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K Zadnik

Publications and source records attributed to K Zadnik.

At least 19 recordsLinked to original sources
PubMed1999

Cycloplegia in African-American children.

PURPOSE: The selection of a cycloplegic agent depends on the desired outcome, the characteristics of the patient receiving the drug, and the associated risks. The Orinda Longitudinal Study of Myopia (OLSM) has used 1% tropicamide to assess the ocular components and cycloplegic refractions in a large cohort of predominantly Caucasian children. Although tropicamide has provided adequate cycloplegia and mydriasis for the OLSM cohort, conventional clinical wisdom and scientific investigations have suggested that tropicamide might not produce adequate cycloplegia and mydriasis for subjects with darker iris pigmentation. In this study one drop of 1% tropicamide followed by one drop of 1% cyclopentolate was used to determine their effectiveness in producing adequate cycloplegia and mydriasis for cycloplegic refraction and ocular component measurements in a group of African-American children. METHODS: Nineteen children [age range 5.5 to 15.6 years, mean 8.4 years +/- (SD) 2.5 years] were tested at Family HealthCare of Alabama, Eutaw, AL. Their accommodative responses were measured using a Canon R-1 autorefractor prior to and at 30, 45, and 60 min after instillation of one drop of 0.5% proparacaine, 1% tropicamide (Mydriacyl), and 1% cyclopentolate (Cyclogyl) in both eyes. A target of 20/155 letters in a 4x4 grid positioned behind a +6.50 diopter (D) Badal lens provided accommodative stimuli of 1.00 D, 2.00 D, and 4.00 D. RESULTS: All results are presented as mean +/-1 SD. Pupils, measured from video frames, dilated rapidly and maximally at 30 min after instillation of eye drops (7.3+/-0.5 mm) Predilation, the mean accommodative responses were 0.17+/-0.29 D for the 1.00 D stimulus, 1.01+/-0.40 D for the 2.00 D stimulus, and 2.77+/-0.74 for the 4.00 D stimulus. At 30 min after drop instillation, the responses were 0.07+/-0.14 D for the 1.00 D stimulus, 0.36+/-0.35 D for the 2.00 D stimulus, and 0.77+/-0.61 for the 4.00 D stimulus. Results were very similar at 45 and 60 min after drop instillation. CONCLUSIONS: Combining 1% tropicamide and 1% cyclopentolate was very effective in providing both cycloplegia and mydriasis adequate for ocular biometry and cycloplegic refractions 30 min after drop instillation in African-American children.

Accommodation, Ocular↗
PubMed1999

Corneal scarring in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study: baseline prevalence and repeatability of detection.

PURPOSE: The multicenter Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a prospective, observational study of 1,209 keratoconus patients. We report on the prevalence of corneal scarring in these patients. We also report on the test-retest repeatability of corneal scar documentation at the slit-lamp biomicroscope by trained clinicians and by masked photograph readers and on the scarring-status agreement at baseline between clinicians and photograph readers. METHODS: Clinicians and masked photograph readers graded each cornea as to scarring status. Patients were examined by clinicians, and their corneas were photographed at baseline (2,297 nongrafted eyes of 1,209 patients) and at a repeated visit (258 nongrafted eyes of 138 patients). These photographs were evaluated by the masked readers at the CLEK Photography Reading Center (CPRC). Clinicians reported corneal scars in right eyes at baseline as "definitely not present" in 53.9%, "probably not present" in 8.4%, "probably present" in 8.2%, and "definitely present" in 29.4% of patients. A weighted kappa statistic of 0.83 (95% confidence interval from 0.78 to 0.88) indicates that agreement is excellent between baseline and repeated assessments for the presence of a corneal scar by clinicians. RESULTS: Agreement is very good between baseline and repeated photograph-reader assessments for the presence of a scar, with a weighted kappa of 0.77 (95% confidence interval, 0.72-0.82). The kappa statistic comparing photograph-reader scarring assessments with clinician results was 0.69 (95% confidence interval, 0.66-0.71). CONCLUSION: The data also suggest better agreement between clinicians and readers when Vogt's striae and corneal nerves were observed. The data also suggest better agreement when corneal staining was not observed by the photograph readers. The CLEK Study protocol for determining the presence of scars is highly repeatable.

