PubMed Health⌕ Search

Biomedical subjects

N T Choplin

Publications and source records attributed to N T Choplin.

13 recordsLinked to original sources
PubMed2001

The sensitivity and specificity of scanning laser polarimetry in the detection of glaucoma in a clinical setting.

OBJECTIVE: A study was conducted to determine the sensitivity and specificity of masked experts in classifying results obtained from normal eyes, glaucomatous eyes, and eyes suspicious for glaucoma using the Nerve Fiber Analyzer GDx (Laser Diagnostic Technologies, San Diego, CA), a scanning polarimeter. DESIGN: Retrospective consecutive case series. METHODS: Consecutive subjects seen in a glaucoma clinic were imaged with the GDX: The masked printouts were distributed to nine experienced users of the machine, who were asked to classify the scan from each eye as normal, suspicious for glaucoma, or consistent with glaucoma. No specific guidelines for interpretation were used. The interpretations were compared with the known diagnoses obtained from review of the subjects' medical records. The number of correct diagnoses, false-positive answers (specificity), and false-negative answers (sensitivity) were noted for each observer and averaged for all nine. Interobserver agreement was calculated by use of the kappa statistic. MAIN OUTCOME MEASURES: False-positive and false-negative responses from reviewers' assessments compared with known diagnoses from chart review. RESULTS: A total of 104 eyes was included: 29 normal eyes, 33 eyes from glaucoma suspects, and 42 eyes with glaucoma. Interobserver agreement was moderate for normals (kappa = 0.42, P = 0.00) and glaucoma (kappa = 0.48, P = 0.00), but slight for glaucoma suspects (kappa = 0.09, P = 0.00). Overall, the average sensitivity was 74% and the specificity was 74%. If only considering whether or not the scan represented glaucoma (i.e., reviewer assessment of "suspect" meant "not glaucoma"), the average sensitivity was 86% and the specificity 83%. If only considering whether a scan was normal or not (i.e., reviewer assessment of "suspect" meant "abnormal"), the sensitivity was 83% and the specificity 86%. Eliminating glaucoma suspects (but allowing the assessment of "suspect") increased overall sensitivity to 80% and specificity to 79%. With suspects eliminated, sensitivity was 80% and specificity 91% for determination of glaucoma, and sensitivity was 93% and specificity 79% for determination of abnormality. CONCLUSIONS: Scanning laser polarimetry may have good sensitivity and specificity for separating normal from abnormal eyes, but it is not as good for classifying unknown subjects when glaucoma suspects are included. Evaluation of new parameters and continued clinical experience may help develop guidelines for interpretation and/or specific indicators for glaucomatous damage to increase the sensitivity and specificity.

Diagnostic Techniques, Ophthalmological↗
PubMed1999

The effect of excimer laser photorefractive keratectomy for myopia on nerve fiber layer thickness measurements as determined by scanning laser polarimetry.

OBJECTIVE: Scanning laser polarimetry measures the retardation of polarized laser light as it passes through the birefringent retinal nerve fiber layer (RNFL). Because retardation is directly proportional to the number of retinal nerve fibers, indirect measurements of the RNFL thickness are obtained. A fixed compensatory mechanism is used to correct for retardation attributed to birefringence in the cornea and anterior segment. Excimer laser photorefractive keratectomy (PRK) corrects myopia by ablating tissue from the cornea. This study was conducted to determine the effect of this ablation on RNFL measurements. DESIGN: Prospective comparative case series. PARTICIPANTS: Eighteen patients. METHODS: Patients undergoing PRK had RNFL measurements performed with the GDx Nerve Fiber Analyzer (Laser Diagnostic Technologies, San Diego, CA), a scanning laser polarimeter, in both eyes before and 90 days after PRK in the first eye. MAIN OUTCOME MEASURES: Fourteen different GDx parameters were analyzed for statistically significant differences preoperatively and 3 months postoperatively in the treated and untreated eye using Hotelling's T-squared generalized means test. RESULTS: Eighteen patients underwent PRK in the nondominant eye first. Preoperative refractions averaged -3.8+/-1.6 diopters (D), with an average correction of 3.4+/-1.9 D, corresponding to 49.7+/-20.5 microns of ablation. There were no statistically significant preoperative differences between the fellow eyes in refractive error (P = 0.65). Postoperatively, there were no statistically significant changes in any GDx parameter in the treated eye compared with the untreated control eye (P = 0.21). CONCLUSIONS: Excimer laser PRK for moderate myopia has no significant effect on RNFL thickness measurements as determined by scanning laser polarimetry.

