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Biomedical subjects

T C Prager

Publications and source records attributed to T C Prager.

At least 19 recordsLinked to original sources
PubMed1992

Visual acuity correlates with severity of retinopathy of prematurity in untreated infants weighing 750 g or less at birth.

Visual acuity was assessed in 72 patients who weighed 750 g or less at birth, had intact visual pathways as confirmed with computed tomography or magnetic resonance imaging, and had at least one eye evaluated for cicatricial sequelae after active, untreated retinopathy of prematurity without macular detachment (stage 4a or better). Visual acuities were obtained for 137 untreated, sighted eyes. Severity parameters for retinopathy of prematurity (stage of retinopathy of prematurity, refraction [in spherical equivalents], macular ectopia [in disc diameters], and vessel traction [in 30 degrees sectors]) was were significant predictors of visual acuity (P less than .0001) based on results of linear regression and stepwise regression analyses; however, parameters of retinal immaturity (birth weight, gestational age, and zone of retinopathy of prematurity) were not significant predictors of visual acuity. Visual acuity of the study eyes was good (median, 20/30; geometric mean, 20/33.58), with no statistical differences between eyes evaluated on last examination with linear Allen figures and those evaluated with linear Snellen test types.

Child, Preschool↗
PubMed1992

Axial length in keratoconus.

Axial length is a major determinant of ocular refractive power that has not been well established for keratoconus eyes. The purpose of this study was to establish the mean and range of axial length among both keratoconus eyes with no previous surgery and postkeratoplasty keratoconus eyes, and to determine if there is a significant reduction of axial length following variations in surgical techniques in penetrating keratoplasty. The axial length of 157 keratoconus eyes with no previous surgery was measured using applanation ultrasonography. The mean axial length measurement was 24.39 (+/- 1.13 mm), with a range of 21.82-28.69 mm. The axial length of 66 postkeratoplasty keratoconus eyes was similarly measured. The mean axial length measurement was 24.10 (+/- 1.22 mm), with a range of 21.83-26.87 mm. These values are not significantly different from the axial length mean and range found among emmetropic eyes. A significant shortening of the axial length (F = 5.2, p = 0.04) was obtained in the postoperative penetrating keratoplasty eye if the donor trephine was 0.3 mm smaller in diameter than the recipient trephine. The axial length of individual keratoconus eyes is a major factor in determining postoperative refractive error. It therefore becomes important when considering variations in surgical procedures to reduce postoperative myopia.

Analysis of Variance↗
PubMed1992

Electrode comparison in pattern electroretinography.

In recent years, there has been great interest in recording the pattern electroretinogram (PERG) in glaucomatous and diabetic populations. The Dawson, Trick, and Litzkow thread electrode (DTLTE) and the gold foil electrode (GFE), commonly used for recording PERGs, were compared for variations in amplitude of response, test-retest variability, and patient comfort. Two study centers collected data on a total of 32 normal subjects. The subjects from the London center showed a slight (but not significant) preference for the DTLTE, and the Houston subjects also found the DTLTE to be significantly more comfortable (chi-square = 39, P less than 0.001). In both study groups, the GFE was found to produce a statistically larger amplitude of response than that obtained with the DTLTE. Significant differences were found regardless of the slow (transient, 3.1 Hz; F = 6.24; P = 0.0192) or fast (steady state, 8.3 Hz; F = 18.38; P = 0.0001) stimulus-presentation rate. Larger differences between the two electrodes occurred under steady-state conditions. Although there is no consensus as to the optimum recording conditions to obtain the subtle PERG, it appears the the GFE records larger responses than the DTLTE. However, test-retest data confirmed that the GFE records twice the amplitude of the DTLTE, and it also produced twice the variability (average percent difference over time for GFE, 15%; for DTLTE, 8%).

Adolescent↗
PubMed1991

Epikeratoplasty with nonlyophilized tissue in children with aphakia.