Cicatrix↗
PubMed1998

The effect of continuous light on refractive error and the ocular components of the rat.

Phototoxic induced degeneration of the rat retina is a well-documented phenomenon resulting in losses of photoreceptors and their cell bodies, and an overall retinal thinning. This process may serve as a test of the hypothesis that the retinoscopic reflex originates from the inner limiting membrane of the retina. Retinal thinning should produce myopia in the absence of any other ocular component changes in a stable, mature eye if the inner limiting membrane model is correct. Phototoxic retinal degeneration was induced in 10 albino rats by exposure to 19 days of continuous light (1,800 cd m-2). Another 10 albino rats exposed to 12-hr on/12-hr off cycled light served as controls. Before and after the exposure to constant light, measures were made of refractive state by cycloplegic retinoscopy, corneal curvature and lens curvature by Purkinje image photography, and axial length of the globe by A-scan ultrasonography. Comparing pre- to post-exposure values, phototoxic degeneration resulted in a mean (+/- S.D.) myopic shift of -5.10 +/- 2.12 D (P < 0.002). The corneal curvature also steepened significantly (0.17 +/- 0.11 mm, equivalent to -6.0 D; P < 0.004), while the posterior curvature of the crystalline lens flattened by 0.21 +/- 0.22 equivalent mm (P < 0.027), and the axial length shortened by 0.11 +/- 0.11 equivalent mm (all tests Wilcoxon signed-rank; P < 0.025). Phototoxic rats underwent a mean retinal thinning of 49.6 mu compared to controls (Kruskal-Wallis test; P < 0.0008). No refractive or ocular parameters changed significantly in the controls. Phototoxic degeneration in the rat has optical consequences beyond simple retinal thinning. The size of the eye and the curvature of refractive surfaces can be altered in a mature eye well after the completion of development. The multiple changes which occur prevent phototoxic retinal thinning from serving as a test of the inner limiting membrane model for retinoscopic reflections.

Animals↗
PubMed1998

Visual acuity repeatability in keratoconus: impact on sample size. Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group.

PURPOSE: The purpose of this paper is to determine the repeatability of visual acuity measurement in keratoconus and to describe the impact of measurement repeatability on sample size. METHODS: Approximately 10% of a 1209 patient sample in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study were selected randomly for a Repeat CLEK Study Visit. Patients were tested at the 15 CLEK Participating Clinics. The test-retest sample consisted of 1 34 keratoconus patients who met the entry criteria of the CLEK Study. High and low contrast Bailey-Lovie visual acuity was measured with the patient's habitual visual correction (entrance visual acuity monocularly and binocularly), and with the best correction monocularly (either the patient's rigid contact lens and over-refraction, or with a CLEK Study trial lens and appropriate over-refraction) at two visits separated by a median of 90 days (range 22 to 268 days). RESULTS: The mean absolute differences between the number of letters correct at the two visits ranged from a low of 3.24 +/- 3.1 for entrance high contrast binocular acuity to a high of 5.48 +/- 5.1 for best corrected low contrast monocular acuity. Intraclass correlation coefficients ranged from 0.757 to 0.853. The visual acuity score was somewhat higher at the Repeat Visit than at the Baseline Visit when the examiners were different between visits. CONCLUSIONS: Given the variable vision reported by keratoconus patients, visual acuity in this sample was very repeatable. Repeatability was slightly poorer when different examiners tested visual acuity at the Baseline and Repeat Visits.

Adolescent↗
PubMed1998

Development of phoria in children.

