Biomedical subjects

Young H Kwon

Publications and source records attributed to Young H Kwon.

27 records · Page 2Linked to original sources

PubMed2003

Rate of optic disc cup progression in treated primary open-angle glaucoma.

PURPOSE: To quantitatively evaluate the rate of cup-to-disc ratio progression in treated patients with primary open-angle glaucoma and to identify clinical factors associated with cup progression. PATIENTS AND METHODS: Fifty one eyes of 51 treated primary open-angle glaucoma patients with a minimum of 9-year longitudinal series of stereoscopic optic disc photographs were studied. Eyes with any other ocular disease except for mild cataract were excluded. Each set of stereoscopic photographs was digitized and viewed stereoscopically on a computer screen using a hand-held stereoscope. Computer-aided planimetry was performed on each set of photographs with examiner-defined cup and disc margins using custom-made software. The software computed linear cup-to-disc ratios as well as peripapillary atrophy area. Both inter-observer and intra-observer reliabilities were evaluated in a masked, random fashion using intra-class correlation. Changes in linear cup-to-disc ratios and peripapillary atrophy were estimated using linear regression over time. All available clinical factors were evaluated for association with the rate of cup progression using a multiple regression model. RESULTS: All patients studied were Caucasian; 31(61%) were females. The mean age at the beginning of the study was 61.6 +/- 7.8 years (range 46-81). The mean follow-up period was 14.3 +/- 3.5 years (median 14.0, range 9.6-22.3). A total of 173 sets of stereo disc photographs were analyzed (3.4 +/- 1.3 per patient). The initial and final linear cup-to-disc ratios were 0.64 +/- 0.15 and 0.73 +/- 0.14 respectively. The inter-rater and intra-rater intraclass correlations were 0.76 (95% CI 0.61-0.87) and 0.97 (95% CI 0.93-0.98) respectively. Using linear regression the rate of linear cup-to-disc ratio change was 0.0068 +/- 0.0062 per year (range -0.0025- 0.0269). Three eyes had an increase in the peripapillary atrophy area. The higher yearly average intraocular pressure was significantly associated with faster rate of linear cup-to-disc ratios progression (P = 0.03). CONCLUSIONS: In treated patients with primary open-angle glaucoma, the rate of progressive optic disc cupping was slow (LCDR progression of 0.0068 per year). The higher yearly average intraocular pressure was significantly associated with a faster rate of cup progression.

Aged↗

PubMed2003

Functional characterization of retina and optic nerve after acute ocular ischemia in rats.

PURPOSE: To functionally characterize the status of the rat retina and optic nerve after acute elevation of intraocular pressure (IOP) and to determine the dynamics of the pathologic changes in the ischemic retina and optic nerve. METHODS: Retinal ischemia was induced in rats by acutely increasing the IOP (110 mm Hg/60 minutes). Direct and indirect pupil light reflexes (PLRs) were recorded from the noninjured eye, and electroretinograms (flash and flicker ERG) were recorded from the injured and control eyes before and after surgery. Amplitudes and latencies were calculated for each recording session. RESULTS: Preoperative PLR(ratio)s (indirect/direct PLR) were 76.7 +/- 2.6 (mean +/- SEM). Twenty-four hours after surgery the PLR(ratio) was 15.2 +/- 12.8, 10 days after surgery, 11.6 +/- 9.8; 20 days after surgery, 26.5 +/- 8.0; and 28 days after surgery, 33.27 +/- 9.3. However, at day 35, the PLR had significantly recovered (41.1 +/- 7.3) when compared with the 24-hour postoperative ratios (P < 0.01, repeated-measures ANOVA). Forty-two days after surgery, the PLR(ratio) started to decrease once again in the injured eyes (28.7 +/- 5.9). Electroretinographic amplitudes (full-field flash ERG) followed a similar pattern. Cone responses (flicker ERG) were measured 42 days after surgery and revealed defects in injured eyes (control eyes: 46.6 +/- 2.9 microV, injured eyes: 3.4 +/- 1.7 microV). Histologic analysis revealed ischemic damage to all retinal layers, with the primary defects localized to the central retina. CONCLUSIONS: Acute ocular ischemia causes a significant decrease in retinal function, as measured by PLR and ERG, although over time the rat retina and optic nerve show partial regain of function.