We studied 75 epikeratoplasty procedures using nonlyophilized tissue performed by eight ophthalmic surgeons in 70 eyes (47 patients) to correct for aphakia in children less than 8 years of age (mean age, 3.4 +/- 2.1 years). Of the 47 patients in the study, 24 were girls and 23 were boys; 23 patients had bilateral surgery. Seven of the epigrafts required removal; two were not replaced, and five underwent successful repeat epikeratoplasty. Overall, the success rate (that is, the percentage of epigrafts that remained optically and functionally clear throughout the course of this study) for the epikeratoplasty procedure was 89% (62 of 70 eyes) for initial surgery and 96% (67 of 70 eyes) for repeat surgery. The average spherical equivalent was +14.4 +/- 3.7 diopters preoperatively and +0.3 +/- 2.9 diopters one year after the operation. One year after the final surgical procedure, 42 of 56 eyes (75%) were within 3 diopters of emmetropia. In the 29 verbal patients, best-corrected visual acuity was 20/100 or better in 25 (86.2%) one year after the operation.

Aphakia↗
PubMed1991

A comparison of penetrating keratoplasty to epikeratoplasty in the surgical management of keratoconus.

Of 40 patients intolerant to contact lenses, 47 eyes with keratoconus were surgically corrected with either epikeratoplasty (N = 31) or penetrating keratoplasty (N = 16). The percentage of eyes in both groups that had visual acuity of 20/40 or better with contact lenses at one year were equal (14 of 15 eyes [93.3%] in the penetrating keratoplasty group; 27 of 29 eyes [93.1%] in the epikeratoplasty group); however, the penetrating keratoplasty procedure resulted in a higher percentage of eyes that had visual acuity of 20/20 than the epikeratoplasty group (11 of 15 eyes [73%] compared with seven of 29 eyes [24.1%], respectively). Both procedures resulted in significant corneal flattening, with the penetrating keratoplasty group producing an average of 3 diopters more keratometric reduction than the epikeratoplasty group one year postoperatively. Although no irreversible graft failures occurred, five of 16 eyes (31%) in the penetrating keratoplasty group had graft reactions. No serious complications were noted in the eyes of the epikeratoplasty group. Both procedures were effective in the surgical management of keratoconus.

Adolescent↗
PubMed1991

The relationship between skin maturation and electrical skin impedance.

When performing electrophysiological testing, high electrical impedance values are sometimes found in neonates. Since excessive impedance can invalidate test results, a study was conducted to delineate the relationship between skin maturation and electrical skin impedance. This study investigated the skin impedance in 72 infants ranging from 196 to 640 days of age from conception. Regression analyses demonstrated a significant relationship between impedance and age, with the highest impedance centered around full-term gestation with values falling precipitously at time points on either side. Clinically, impedance values fall to normal levels at approximately four months following full-term gestation. Skin impedance values are low in premature infants, but rapidly increase as the age approaches that of full-term neonates. Low impedance values in premature infants are attributed to greater skin hydration which results from immature skin conditions such as 1) thinner epidermal layers particularly at the transitional and cornified layers; 2) more blood flow to the skin; and 3) higher percentage of water composition. These factors facilitate the diffusion of water vapor through the skin. As the physical barrier to skin water loss matures with gestational age, the skin impedance reaches a maximum value at full term neonatal age. After this peak, a statistically significant inverse relationship exists between electrical skin impedance and age in the first year of life. This drop in skin impedance is attributed to an increase in skin hydration as a result of the greater functional maturity of eccrine sweat glands.

Age Factors↗
PubMed1990

The pattern electroretinogram in diabetes.

In 27 normal subjects and 64 insulin-dependent diabetic patients, we evaluated the pattern electroretinogram, which may reflect the neural activity of the spatially sensitive retinal ganglion cells. The amplitude of the pattern electroretinogram was reduced in diabetic patients who had no observable retinal changes. The amplitude was further reduced with increasing retinopathy. The pattern electroretinogram amplitude change was a more sensitive indicator of retinal change among the diabetic subpopulations than the statistically significant changes in latency. A significant correlation between pattern electroretinogram amplitude and the duration of diabetes were found in diabetic patients with either no observable retinopathy or minimal background retinopathy. The pattern electroretinogram may be useful as a quantitative, dependent variable to establish and monitor short-term metabolic and physiologic changes in diabetic patients.

Adolescent↗
PubMed1990

One year follow-up of epikeratoplasty for myopia.