BACKGROUND: Although the prevalence of phoria in adults is well documented, data are scarce on phoria in children. We present results using modified clinical technique vision screening and data from the Orinda Longitudinal Study of Myopia on a large, population-based sample of nonstrabismic children to document the prevalence of phoria with age. METHODS: We collected cross-sectional (N = 1495) and longitudinal (N = 469) data. Phoria data were collected by cover tests administered by one observer who subjectively classified phoria as orthophoria, esophoria, or exophoria in 2 delta steps. RESULTS: Ninety-seven percent of the children were orthophoric at distance, and there were no significant changes with age. Near phoria showed a more normal distribution, with a 10.8% decrease in the prevalence of exophoria (from 31.8 to 21.0%) and a 5.5% increase in the prevalence of esophoria (from 6.7 to 12.2%) between kindergarten and fifth grade. CONCLUSIONS: Children are typically orthophoric or exophoric at near, but convergent shifts occur with age.

Child↗
PubMed1998

Inter-clinician agreement on clinical data abstracted from patients' medical charts.

PURPOSE: The purpose of this study was to determine the inter-observer repeatability of retrospective chart reviews. METHODS: Retrospective abstraction of corneal transplant patients' medical records by two independent observers was performed at the University of California, Davis, Department of Ophthalmology, Sacramento, CA. The sample consisted of 100 consecutive patients who underwent penetrating keratoplasty, and the primary outcome measure was the degree of agreement between the 2 independent observers on clinical ocular data abstracted from patients' medical charts. RESULTS: Even when given specific criteria for abstraction of data from patients' medical charts, inexperienced but trained observers exhibited a small degree of disagreement (range 0 to 12%) on patient demographic variables (e.g., gender, age, and date of birth) to be used for data analysis. Larger amounts of disagreement (range 3 to 26%) were found on frequently occurring variables (e.g., predisposing ocular conditions, surgical complications, and classification of corneal staining). CONCLUSIONS: Based on these data, inter-observer repeatability for retrospective chart review studies is good, but investigators using this study methodology must be quite specific about the data to be collected and should be aware of standardization techniques to enhance observer repeatability.

Abstracting and Indexing↗
PubMed1998

Repeatability of refraction and corrected visual acuity in keratoconus. The CLEK Study Group. Collaborative Longitudinal Evaluation of Keratoconus.

PURPOSE: The purpose of the test-retest phase of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study was to determine the repeatability of the various parts of the CLEK Study protocol. This paper presents the test-retest parameters of the refraction protocol. METHODS: We examined 138 CLEK Study-eligible patients on two occasions (median, 90 days; range, 22 to 268 days). All patients underwent subjective refraction on two occasions, and contact lens over-refractions were performed either over the patient's habitual rigid contact lenses or over a trial rigid contact lens equal in base curve to the steep keratometric reading in nonrigid contact lens wearers. RESULTS: Mean interoccasion differences +/- SD were -0.32 +/- 2.91 D and -0.17 +/- 1.39 D for subjective refraction sphere and cylinder power, respectively, and the mean absolute difference for subjective refraction cylinder axis was 18.1 +/- 20.2 degrees. The mean interoccasion difference +/- SD for high-contrast visual acuity with subjective refraction was 0.38 +/- 10.9 letters correct. Mean interoccasion differences +/- SD were -0.11 +/- 0.81 D and 0.02 +/- 0.67 D for contact lens over-refraction sphere and cylinder power, respectively, and the mean absolute difference for contact lens over-refraction cylinder axis was 11.6 +/- 9.9 degrees. The mean interoccasion difference +/- SD for visual acuity with contact lens over-refraction was 0.50 +/- 5.2 letters correct and 0.71 +/- 6.9 letters correct for high- and low-contrast visual acuity, respectively. CONCLUSIONS: The repeatability of subjective refraction in keratoconus patients is good but somewhat lower than that found in nondiseased eyes. Only 36% of our repeat measures of sphere power from subjective refraction fell within 0.50 D of each other, compared with more than 90% in studies of normal eyes.