Acute Disease↗

PubMed2003

Laser-induced mouse model of chronic ocular hypertension.

PURPOSE: To develop an inducible mouse model of glaucoma. METHODS: An obstruction of aqueous humor outflow in adult C57BL6/J mice was induced by combined injection of indocyanine green (ICG) dye into the anterior chamber and diode laser treatment. To evaluate intraocular pressure (IOP), tonometry was performed with a modified Goldmann tonometer. The function of the retina was evaluated with electroretinography (ERG). RESULTS: IOP was significantly elevated in surgical eyes compared with control eyes: before surgery, 15.2 +/- 0.6 mm Hg; 10 days after surgery, 33.6 +/- 1.5 mm Hg (P < 0.001); and 30 days after surgery, 27.4 +/- 1.2 mm Hg (P < 0.001). However, 60 days after surgery, IOP in the surgical eyes decreased to 19.5 +/- 0.9 mm Hg and was not significantly different compared with control eyes (control, 17.3 +/- 0.7 mm Hg; P = 0.053). ERG amplitudes, expressed as a ratio (surgical/control), were decreased in surgical eyes. The amplitudes for b-wave were: before surgery, 107.6% +/- 4.6%; 28 days after surgery, 61% +/- 4% (P < 0.001); and 56 days after surgery, 62% +/- 5.6% (P < 0.001). Oscillatory potentials were the most dramatically affected: before surgery, 108.6% +/- 6.7%; 28 days after surgery, 57.5% +/- 5% (P < 0.01); and 56 days after surgery, 57% +/- 8.5% (P < 0.001). Amplitudes of the a-waves had relatively smaller but still significant deficits: before surgery, 105.8% +/- 6.9%; 28 days after surgery, 72.2% +/- 5.4% (P < 0.01); and 56 days after surgery, 79.8% +/- 11.0% (P < 0.01). Histologic analysis of the surgical eyes revealed development of anterior synechia, loss of retinal ganglion cells (RGCs), and thinning of all retinal layers. Electron microscopy of optic nerve cross sections revealed swelling and degeneration of the large diameter axons and gliosis. CONCLUSIONS: Diode laser treatment of ICG saturated episcleral veins causes a chronic elevation of IOP and sustained ERG deficits.

Animals↗

PubMed2002

Variations in the myocilin gene in patients with open-angle glaucoma.

OBJECTIVE: To determine the prevalence and associated phenotype of myocilin (MYOC) coding sequence variations and a specific promoter polymorphism (MYOC.mt1) in patients with glaucoma and glaucoma suspects. METHODS: A consecutive, unselected series of 779 patients (652 with open-angle glaucoma and 127 glaucoma suspects) were recruited from a university medical center and clinically characterized. The coding sequences of the MYOC gene and the MYOC.mt1 locus in the promoter region were screened for sequence variations. We determined the prevalence of MYOC coding sequence mutations and the MYOC.mt1 promoter polymorphism. We also compared the clinical features of individuals with and without mutations and the MYOC.mt1 promoter polymorphism. RESULTS: Plausible disease-causing sequence variations (DCVs) in the MYOC gene were found in 3.0% of the entire group. Such variations were found in patients with most forms of open-angle glaucoma studied. Patients with primary open-angle glaucoma (POAG) who harbored coding sequence DCVs were clinically similar to patients without them. Patients who harbored the rarer allele of the MYOC.mt1 promoter polymorphism were no different in any measure of disease severity from those who harbored the more common allele. CONCLUSIONS: MYOC DCVs were found in approximately 3% of patients with glaucoma and glaucoma suspects. The 2 alleles of the MYOC.mt1 promoter polymorphism were equally distributed among patients with POAG and healthy control subjects. Patients with POAG who harbored the rarer allele of the MYOC.mt1 promoter polymorphism were no different from those with the more common variant in any measure of disease severity. CLINICAL RELEVANCE: Testing for the MYOC.mt1 promoter polymorphism appears to be of no value in the evaluation of patients with glaucoma.

