power and the attempted correction. Two eyes had a loss of at least two lines of best spectacle-corrected visual acuity that was attributable to irregular astigmatism, decentration of the ablation, and/or corneal opacification.

Adult↗
PubMed1991

Central photorefractive keratectomy for myopia. Partially sighted and normally sighted eyes.

Ten partially sighted and 19 normally sighted eyes underwent excimer laser photorefractive keratectomy for the correction of myopia. Nine of the partially sighted and 17 of the normally sighted eyes had 12 months of follow-up. Epithelial healing was complete in all eyes by day 6. None of the eyes had recurrent erosions, infections, or other medical complications. An increase in corneal haze after surgery was followed by a slow trend toward clearing. Average uncorrected visual acuity in the 7 normally sighted eyes with attempted corrections of 5 diopters (D) or less was 20/40 from month 2 on; the eyes with greater than 5 D attempted corrections had an average of 20/80--at month 2, which declined to 20/200--by month 6. Best spectacle-corrected visual acuity was within +/- 1 Snellen line of preoperative values in 14 of the normally sighted eyes, improved 2 or more lines in 2 eyes, and worsened two or more lines in two eyes. Hard contact lens overcorrection restored all of the two-line loss in 1 eye and 1 line of the 3-line loss in the other. Refraction and keratometry indicated corneal flattening without induced astigmatism.

Adult↗
PubMed1991

Corneal topography of keratoconus.

Sixty-three eyes of 49 patients with keratoconus were studied by means of computer-assisted corneal topographic analysis. Two patients with keratoconus in one eye had no topographic evidence of keratoconus in the opposite eye. Keratoconic topographic alterations were classified into two groups. The majority of the patients (72%) had peripheral cones, with steepening extending to the limbus. In this group, the steepening was commonly restricted to one or two quadrants. In some cases, however, the changes involved nearly the entire corneal surface. The remaining group (about one quarter of the keratoconus patients) had steepening that was restricted to the central cornea. In either group, the topographic alterations in the two eyes of any single patient were characterized by a high degree of nonsuperimposable mirror-image symmetry (enantiomorphism). In the majority of patients, however, there was a large and statistically significant disparity between the two eyes in the power at the apex of the cone and the total cylinder [mean differences 8.2 +/- 6.0 D (p less than 0.0001) and 4.3 +/- 2.7 D (p less than 0.0001), respectively].

Humans↗
PubMed1990

One-year refractive results of central photorefractive keratectomy for myopia in the nonhuman primate cornea.

Photorefractive keratectomy for the correction of myopia was performed in 32 eyes of 16 green monkeys. The corneas healed satisfactorily, with normal formation of basal lamina and hemidesmosomal attachments visible in 14-week histologic specimens. No recurrent erosions were observed clinically. After a transient period of faint haze, all corneas were clear at 17 weeks and remained clear through the 1-year follow-up. In terms of accuracy, all corneas demonstrated a significant flattening compared with preoperative values, but no significant difference was seen between the groups with different intended corrections (1.5 and 3 diopters). The changes in corneal shape stabilized by 17 weeks, as measured by keratometry. The clinical results suggest that mechanical removal of the epithelium is preferable to laser ablation of the epithelium. Overall, the results demonstrate that excimer laser ablation of the corneal stroma can produce a stable diptric change in the primate cornea with good healing and long-term corneal clarity.

Animals↗
PubMed1990

Central photorefractive keratectomy for myopia. The blind eye study.

Prior to undertaking a study in sighted human eyes, we performed photorefractive keratectomy with the 193-nm excimer laser for the correction of myopia in nine legally blind eyes to evaluate safety, efficacy, predictability, and stability. In most cases, reepithelialization was complete by 5 days after surgery; no recurrent erosions were seen. By the end of the 6-month study, all of the corneas had a 0 or 1+ clarity score, on a scale of 0 (clear) to 5+ (opaque). Keratometry and pachometry demonstrated stable flattening of the corneas. One month after surgery, changes in refraction evaluated by retinoscopy showed fair predictability, with no significant increase in refractive or keratometric astigmatism, followed by some regression of effect by the end of the study, possibly caused by anatomical remodeling. The amount of regression appeared to be directly related to the amount of correction intended, suggesting that this effect would not be clinically important in the treatment of mild to moderate myopia.

Adult↗
PubMed1990

Theoretical basis for an anomalous temperature coefficient in swelling pressure of rabbit corneal stroma.