Adult↗
PubMed1998

Optical and structural development of the crystalline lens in childhood.

PURPOSE: To document the development of key optical and structural parameters of the crystalline lens throughout childhood and examine possible mechanisms by which lens power remains coordinated with the growth of the eye to maintain emmetropia. METHODS: Using cycloplegic autorefraction, video-based phakometry, and ultrasonography, the authors measured refractive error and crystalline lens parameters in 994 children in the first through eighth grades, who participated in the Orinda Longitudinal Study of Myopia, between one and five times from 1989 through 1993. Polynomial growth curves were fit to the data by maximum likelihood estimation. The average annual rates of change in each parameter from each subject's longitudinal data were also estimated. RESULTS: The lens radii of curvature flattened throughout childhood, yet decreases in lens equivalent power stopped after 10 years of age. This indicates that the refractive index of the lens increased during later childhood. Lens thinning in early childhood also ceased after 10 years of age. The spherical volume of the lens showed no appreciable net increase, but the axial length of the eye continued to grow throughout childhood. The prevalence of myopia in our data increased sharply at age 10 years, reaching 21.3% by the age of 14 years. CONCLUSIONS: Concurrent thinning and flattening of the crystalline lens imply that the lens is mechanically stretched by the equatorial growth of the eye during childhood. Changes in the patterns of lens development near the age of 10 years, concurrent with the onset of myopia, suggest that forces arise which interfere with equatorial growth. Such forces might diminish the decreases in lens power and amplify axial elongation to promote myopia.

Adolescent↗
PubMed1998

Repeatability and agreement of two corneal-curvature assessments in keratoconus: keratometry and the first definite apical clearance lens (FDACL). CLEK Study Group. Collaborative Longitudinal Evaluation of Keratoconus.

PURPOSE: This study was conducted to determine the agreement and test-retest repeatability of two methods for measuring corneal curvature in keratoconus: keratometry and the First Definite Apical Clearance Lens (FDACL). Our interest in the FDACL procedure stems from the important contact lens-fitting information and documentation of disease progression provided by the FDACL trial lenses and observation of fluorescein patterns. METHODS: The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is an observational study that has enrolled 1,209 keratoconus patients to characterize the progression of keratoconus, to determine factors associated with its progression, and to assess its impact on quality of life. Ten percent of the patients were randomly selected at baseline for a retest examination. The baseline examination, which included keratometry and FDACL, was repeated in this sample. The FDACL is the flattest lens in the standardized CLEK trial lens set that vaults the apex of the cone. FDACL provides an estimate of the sagittal height of the cone. RESULTS: The correlation of FDACL with the steep keratometric reading (r = 0.89; p = 0.0001) and the flat keratometric reading (r = 0.83; p = 0.0001) were high. Test-retest repeatability as measured by the intraclass correlation coefficient (ICC) was high: FDACL ICC, 0.97; steep keratometric reading ICC, 0.96; and flat keratometric reading ICC, 0.95. Test-retest repeatability of FDACL remained high in advanced disease. CONCLUSION: FDACL provides a repeatable new procedure for determining disease severity in keratoconus.

Adult↗
PubMed1998

Retinoscopy.

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Diagnostic Techniques, Ophthalmological↗
PubMed1998

Baseline findings in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study.

PURPOSE: To describe the baseline findings in patients enrolled in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. METHODS: This is a longitudinal observational study of 1209 patients with keratoconus enrolled at 16 clinical centers. Its main outcome measures are corneal scarring, visual acuity, keratometry, and quality of life. RESULTS: The CLEK Study patients had a mean age of 39.29+/-10.90 years with moderate to severe disease, assessed by a keratometric-based criterion (95.4% of patients had steep keratometric readings of at least 45 D) and relatively good visual acuity (77.9% had best corrected visual acuity of at least 20/40 in both eyes). Sixty-five percent of the patients wore rigid gas-permeable contact lens, and most of those (73%) reported that their lenses were comfortable. Only 13.5% of patients reported a family history of keratoconus. None reported serious systemic diseases that had been previously reported to be associated with keratoconus. Many (53%) reported a history of atopy. Fifty-three percent had corneal scarring in one or both eyes. CONCLUSIONS: Baseline findings suggest that keratoconus is not associated with increased risk of connective tissue disease and that most patients in the CLEK Study sample represent mild to moderate keratoconus. Additional follow-up of at least 3 years will provide new information about the progression of keratoconus, identify factors associated with progression, and assess its impact on quality of life.