Adult↗

PubMed2002

Progressive axial myopia in a juvenile patient with traumatic glaucoma.

PURPOSE: To report a case of progressive axial myopia associated with traumatic glaucoma in a juvenile patient with no systemic disease. DESIGN: Interventional case report. METHODS: In a 15-year-old male, serial ocular examinations, including manifest refraction, tonometry, and axial eye length measurement, were performed over a 6-year period, beginning with blunt trauma, right eye, followed by a series of surgical procedures for traumatic cataract and glaucoma. RESULTS: A 4-diopter myopic shift (from -1.25 to -5.25) with a 1.5 mm increase in the axial eye length occurred, whereas the intraocular pressure increased from 21 to 46 mm Hg, during a 2-year period. The refraction, axial eye length, and intraocular pressure remained stable during the same period in the fellow, normal eye. CONCLUSION: Progressive axial myopia associated with traumatic glaucoma is possible in a juvenile patient in his late teens.

Adolescent↗

PubMed2002

A case-control comparison of the clinical characteristics of glaucoma and ocular hypertensive patients with and without the myocilin Gln368Stop mutation.

PURPOSE: To determine whether primary open-angle glaucoma (POAG) and ocular hypertensive (OHT) patients who harbor the myocilin Gln368Stop mutation differ in phenotype or clinical course from patients without the mutation. DESIGN: Case-control study. METHODS: A retrospective case-control study compared all known POAG patients (n = 18) and OHT patients (n = 4) harboring the Gln368Stop mutation evaluated by the University of Iowa Glaucoma Service with control patients from the same population. Patients and control subjects were matched for diagnosis, age, sex, and race and were compared for phenotype and clinical course. RESULTS: Mean age of disease onset and mean peak intraocular pressures (IOPs) of cases were similar to those reported by other studies. There was no statistically significant difference between cases and controls for the following variables: age at onset, peak intraocular pressure, Snellen visual acuity, number of medications, Humphrey visual field (HVF) mean deviation, HVF pattern deviation, number of filtering surgeries performed, time intervals from diagnosis to argon laser trabeculoplasty (ALT), diagnosis to first filtering surgery, ALT to first filtering surgery, and percent change in IOP after ALT and after first filtering surgery. CONCLUSIONS: There is no statistically significant difference between the onset and clinical course of POAG and OHT caused by the Gln368Stop mutation and POAG and OHT not associated with the mutation.

Adult↗

PubMed2002

Rate and pattern of visual field decline in primary open-angle glaucoma.

PURPOSE: To study the rate and pattern of visual field decline in primary open-angle glaucoma. DESIGN: Retrospective observational case series. PARTICIPANTS: Forty eyes of 40 patients with primary open-angle glaucoma that were followed longitudinally with serial Goldmann visual fields for a minimum period of 8 years in an academic institution. Eyes with any other ocular disease except for mild cataract were excluded. METHODS: Visual fields obtained with worse than 20/50 Snellen visual acuity from cataract were excluded from analysis. In the remainder (671 Goldmann visual fields), the I4e isopter was quantified manually using a grid template previously described by Esterman. The visual field was divided into central and peripheral, superior and inferior, and nasal and temporal regions, all centered at the blind spot. The rate of visual field decline was estimated for each visual field region (including the four quadrants: superonasal [SN], superotemporal [ST], inferotemporal [IT], and inferonasal [IN]) using linear regression. Asymmetry of visual field progression was determined by comparing the rates of progression among the four quadrants. Pertinent clinical factors were evaluated for association with the asymmetry of visual field progression. MAIN OUTCOME MEASURES: Rates of visual field decline for the entire visual field and each region. Long-term clinical outcome measures, including visual acuity, cataract and cup-to-disc ratio progression, intraocular pressures, and medical and surgical interventions were also studied. RESULTS: The rate of visual field change was -1.3% per year for the entire visual field. The rates of visual field section change (in % per year) were -1.3 (central), -1.4 (peripheral), -1.5 (superior), -1.2 (inferior), -1.4 (nasal), -1.2 (temporal), -1.8 (SN), -1.3 (IT), -1.2 (IN), and -1.1 (ST). About half the patients showed symmetric visual field decline, whereas others showed a more asymmetric pattern. Asymmetric visual field progression was associated with the presence of disc hemorrhage, overall rate of visual field progression, and surgical intervention for glaucoma. CONCLUSIONS: In this group of selected patients with primary open-angle glaucoma with a long-term follow-up, all sections of the visual field declined over time. Disc hemorrhage was associated with more asymmetric visual field progression, implicating focal damage to the optic disc.

