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K Zadnik

Publications and source records attributed to K Zadnik.

At least 91 records · Page 5Linked to original sources
PubMed1993

Comparison of cyclopentolate versus tropicamide cycloplegia in children.

This double masked study compares the cycloplegic effects of tropicamide 1% and cyclopentolate 1% in 20 nonstrabismic, nonamblyopic, hyperopic 6- to 12-year-old children with a mean refractive error = +1.48 +/- 1.10 diopters (D). Unlike previous studies which used only amplitude of accommodation to measure the depth of cycloplegia, this study compares refractive error as determined by retinoscopy, distance subjective refraction, and distance autorefraction (Canon R-1). In addition, we compare the amplitude of accommodation as measured by subjective push-up and objective autorefraction methods. There is no statistically significant difference between cyclopentolate and tropicamide for either cycloplegic retinoscopy or distance subjective refraction. Autorefraction measurement of refractive error shows a statistically significant but clinically unimportant bias (0.14 +/- 0.30 D) toward more hyperopia with cyclopentolate. Both drops reveal latent hyperopia, and the mean latencies are not statistically different between the two cycloplegic agents. Latent hyperopia is not systematically related to the degree of hyperopia after tropicamide, but this relation is significant after cyclopentolate. No differences were found between refractive results with either agent at 30 min compared to 60 min after drop instillation. When measured objectively with the autorefractor, accommodation is inhibited more effectively by cyclopentolate than by tropicamide. Our results suggest that although tropicamide is not as effective as cyclopentolate in inhibiting accommodation it is, nevertheless, a useful cycloplegic agent for measuring distance refractive error of low to moderate hyperopia in school-aged children.

Accommodation, Ocular↗
PubMed1992

Retinoscopic measurement of the refractive state of the rat.

Using retinoscopy, we measured the refractive state of 96 eyes of three different strains of rats: albino Sprague-Dawley, Royal College of Surgeons (RCS) with and without inherited retinal dystrophy, and lean and obese varieties of Zucker rats. Contrary to previous reports, we do not find consistent high hyperopia in the rat, but rather refractions that range from near emmetropia (-0.12 D) to extreme hyperopia (+18.95 D). This range of refractive errors suggests a poorly developed emmetropization mechanism in the rat, and that individual refractions should be performed on animals utilized in experiments where refractive state is critical.

Albinism, Ocular↗
PubMed1992

A video technique for phakometry of the human crystalline lens.

Accurate measurement of the dioptric power of the human crystalline lens is important in any study of ocular development and refractive error. Previous studies have used comparison ophthalmophakometry, measuring crystalline lens curvature and power from still flash photographs of Purkinje images I, III, and IV. This report presents a video-based technique for in vivo measurement of crystalline lens power suitable for use with children. The repeatability and validity of this video system were evaluated in comparison to a still photograph system through the measurement of anterior and posterior lens curvatures of 40 normal adults. The video system's repeatability (95% limits of agreement) was +/- 0.52 diopters for the anterior lens power, +/- 0.73 D for the posterior lens power, and +/- 0.88 D for the total lens power. The repeatability of the still flash photography system was +/- 0.78 D for the anterior, +/- 1.43 D for the posterior, and +/- 1.84 D for the lens power as a whole. An indirect method of calculating lens power using other ocular component measures gave a repeatability of +/- 1.78 D. The validity of the video system was improved by having the camera and the light source closer to the optic axis of the eye. The bias induced by having a more off-axis configuration (40 degrees separation between camera and light source) was a +0.10 D overestimation of surface power for the anterior and +0.73 D for the posterior lens surface power compared to a more coaxial arrangement (20 degrees between camera and light source). The use of video phakometry improved the repeatability and the validity of lens curvature measures relative to still flash photograph comparison ophthalmophakometry and to an indirect method of calculating lens power. This was achieved through the system's ability to analyze multiple frames, the use of a collimated light source, and the placement of the light source for the Purkinje images closer to the eye's optic axis.