Adult↗
PubMed1997

The artifact of retinoscopy revisited: comparison of refractive error measured by retinoscopy and visual evoked potential in the rat.

PURPOSE: The validity of retinoscopy in small eyes has not been clearly established due to uncertainty regarding the source of the ocular reflections assessed during this procedure. A widely cited model which proposes that their origin is the inner limiting membrane of the retina was evaluated in the rat by comparing refractive errors measured by retinoscopy to those measured by visual evoked potentials (VEPs). METHODS: Ten rats were refracted both by cycloplegic streak retinoscopy and by VEP while viewing 0.05 to 0.15 cpd square-wave gratings-reversed at 1.875 Hz. Spherical aberration of the rat eye was assessed as a potentially confounding variable in VEP refraction by sequential retinoscopic refractions across the rat's natural pupil through a 1.5-mm pinhole. RESULTS: All animals were moderately to highly hyperopic by both methods (range = +4.5 to +18.5 D). Spherical aberration was minimal (median = 3.5 D of overcorrected aberration). The median difference between retinoscopic refractions and those by VEP was not significant (+1.94 D more hyperopia by retinoscopy; p = 0.062, Wilcoxon signed rank) but was significantly less than the +9.64 D difference predicted by an inner limiting membrane model (upper 95% limit = +3.76 D). CONCLUSION: This suggests that the origin of the retinoscopic reflex is located in the outer retina rather than at the inner limiting membrane. Correction factors for retinoscopy in small eyes may be smaller than previously assumed.

Animals↗
PubMed1997

Comparison of corneal versus through-the-lid A-scan ultrasound biometry.

BACKGROUND: Accurate ultrasonography data on axial ocular dimensions in infants and toddlers are essential for understanding ocular development. Conventional methods using corneal contact with topical anesthesia but without sedation are not feasible for most of these patients. We evaluate an alternative method which places the probe on the closed eyelid. METHODS: We compared A-scan ultrasound biometry measurements taken with the probe directly on the cornea with those with the probe on the closed eyelid on the right eye of 35 young adult subjects. RESULTS: There was no significant difference between methods for mean anterior chamber depth (corneal = 3.83 mm, lid = 3.87 mm, p = 0.13, paired t-test). The mean lens thickness (corneal = 3.63 mm, lid = 3.75 mm, p = 0.0001, paired t-test) and mean vitreous chamber depth (corneal = 17.50 mm, lid = 17.68 mm, p = 0.0440, paired t-test) were significantly different. CONCLUSION: Ultrasonography through the closed eyelid appears to be a viable method with acceptable validity compared with corneal ultrasound. Poorer agreement for lens thickness and vitreous chamber depth may be undesirable, but these data should be useful for planning future studies of infants and toddlers.

Adult↗
PubMed1997

Preoperative risk factors for surface disease after penetrating keratoplasty.