Adult↗
PubMed1998

Differentiating patients with glaucoma from glaucoma suspects and normal subjects by nerve fiber layer assessment with scanning laser polarimetry.

PURPOSE: A study was conducted to determine normative data for nerve fiber layer measurements as obtained by scanning laser polarimetry with the Laser Diagnostic Technologies Nerve Fiber Analyzer II, identify factors affecting the measurements, and identify parameters capable of differentiating normal subjects from patients with glaucoma and patients suspected of having glaucoma because of ocular hypertension or because of a large cup-to-disc ratio (GS-disc). DESIGN: A case series. PARTICIPANTS: Four hundred normal subjects, 35 patients with ocular hypertension, 42 patients with glaucoma, and 17 glaucoma suspects based on optic disc appearance participated. METHODS: Nerve fiber layer thickness assessments were determined in normal subjects (with normal-appearing optic nerves and normal visual fields). The results were compared to measurements from samples of age-matched patients with ocular hypertension (with normal visual fields), patients suspected of having glaucoma based on enlarged cup-to-disc ratios, and patients with open-angle glaucoma who had visual field loss. RESULTS: The majority of the parameters derived from the measurements showed no significant relationship to age, although some parameters tended to decrease with increasing age. Multiple parameters showed statistically significant differences between normal subjects and patients with glaucoma. In particular, the intraellipse sector variability, an indirect measure of the shape of the nerve fiber layer in an ellipse surrounding the nerve head, showed statistically significant differences between normal subjects and patients with glaucoma as well as between glaucoma suspects and normal subjects. Similar results were seen with the superior maxima, the average thickness assessment value of the 1500 thickest points in the superior bundle. CONCLUSIONS: Assessments of nerve fiber layer thickness as determined by scanning laser polarimetry can differentiate patients with glaucoma from normal subjects and may identify otherwise undetected damage in glaucoma suspects.

Diagnostic Techniques, Ophthalmological↗
PubMed1997

A 1-year study of brimonidine twice daily in glaucoma and ocular hypertension. A controlled, randomized, multicenter clinical trial. Chronic Brimonidine Study Group.

OBJECTIVE: Brimonidin tartrate is a highly selective alpha 2-agonist. This study investigates the safety and efficacy of 0.2% brimonidine administered twice daily for 1 year in patients with glaucoma or ocular hypertension. METHODS: The study design was a multicenter, double-masked, randomized, parallel-group, active-controlled comparison clinical trial. Subjects instilled 0.2% brimonidine or 0.5% timolol maleate twice daily for 12 months. Subjects were examined at baseline, week 1, and months 1, 2, 3, 6, 9, and 12. A subset of subjects was examined at week 2. RESULTS: Of 443 subjects enrolled in this study, 374 met the entry criteria; 186 received brimonidine and 188 received timolol. Brimonidine-treated subjects showed an overall mean peak reduction in intraocular pressure (IOP) of 6.5 mm Hg; timolol-treated subjects had a mean peak reduction in IOP of 6.1 mm Hg. Brimonidine lowered mean peak IOP significantly more than timolol at week 2 and month 3 (P < .03); no significant difference was observed between the groups for this variable at other visits throughout the 1-year course of the study. No evidence of tachyphylaxis was seen in either group. Allergy was seen in 9% of subjects treated with brimonidine. Dry mouth was more common in the brimonidine-treated group than in the timolol-treated group (33.0% vs 19.4%), but complaints of burning and stinging were more common in the timolol-treated group (41.9%) than in the brimonidine-treated patients (28.1%). Headache, fatigue, and drowsiness were similar in the 2 groups. In general, the tolerance to medication was acceptable. CONCLUSIONS: Brimonidine is safe and effective in lowering IOP in glaucomatous eyes. Brimonidine provides a sustained long-term ocular hypotensive effect, is well tolerated, and has a low rate of allergic response.

Administration, Topical↗
PubMed1992

Surgically-induced astigmatism in combined ECCE with filtering procedures compared to ECCE alone.