In the rabbit corneal stroma, the swelling pressure, P, has been reported to have an anomalous (negative) temperature coefficient, alpha P, contradicting traditional Donnan swelling theory. A parallel-plate, diffuse double layer Gouy-Chapman model was used to resolve this discrepancy. The present model incorporates the possibility that surface charge, sigma, is temperature dependent. It is shown that negative, zero, or positive coefficients of swelling pressure change with temperature are not mutually exclusive conditions, but can be attributed to the same underlying mechanism. For likely values of alpha P(range -7 x 10(-3) K-1 to +3.2 x 10(-3)K-1), the effective stromal charge has a negative temperature dependency, or dln sigma/dT less than 0. The present formalism is robust against variation in assumed alpha P, and is able to simultaneously satisfy the known values of swelling pressure, its thermal dependency, and stromal charge. These results implicate significant coulombic forces behind P. Predicted stromal surface charge is approximately 0.01 Cm-2. The predictions were confirmed with macrocontinuum Donnan swelling theory, suggesting that Donnan osmotic swelling is the principal macroscopic component of P.

Animals↗
PubMed1990

An adjustable single running suture technique to reduce postkeratoplasty astigmatism. A preliminary report.

The authors compared postkeratoplasty astigmatism over a 4-month period after surgery in a randomized, prospective study of two groups of patients (total N = 18) who received two different suture techniques. The test group N = 8) had a single running suture with postoperative suture adjustment; on the basis of computer-assisted topographic analysis, the suture was tightened in the flatter meridian and loosened in the steeper meridian in the first month after surgery. The control group (N = 10) had a standard double running suture procedure with no postoperative adjustment; the single running 10-0 nylon suture was removed 3 months after surgery. Four months after penetrating keratoplasty, mean (+/- standard deviation) astigmatism in the test group was 1.7 +/- 0.7 diopters (D), and all patients had less than 2.6 D of astigmatism. In the control group, mean astigmatism was significantly higher (5.4 +/- 2.4 D; range, 0.7-9.0 D; P less than 0.01). The results suggest that postkeratoplasty astigmatism can be reduced with the single running suture technique accompanied by postoperative suture adjustment.

Astigmatism↗
PubMed1990

Topographic changes in contact lens-induced corneal warpage.

Twenty-one eyes of 12 patients with contact lens-induced corneal warpage were followed prospectively using computer-assisted topographic analysis. Sixteen eyes had worn rigid contact lenses (13 eyes, polymethylmethacrylate; three eyes, gas-permeable), and five eyes had worn soft contact lenses. Initial corneal topographic patterns were characterized by the presence of central irregular astigmatism, loss of radial symmetry, and frequent reversal of the normal topographic pattern of progressive flattening of corneal contour from the center to the periphery. A correlation was noted between the initial corneal topography and the resting position of the contact lens on the cornea for nine of the 16 eyes with rigid contact lenses. Initial topography for each of these corneas showed relative flattening of the corneal contour underlying the resting position of a decentered contact lens. Superior-riding lenses produced a topography that simulated early keratoconus. After cessation of contact lens wear, 16 of 21 eyes had a change in corneal shape to a topography that was consistent with a normal pattern. Five corneas stabilized with an abnormal topographic pattern. A much longer time without contact lenses than had been previously reported, up to 5 months, was required for a return of a stable corneal topography in eyes with contact lens-induced corneal warpage caused by rigid lenses.

Astigmatism↗
PubMed1989

Corneal compression sutures for the reduction of astigmatism after penetrating keratoplasty.

We placed interrupted 9-0 nylon sutures across the graft-host interface of ten eyes with more than 5 diopters of keratometric cylinder after penetrating keratoplasty in order to steepen the flattest corneal meridian and reduce the amount of corneal cylinder. Placement of compression sutures reduced corneal cylinder by an average of almost 6 diopters one week later. Average corneal cylinder was 5.1 diopters nine to 12 months after surgery. Best-corrected visual acuity with spectacles improved by an average of two Snellen lines (20/60 to 20/40) and uncorrected visual acuity improved by an average of one line (20/300 to 20/200). There were no complications related to placement of the sutures. This procedure provides a rapid and simple method for reducing astigmatism after penetrating keratoplasty.

Astigmatism↗
PubMed1989

The topography of normal corneas.

Previously we have analyzed photokeratographs to determine the topography of congenital, acquired, and surgically induced deformations of corneal shape. In this article, we survey the variety of corneal shapes found in both eyes of 22 individuals with normal corneas. The degree of correlation of the distribution of corneal power around the visual axis was striking for both eyes of 18 of the 22 individuals, as was the variability of the corneal topography of different individuals. The average centrally weighted corneal power determined from the photokeratographs correlated well with the average keratometric corneal power (r = .96). By defining the topographic features characteristic of normal corneas, we will be better able to diagnose corneal shape anomalies and understand the role such anomalies play in the degradation of vision.