Adult↗
PubMed1992

The repeatability of measurement of the ocular components.

Studies of the ocular components of refraction typically neglect issues of repeatability of measurement methods or analyze method comparison/repeatability data inappropriately using correlation. The authors have examined the repeatability of refractive error measures (retinoscopy, subjective refraction, and Canon R-1 autorefraction, noncycloplegic and cycloplegic), axial dimension measures (Allergan-Humphrey A-scan ultrasound), and corneoscopy (keratometry and KERA photokeratoscopy), and the agreement between different refractive error and corneal measurement methods on 40 pre-presbyopic normal adults. The authors plotted the difference versus the mean of two different measurement occasions (repeatability), or two different methods (agreement), to determine the bias (mean of the differences relative to zero) and 95% limits of agreement of each technique. The most reliable measure of refractive error was autorefraction with cycloplegia, with 95% limits of agreement of +/- 0.32 diopters. Cycloplegic autorefraction had no statistically significant bias compared to cycloplegic subjective refraction. Cycloplegic retinoscopy was the least reliable refractive error measure, with repeat measures on two separate occasions extending over 95% limits of agreement of +/- 0.95 D. Anterior chamber depth was reliable to +/- 0.29 mm, lens thickness to +/- 0.20 mm, and vitreous chamber depth to +/- 0.37 mm. Corneal curvature measures show keratometry to be more reliable (to +/- 0.87 D) than photokeratoscopy (+/- 2.02 D) with a statistically significant bias (paired t-test, P less than 0.0001) of 0.57 D flatter for photokeratoscopy.

Adult↗
PubMed1992

Myopia and refractive error in dogs.

The refractive error of 240 phakic dogs of various breeds was measured using streak retinoscopy and averaged (-0.27 +/- 1.41 D relative to infinity). Analysis by breed showed that the German Shepherd, Rottweiler, and Miniature Schnauzer breeds had an increased prevalence of myopia with an average refractive error of -0.86 +/- 1.31 D, -1.77 +/- 1.84 D, and -0.66 +/- 1.05 D, respectively. Myopia also was found in older dogs with marked nuclear sclerosis of the crystalline lens. Fifty-three percent of all German Shepherd dogs in a veterinary clinic population (n = 58 eyes) had a myopic refraction of greater than or equal to -0.50 D; 64% of all Rottweiler dogs (n = 28 eyes) were myopic. An in-depth investigation of German Shepherd dogs, using A-scan ultrasonography, photokeratoscopy, and streak retinoscopy, was done at Guide Dogs for the Blind (San Rafael, CA). By contrast with the results obtained in the veterinary clinic population, the overall average refractive error of guide dog German Shepherd dogs (n = 106 eyes) was +0.19 +/- 0.81 D, and only 15% of these dogs were myopic. The axial length and corneal curvature of myopic eyes did not differ significantly from nonmyopic eyes.

Animals↗
PubMed1988

Contrast sensitivity after epikeratophakia.

Epikeratophakia is a rapidly evolving surgical procedure for the refractive correction of aphakia. Even when Snellen acuity after epikeratophakia is normal, patients often report a subjective degradation of the visual image through the surgically corrected eye. To further define visual performance in the patient with optically successful epikeratophakia, we examined contrast sensitivity in two patients surgically corrected for monocular aphakia. Contrast thresholds were measured over a range of spatial frequencies using both computer-generated sinusoidal gratings and a commercially available wall chart system. The eye with epikeratophakia in each case was compared with the opposite normal eye with comparable acuity. One patient was also tested prospectively in the same eye both before and after surgery. Data demonstrate a depression of the contrast sensitivity function in the middle and high spatial frequencies induced by the placement of an epikeratophakia lenticule when compared with the normal eye or contact lens-corrected, preoperative aphakic eye with comparable good acuity. These findings may explain the subjective experience of epikeratophakia patients.

Adult↗
PubMed1987

Personality trends in keratoconus. An analysis.