Extracapsular cataract extraction with implantation of a posterior chamber lens combined with filtering surgery (glaucoma triple procedure) is frequently employed in the co-management of cataract and glaucoma. Nineteen triple procedures with a minimum of six months follow up were compared to 19 cases of extracapsular cataract extraction with lens implant matched for age, sex, and surgeon with regard to surgically induced astigmatism as determined by vector analysis. Follow up averaged 10 months for the triple group and 14 months for the controls. There was no statistically significant difference in preoperative astigmatism between the two groups nor in the mean number of sutures cut. Postoperatively, the keratometric cylinder averaged 2.55 +/- 1.54 diopters for the cases and 1.20 +/- 1.11 D for the controls; the difference of 1.36 D was statistically significant (P = .004). The postoperative refractive cylinder was 2.34 +/- 1.54 D for the cases and 1.29 +/- 1.07 D for the controls; the difference of 1.05 D was statistically significant (P = .017). With regard to surgically-induced astigmatism, vector analysis showed that the cases averaged 2.18 +/- 1.25 D and the controls 1.23 +/- 0.81 D; the difference of 0.95 D was statistically significant (P = .006). With regard to surgically-induced astigmatism, vector analysis showed that the cases averaged 2.18 +/- 1.25 D and the controls 1.23 +/- 0.81 D; the difference of 0.95 D was statistically significant (P = .006). When analyzed for change along the vertical meridian, the cases averaged 1.12 +/- 1.57 D surgically-induced against-the-rule astigmatism, as compared with 0.30 +/- 1.16 D for the controls (difference, 0.83 D; P = .062). The glaucoma triple procedures induced approximately 1.00 D more cylinder than the controls.

Aged↗
PubMed1992

Glaucoma screening in primary care: the role of noncontact tonometry.

BACKGROUND: Guidelines for glaucoma screening by the primary care physician have not been firmly established. Despite its limitations as a screening test, intraocular pressure measurement by tonometry remains the mainstay of glaucoma monitoring but is not widely used in the primary care setting. The purpose of this study was to compare the effectiveness of noncontact tonometry using the Pulsair instrument with that of conventional tonometry using the Goldmann applanation tonometer as a screening tool for glaucoma. METHODS: Intraocular pressure was measured by non-contact and Goldmann applanation tonometry in both eyes of 50 volunteers who enrolled in a glaucoma screening program at a primary care clinic. RESULTS: Noncontact tonometry correctly identified over 90% of the patients with intraocular pressures greater than 22 mm Hg. CONCLUSIONS: Noncontact tonometry is an easy, practical, and well-tolerated method of intraocular pressure measurement. When combined with direct ophthalmoscopy, noncontact tonometry can easily be used in routine primary care health examinations to detect glaucoma.

Adult↗
PubMed1990

The effect of stimulus size on the measured threshold values in automated perimetry.

Patients with severely depressed visual fields as determined by automated static perimetry are often tested with larger test stimuli in order to obtain meaningful data. "Normal" threshold values are known and included in some perimeters' data analysis programs for stimulus III, but not for larger stimuli. Using a user-defined program on the Octopus 201 perimeter to determine mean retinal sensitivity, a study was conducted in 17 normal subjects to determine the effect of stimulus size on measured threshold. With stimulus III, the mean retinal sensitivity within the central 30 degrees was 28.4 +/- 2.3 dB; it was 31.9 +/- 2.3 dB for stimulus IV, and measured 36.00 +/- 2.5 dB with stimulus V. The differences between the values are statistically significant (P less than 0.001). It is not known whether these differences can be generalized from normals to patients with glaucoma or other diseases.

Adult↗
PubMed1984

Radial keratotomy.

Explore the source record for details and available documents.

Contact Lenses, Hydrophilic↗
PubMed1980

Bullous keratopathy accompanying essential iris atrophy: response to lowered intraocular pressure.

We present a patient with essential iris atrophy who was normotensive and yet had corneal edema and bullous keratopathy which cleared upon lowering the intraocular pressure. It is proposed that in this patient the endothelial functional status was so compromised that it could not handle the amount of fluid driven into the cornea by a normal intraocular pressure. A more favorable balance between intraocular pressure and endothelial functional status was obtained by lowering the intraocular pressure with acetazolamide and timolol.

Acetazolamide↗