Cornea↗
PubMed1989

One-year follow-up of epikeratophakia for keratoconus.

We report 1-year follow-up findings on 42 of the first epikeratophakia procedures performed for keratoconus at the Helsinki University Central Hospital. Altogether 40 patients (42 eyes) received epikeratophakia grafts to flatten their cones. The age of the patients ranged between 19 and 44 years. The mean follow-up for these patients was 10.7 +/- 4.4 months, and in 12 patients follow-up extended to over 12 months. Overall, the success rate for the procedure was 93%, and with repeated surgery it was 97% for all patients; in all patients uncorrected visual acuity improved. Preoperatively 82% of the patients had uncorrected acuity worse than 20/400, while all patients followed for 1 year had uncorrected visual acuity better than 20/400. At 6 and 12 months postoperatively best corrected visual acuities were all returned to within one line of their preoperative best corrected acuity; in 83% acuities were 20/40 or better 12 months postoperatively. Four patients out of 12 followed for 1 year needed no postoperative overrefraction at all. The mean flattening by keratometry readings was 9.8 diopters (D) and the mean decrease in myopia in terms of spherical equivalent was 5.3 D. The degree of irregular astigmatism was measured in five cases using LSU topographical corneal shape analysis, and showed that the mean preoperative irregular astigmatism of 3.9 D was reduced to 1.3 D in the long-term analysis. One case report is presented to show in detail the topographical changes induced by epikeratophakia in keratoconus. The noninvasive nature of the epikeratophakia procedure makes it a safe and desirable option for the treatment of keratoconus.

Adolescent↗
PubMed1989

Mechanism of chloride uptake in rabbit corneal epithelium.

The mechanism of chloride uptake at the basal membrane (stromal side) of rabbit corneal epithelium was examined by observing the effects of ion transport inhibitors and ion concentrations on the stimulated epithelial short-circuit current (Isc). Loop diuretics inhibited the theophylline-stimulated peak and sustained Isc. Treatment with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 0.2 mM) and/or 5-(N,N-dimethyl)amiloride (0.1 mM) as well as the potent anion exchange inhibitor, 5c(+)[(2,3,9,9a-tetrahydro-1H-fluoren-7-yl)oxy]acetic acid (0.01 mM), had no significant effect on Isc. These results are consistent with Cl- uptake by a Na+-Cl- or Na+-K+-2Cl- cotransport mechanism rather than Cl(-)-HCO3(-)-OH- exchange coupled to Na+-H+ exchange. Incubation in low [Na+] or [Cl-] before stimulation with forskolin (0.1 mM) reduced both peak and sustained Isc, and saturation kinetics were exhibited. Hill coefficients for [Na+] and [Cl-] were 0.99 and 1.04, respectively, for peak Isc and 0.66 and 1.18, respectively, for sustained Isc. Apparent ion affinities for Na+ and Cl- were 13.5 and 18 mM, respectively, for peak Isc and 15 and 22 mM, respectively, for sustained Isc. These results favor Cl- uptake by a 1 Na+:1 Cl- cotransport mechanism for the rabbit corneal epithelium, but involvement of K+ in this process has not been eliminated.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

Imaging of the cornea.

The aim of the LSU Eye Center Corneal Topography Project was to apply computer analysis to keratoscopy and develop graphic presentation methods to provide accurate and easily assimilated information regarding the status of patient corneal topography. The analysis contains four diagrams: a plot of the raw keratoscope data for quality control, a three-dimensional wire model of corneal surface power distribution, a plot of dioptric point surface powers, and a color-coded contour map of corneal surface powers. While the analysis uses a current generation 11 ring keratoscope for producing keratoscope photographs, it can be adapted to newer keratoscopes, which promise to give broader coverage of the corneal surface. Examples of normals and several surgical patients will be shown, including cases in which the method has pointed to potential refinements in the theory and application of refractive surgical techniques.

Adult↗
PubMed1987

Corneal topography in myopic patients undergoing epikeratophakia.

We analyzed the corneal topography of eight eyes in seven patients who had undergone myopic epikeratophakia, using a 1.5-mm graft/host disparity. Topographic maps of corneal power generated by computer analysis of keratoscope photographs disclosed a central spherical optical zone smaller in diameter than was predicted by the preoperative lathing measurements. Outside this optical zone, the dioptric power of the graft surface increased steadily, indicating a progressive steepening of the corneal slope as the graft/host interface is approached. This pattern occurred in patients with accurate and inaccurate refractive results. The center of the graft was noted in some cases to be decentered from the patient's visual axis. The corneal topography analysis system has made clear the need to maximize the diameter of the effective optical zone.

Cornea↗