Patients with keratoconus frequently are described as having peculiar personality characteristics, despite the lack of controlled studies in the ophthalmologic or psychiatric literature. We studied 109 subjects, using a standardized personality inventory (the Millon Clinical Multiaxial Inventory) that measures 20 personality scales-both normal and pathologic. Subjects were divided into three age-matched groups: (1) patients with keratoconus, (2) patients with other chronic eye diseases, and (3) normal controls. Results indicated that although chronic eye disease, including keratoconus, did have an impact on personality functioning in young and middle-aged adults, no specific complex of personality characteristics attributable to keratoconus could be identified. Patients with keratoconus differed from normal controls in much the same way as did patients with other chronic eye diseases, being less conforming and more passive-aggressive, paranoid, and hypomanic. They tended to more disorganized patterns of thinking and scored higher on substance abuse indicators. The influence of keratoconus on personality may be a function of the timing and nature of its onset in the context of the patient's psychosocial development.

Adolescent↗
PubMed1987

Contrast sensitivity after penetrating keratoplasty.

Contrast sensitivity testing in the corneal transplant patient may enhance our assessment of visual performance, which is traditionally evaluated using Snellen acuity only. To evaluate contrast sensitivity function after penetrating keratoplasty, we studied 29 patients with anatomically successful corneal grafts and a best corrected visual acuity of 20/50 or better. Graft patients were compared with an age-matched control group including persons with comparable visual acuities without ocular disease. In addition to a complete ophthalmic examination, all subjects underwent contrast sensitivity testing using a computer-generated sinusoidal grating system as well as a commercially available contrast sensitivity wall chart. Data indicate that, despite comparable Snellen visual acuity, the contrast sensitivity curves for graft patients were depressed overall compared with those of normal subjects except at the lowest spatial frequency. However, comparison of grafted eyes to contralateral eyes with corneal disease in a small subset of patients with bilateral disease shows a trend toward higher contrast sensitivity values in the eyes that had been operated on. These data suggest that despite an improvement in contrast sensitivity with penetrating keratoplasty, an eye with a corneal transplant is not entirely normal from a visual standpoint. Nonacuity parameters may be important indexes for assessing real-world visual function in the graft patient, although the clinical role of these tests is not yet completely defined.

Adult↗
PubMed1987

Cataracts, chronic uveitis, and retinal vasculitis in Behçet's disease.

A 13-year-old Iranian male presented with the diagnosis of Behçet's disease, a systemic disease accompanied by significant anterior and posterior segment inflammation. He had had bilateral lensectomies, which necessitated aphakic soft contact lens fitting. Such optical enhancement of the patient's visual performance in Behçet's disease is an essential part of the overall patient management.

Adolescent↗
PubMed1987

Refractive error changes in law students.

We report two separate studies: a retrospective survey and a longitudinal study; both were designed to assess the changes in refractive error of a group of young adult law students. The retrospective survey compared the previous spectacle correction to the current refractive error in the ocular examination records of 87 members of the class of 1982 law students who were examined at the University of California, Berkeley School of Optometry. Forty-one students (47.1% of the sample, 12.9% of the entire class of 318) increased at least -0.50D in myopia in at least one eye. In the longitudinal study, we followed 16 first year law students for 6 months, measuring refractive error. Five eyes (15.6%) became at least +0.50D more hyperopic, and 12 eyes (37.5%) became at least -0.50D more myopic. These data represent analysis of a small number of eyes over a short period of time. An adult myopic shift is nonetheless evident. A methodology for accumulation of more meaningful data on the specific ocular component changes responsible for this effect is discussed.

Adult↗
PubMed1987

Rapid contrast sensitivity assessment in keratoconus.