Eighteen surgeons performed 166 consecutive epikeratoplasty procedures to correct myopia in 103 patients. Of this total, 147 (89%) were first surgeries and 19 (11%) were repeat surgeries. First surgery patients were divided into three subpopulations based on preoperative spherical equivalents (low -5.00 diopters [D] to -9.49 D, medium -9.50 D to -14.00 D, and high greater than -14.00 D). The percentage of eyes with 20/40 or better best corrected visual acuity before surgery was 93% for the low group, 89% for the medium group, and 57% for the high group. The percentage of eyes with 20/40 or better uncorrected visual acuity at 12 months after surgery was 58% for the low group, 42% for the medium group, and 17% for the high group. The average and median spherical equivalent after one year was -1.40 D (2.45 SD) and -1.00 D, respectively; 41% of the eyes were within one diopter of emmetropia, 65% within two diopters, and 76% within three diopters. Clinically significant regression was only noted in low and medium myope groups under 25 years of age. Repeat surgery outcomes were equivalent to those in first surgery patients who had a single procedure.

Adolescent↗
PubMed1990

Lacrimal tube repositioning: technique and ultrasonic assessment.

A section of migrated lacrimal silicone tubing was repositioned in a 7-year-old patient by dilating the lacrimal passage with hyaluronate solution and pushing the tube back into the nasal fossa with a probe. The position of the tube was postoperatively confirmed by ultrasonographic studies.

Child↗
PubMed1989

Effects of carbachol and acetylcholine on intraocular pressure after cataract extraction.

We compared the effect of carbachol and acetylcholine on intraocular pressure 24 hours after extracapsular cataract extraction. All agents were administered intracamerally at the time of surgery. Sixty patients scheduled for routine extracapsular cataract extraction and intraocular lens implantation were randomly assigned into one of three treatment groups: (1) carbachol, (2) acetylcholine, or (3) 0.5% balanced salt solution (placebo). Baseline intraocular pressures were determined the day before surgery, and postoperative pressures were measured approximately 24 hours after surgery. The group intraocular pressures averaged over preoperative and postoperative values were 21.06 mm Hg in the acetylcholine group, 19.36 mm Hg in the control group, and 17.30 mm Hg in the carbachol group. The average difference between preoperative and postoperative intraocular pressure measurements for the three groups were 7.33 mm Hg for the acetylcholine group, 8.73 mm Hg for the control group, and 2.20 mm Hg for the carbachol group. Only carbachol was significantly different from placebo on statistical subsequent testing. Carbachol is suggested as the agent of choice both for achieving intrasurgical miosis and prophylaxis of increasing intraocular pressure after cataract surgery.

Acetylcholine↗
PubMed1989

Glare testing in cataract patients: instrument evaluation and identification of sources of methodological error.

This study sought to determine the relative sensitivity of two commercially available glare testers in predicting outdoor acuity in a population of patients with minimal cataracts. Two target optotypes were evaluated: high contrast letters and varying contrast sinusoidal gratings. Although both instruments demonstrated a significant correlation between indoor and outdoor acuity, they showed a significant difference between predicted outdoor acuity and obtained visual acuity. The brightness acuity tester on high intensity was inaccurate in predicting outdoor vision regardless of test optotype, overpredicting glare disability in 76% (average) of the study population. Glare disability overpredictions fell to 8% on the medium setting with +/- 2 lines of vision classified as "no change." Using the same criterion, the Miller-Nadler glare tester overpredicted glare disability in 2% of the cataract population but underpredicted glare disability in 62%. In this study, letter optotypes resulted in less variability than sinusoidal grating stimuli. In addition, we identify several methodological factors to consider before designing a glare experiment. These potential sources of error can influence the outcome of any glare study that compares indoor and outdoor acuity and include the study population, visual stimuli (optotypes), and elements of the outdoor testing situation.

Adolescent↗
PubMed1989

The relationship between postnatal skin maturation and electrical skin impedance.

Electrical impedance, which is the resistance to an alternating current, is a parameter that is used to determine the condition of the electrode-skin interface before evoked potentials are recorded. High electrical impedance can result in inaccurate interpretation of evoked potentials due to excessive artifacts. This study investigated the electrical skin impedance in 36 full-term infants who ranged from 0 to 1 year of age to delineate the temporal relationship between skin maturation and skin impedance. Correlation and regression analyses demonstrated a statistically significant inverse relationship between electrical skin impedance and age during the first year of life. This drop in skin impedance during the first few postnatal months was attributed to an increase in skin hydration as a result of the greater functional maturity of eccrine sweat glands.

Aging↗