Adult↗

PubMed2002

Characterization of the pupil light reflex, electroretinogram and tonometric parameters in healthy rat eyes.

PURPOSE: To characterize the pupil light reflex (PLR), electroretinographic (ERG) and tonometric parameters in healthy rat eyes. METHODS: Brown Norway rats were used for experiments. The PLR was evaluated with a computerized pupillometer (n = 27), ERGs were recorded simultaneously from both eyes (n = 27) and IOP was measured with a Tonopen (n = 15). RESULTS: The analysis of the PLR parameters confirmed that the consensual PLR had a significantly smaller amplitude (0.1-0.2 mm; p = 0.03) and an increased latency time (p = 0.001) compared to the direct PLR. Electroretinography revealed an a-wave amplitude of 207.2 +/- 13 microV with a latency of 25.6 +/- 0.7 ms, and a b-wave 554.3 +/- 24.5 microV with a latency of 21.4 + 1.8 ms. The flicker ERG recording revealed amplitudes of 40.6 +/- 2.4 microV. Tonometry measurements revealed that isoflurane, but not halothane, anesthesia suppressed the IOP (non-anesthetized: 25.3 +/- 1.0 mmHg; 1% halothane + 30% NO: 26.2 +/- 1.1 (p > 0.1); 1% isoflurane + 30% NO: 20.1 + 1.6 (p < 0.05)). CONCLUSIONS: Consensual PLR in rats has a relative deficit compared to the direct PLR. Isoflurane anesthesia has a suppressive effect on the IOP in healthy rat eyes.

Anesthetics, Inhalation↗

PubMed2002

Digital stereo image analyzer for generating automated 3-D measures of optic disc deformation in glaucoma.

The major limitations of precise evaluation of retinal structures in present clinical situations are the lack of standardization, the inherent subjectivity involved in the interpretation of retinal images, and intra- as well as interobserver variability. While evaluating optic disc deformation in glaucoma, these limitations could be overcome by using advanced digital image analysis techniques to generate precise metrics from stereo optic disc image pairs. A digital stereovision system for visualizing the topography of the optic nerve head from stereo optic disc images is presented. We have developed an algorithm, combining power cepstrum and zero-mean-normalized cross correlation techniques, which extracts depth information using coarse-to-fine disparity between corresponding windows in a stereo pair. The gray level encoded sparse disparity matrix is subjected to a cubic B-spline operation to generate smooth representations of the optic cup/disc surfaces and new three-dimensional (3-D) metrics from isodisparity contours. Despite the challenges involved in 3-D surface recovery, the robustness of our algorithm in finding disparities within the constraints used has been validated using stereo pairs with known disparities. In a preliminary longitudinal study of glaucoma patients, a strong correlation is found between the computer-generated quantitative cup/disc volume metrics and manual metrics commonly used in a clinic. The computer generated new metrics, however, eliminate the subjective variability and greatly reduce the time and cost involved in manual metric generation in follow-up studies of glaucoma.

Algorithms↗