Contrast sensitivity derangement may accompany keratoconus even in the presence of normal or near normal Snellen visual acuity. This has been demonstrated with computer-driven contrast sensitivity test devices. The purpose of this study was to evaluate the utility and efficacy of rapid screening devices for contrast sensitivity testing. However, such devices are often cumbersome and difficult to use clinically. We tested 12 patients with keratoconus on 2 simple chart systems designed to test contrast sensitivity in a rapid and clinically useful manner: the Vistech chart and the Regan multi-contrast visual acuity charts. Both devices detected the contrast sensitivity abnormalities present in early keratoconus, but some patients [with greater than or equal to 6/12 (20/40) visual acuity] were unable to respond to areas of the charts corresponding to high spatial frequency and/or low contrast tasks. Such simple wall charts may be useful in measuring the visual abnormalities in early keratoconus, in monitoring the progression of the disease, and in evaluating various treatment options.

Adult↗
PubMed1987

Contact lens fitting relation and visual acuity in keratoconus.

The presence of visual decrement in keratoconus is widely recognized, but little is known about the effect of different contact lens fitting philosophies on visual acuity. We studied 10 eyes with keratoconus, each of which was tested with an automated visual acuity device while wearing rigid contact lenses of varying base curves and diameters. Lenses used were large, flat lenses and small, steep lenses, fitted from 0.4 mm flatter to 0.4 mm steeper than the average keratometric measurement in 0.1-mm increments, including parallel to the average corneal curvature. A small improvement in visual acuity was noted with the flat lenses, equalling approximately one-half line of visual acuity, which, although statistically significant, was not deemed to be clinically significant. In addition, a decrement in visual acuity of keratoconus patients with centrally placed cones was noted and is discussed.

Contact Lenses↗
PubMed1987

Fabry's disease.

Explore the source record for details and available documents.

Amiodarone↗
PubMed1986

Photorefraction with a catadioptric lens. Improvement on the method of Kaakinen.

Kaakinen (1979) presented a method of measuring refractive error and ocular alignment by simultaneous photography of corneal and fundus reflexes. As presented, the technique was unable to detect refractive errors of less than 2-3 diopters (Howland 1980; Kaakinen 1979). We demonstrate that the use of a catadioptric lens and a long working distance can improve sensitivity to less than 1.0 D. Refractions of a model eye, an accommodating eye and ametropic eyes indicate that refractive errors greater than 0.75 D are readily detectable. The improvement in sensitivity achieved by the present system is attributable to a reduction of the angle between the flash source and the entrance pupil of the photorefractor.

Accommodation, Ocular↗
PubMed1984

The effect of penetrating keratoplasty on contrast sensitivity in keratoconus.

Complaints of visual distortion often precede a decrement in visual acuity in keratoconus. We studied seven patients with keratoconus who had undergone keratoplasty in one eye and whose Snellen visual acuity measurements were equal in the grafted and nongrafted eyes. Subjects were examined clinically; we then measured contrast thresholds for seven spatial frequencies of computer-generated sinusoidal gratings after optimal contact lens correction. Results indicate that nongrafted keratoconic eyes demonstrate abnormal contrast sensitivity, even with good visual acuity measurements. Eyes with clear corneal grafts and with visual acuities comparable to nongrafted eyes fell within the 95% confidence limits of the normal contrast sensitivity curve. The findings confirm that corneal distortion or opacity in the optimally corrected keratoconic eye may account for notable visual dysfunction and that keratoplasty improves not only Snellen visual acuity but contrast sensitivity as well.

Adult↗
PubMed1984

Effect of luminance, contrast, and eccentricity on visual acuity in senile macular degeneration.

We examined the effect of luminance on low contrast visual acuity in six patients with mild reductions in vision due to senile macular degeneration (SMD) and in six normals of approximately the same age. At the highest luminance tested the SMD patients showed a reduction in acuity compared to the controls, with eccentricity and contrast effects clearly shown. The SMD patients had difficulty performing the acuity task at the lower luminances (0.26 and 0.75 cd/m2); they showed little or no increase in visual acuity with increasing contrast levels at the lower luminances. Acuity was slightly influenced by target eccentricity at these luminances. These data suggest that the adaptation mechanisms allowing the normal visual system to operate efficiently over a wide range of luminances are affected in SMD, even when clinically measured acuity is only moderately depressed.

Aged↗