We sought to identify the types of, prevalence of, and predisposing factors for the development of surface keratopathy after penetrating keratoplasty. We reviewed the records of 120 corneal grafts performed over a 15-month period. Twenty patients were excluded from the study. Fifty-three men and 47 women composed the group studied. All transplants were performed by the same surgeon. Retrospective data from patients' records were gathered preoperatively and from postoperative visits at 1 week and at 1, 2, 3, and 4 months. Data included preoperative medical and demographic data, operative time, postoperative medication regimens, assessment of the presence and degree, if present, of punctate epithelial keratopathy (PEK), hurricane keratopathy, macroepithelial defects, microcystic edema, bullous edema, and filamentary keratitis. In addition, information on the donor material was recorded. Surface disease and normal groups were compared to identify risk factors for the occurrence of surface abnormalities. Thirty-three of the patients demonstrated persistent surface abnormalities. Coarse PEK was the most common surface abnormality in the sample studied and was most prominent in the first week after surgery. Postoperative surface keratopathy was not statistically associated with preoperative diagnosis, donor age, death-to-preservation time, preservation-to-surgery time, or donor epithelial status. However, corneal recipients in the group with surface keratopathy were significantly older (mean, 68.7 years) than patients in the group with no surface abnormalities (mean, 52.6 years; Mann-Whitney U test, p < 0.001). Although many factors may contribute to the normal integrity of the corneal surface after keratoplasty, recipient age is of key importance in the development of surface disease.

Aged↗
PubMed1997

Effect of optical defocus on visual acuity in dogs.

OBJECTIVE: To determine the effect of optical defocus (such as what develops in spontaneous myopia and subsequent to cataract extraction) on visual acuity in dogs. ANIMALS: 3 young adult male Beagles. PROCEDURE: The effect of optical defocus on visual acuity was determined by sweep visual evoked potential, using a within-subjects/repeated measures design in which each dog served as its own control. Dogs were positioned so that the eye being tested was 60 cm in front of the video display, and the target was centered on the area centralis. To create ametropia relative to the video screen, a series of concave and convex spherical lenses were placed 1 cm in front of the eye, and sweep visual evoked potential acuities were obtained. RESULTS: Maximal acuity was 7.0 to 9.5 cycles/degree. Defocusing by 2.0 diopters reduces Beagle grating acuity approximately 1 octave. Mimicking aphakia resulted in a marked depression of acuity to 0.7 cycles/degree or less. CONCLUSIONS: Even mild degrees of ametropia have appreciable impact on the resolving power of the canine visual system. CLINICAL RELEVANCE: Spontaneous myopia is encountered in dogs and may be associated with impaired visual performance attributable to a reduction in visual acuity. Previous reports indicate the possibility of myopia in dogs to have a heritable component. On the basis of our results, refractive correction of aphakia is advisable, and refractive screening of dogs with demanding visual tasks (eg, service dogs, field-trial Labrador Retrievers) is recommended.

Animals↗
PubMed1997

The Glenn A. Fry Award Lecture (1995). Myopia development in childhood.

PURPOSE: The Orinda Longitudinal Study of Myopia is a 12-year project examining predictive factors for the onset of myopia, the underlying etiologies of myopia, and normal eye growth in school children. METHODS: This paper reports on all measurements made of the ocular components (cycloplegic refractive error, corneal curvature, crystalline lens power, and axial ocular dimensions), parental history of myopia, and near work activity in children participating in the Orinda Longitudinal Study of Myopia between 1989 and 1993. An analysis of the interaction between parental history of myopia and children's near work is conducted on the cross-sectional study data from 1993. RESULTS: The cross-sectional and longitudinal data show a gradual decrease in refractive error from low hyperopia toward emmetropia, no shift in corneal curvature, a gradual decrease in crystalline lens power, thinning of the crystalline lens, and elongation of the eye between the ages of 6 and 14 years. Parental history is more contributory to a statistical model predicting myopia than is near work, but near work is a significant factor as well. We can find no evidence of statistical interaction between parental history and near work in explaining the presence or absence of myopia. CONCLUSIONS: The emmetropization process is evident in the gradual decrease in refractive error toward emmetropia, the axial elongation of the eye, and the compensating decrease in crystalline lens power. Both nature and nurture play a role in the etiology of myopia, although the predominant role appears to belong to a positive parental history of myopia. This role does not appear to be through an interaction between parental myopia status and children's near work activity.

Adolescent↗