Biomedical subjects

L C Woung

Publications and source records attributed to L C Woung.

11 recordsLinked to original sources

PubMed2001

Change in the area of laser posterior capsulotomy: 3 month follow-up.

PURPOSE: To monitor the change in the area of laser posterior capsulotomy over time to determine whether and when the area becomes stable. SETTING: Taipei Municipal Yang-Ming Hospital, Taipei, Taiwan, Republic of China. METHODS: This prospective study comprised 53 eyes (46 patients) with posterior capsule opacification (PCO) that had neodymium:YAG (Nd:YAG) laser posterior capsulotomy. The capsulotomy area was measured 30 minutes, 1 week, and 1 and 3 months postoperatively. The correlations between the capsulotomy area and changes in other measurements were also evaluated. RESULTS: The capsulotomy area increased significantly 1 month after laser treatment and stabilized thereafter. The mean area increased from 9.26 mm(2) +/- 0.47 (SEM) to 10.88 +/- 0.66 mm(2) (17.49%) after 3 months. At 3 months, the area was 19.10% +/- 4.85% larger than at 30 minutes after capsulotomy. The change in area did not correlate significantly with changes in intraocular pressure, anterior chamber depth, spherical equivalent, refractive astigmatism, keratometric astigmatism, or residual astigmatism from 1 week after treatment. CONCLUSION: The capsulotomies enlarged progressively up to 1 month after Nd:YAG laser posterior capsulotomy for PCO and stabilized thereafter.

Aged↗

PubMed2000

Influence of laser posterior capsulotomy on anterior chamber depth, refraction, and intraocular pressure.

PURPOSE: To evaluate the effect of neodymium:YAG (Nd:YAG) laser posterior capsulotomy on anterior chamber depth (ACD), intraocular pressure (IOP), and refraction, including spherical equivalent (SE) and various forms of astigmatism. SETTING: Taipei Municipal Yang-Ming Hospital, Taipei, Taiwan. METHODS: Fifty-three eyes of 46 patients with posterior capsule opacification were included in this prospective study. An Nd:YAG laser was used to perform posterior capsulotomy. Patients' ACD, IOP, and refraction were measured before the capsulotomy and 30 minutes, 1 week, and 1 and 3 months after. RESULTS: There were no statistically significant differences in ACD, IOP, or SE (P =.201, P =.465, and P =.109, respectively). However, there were significant decreases in the magnitudes of refractive astigmatism and residual astigmatism after laser treatment (P =.012 and P <.001, respectively). CONCLUSIONS: Although an Nd:YAG laser posterior capsulotomy did not significantly change ACD, IOP, or SE, it decreased the magnitudes of refractive astigmatism and residual astigmatism 1 week postoperatively. These stabilized thereafter.

Aged↗

PubMed2000

Digital retroilluminated photography to analyze posterior capsule opacification in eyes with intraocular lenses.

PURPOSE: To compare the formation and rates of posterior capsule opacification (PCO) in eyes with poly(methyl methacrylate) (PMMA) versus silicone intraocular lenses (IOLs) using an in vivo objective method. SETTING: Taipei Municipal Yang-Ming Hospital, Taipei, Taiwan, Republic of China. METHODS: This prospective study comprised 40 eyes with senile cataract receiving phacoemulsification with capsular implantation of an IOL from March to April 1997. The uneventful surgeries were performed using the stop and chop method by the same surgeon. Twenty eyes received a PMMA IOL (Pharmacia 812A) and 20, a silicone IOL (AMO SI-30NB). One year later, digital retroillumination images taken with the EAS-1000 anterior segment analysis system (Nidek) were used to analyze posterior capsule transparency over the central 3.0 and 5.0 mm optic zones and evaluate the degree of PCO over the central and peripheral zones. RESULTS: Over the central 5.0 mm optic zone, mean transparency of the capsule was 87.71% +/- 11.35% (SD) in the silicone group and 79.22% +/- 21.10% in the PMMA group (P = .17). Over the central 3.0 mm optic zone, the means were 97.17% +/- 5.96% and 86.32% +/- 19.60%, respectively (P = .048). Mean opacity in the central zone was 75.18 +/- 13.22 digital opacity units (OUs) in the silicone group and 80.24 +/- 7.93 OUs in the PMMA group (P = .18). The means in the peripheral zone were 88.49 +/- 18.47 OUs and 90.35 +/- 9.98 OUs, respectively (P = .71). CONCLUSION: The posterior capsule in the silicone IOL group was more transparent than in the PMMA IOL group over the central 3.0 mm optic zone after 1 year follow-up.

Aged↗

PubMed2000

Modulation transfer function and critical flicker frequency in high-myopia patients.

BACKGROUND AND PURPOSE: Critical flicker frequency (CFF) decreases due to optic nerve and retinal damage in patients with optic neuritis or glaucoma. Because retinal degeneration is also found in high myopia, we investigated whether the modulation transfer function (MTF) and CFF are altered in patients with high myopia. METHODS: Forty-six patients with high myopia (< -8 diopters, D) were recruited from our outpatient department. The control group comprised 21 young volunteers with myopia of 0 to -2 D. The myopic and control groups were similar in terms of age and sex. RESULTS: At all frequencies tested, the myopic group had lower CFF and higher modulation values than the control group. The mean CFF was significantly lower in myopic patients (46.8 +/- 9.0 Hz) than in control subjects (52.5 +/- 4.4 Hz). Patients with extremely high myopia (< -10 D) had significantly greater modulation values at 5, 10, 15, 55 and 60 Hz than those with moderately high myopia (-8 D to -10 D). The CFF did not differ significantly between those with extremely high (46.3 +/- 8.8 Hz) and those with moderately high (49.0 +/- 6.9 Hz) myopia. CONCLUSIONS: The findings of this study support that the CFF decreases and MTF increases in patients with high myopia, and that the alternation of MTF is related to the degree of myopia. CFF and MTF may, therefore, have potential as indexes to evaluate the severity of retinal degeneration in patients with high myopia.

Adolescent↗

PubMed2000

Ptosis surgery on chronic myasthenia gravis.

We report three cases of long-standing, early onset myasthenia gravis. The eyes of all three patients eventually became disabled, and the patients were almost unable to move their eyes in any direction. We termed this condition as "frozen eyes" appearance. We discuss the unique clinical condition and follow the electromyographic and neuro-ophthalmological characteristics. The patients all suffered from ptosis, mild to moderate exotropia, and facial and oropharyngeal weakness. All of the patients responded to the neostigmine test positively at the early stage. Two of them were seropositive. The results of electromyography for two of these three cases were abnormal. The average duration of follow-up was 5 years. The treatments included conventional recession and resection procedures with adjustable sutures for strabismus and frontalis suspension for blepharoptosis. The patients achieved stable satisfactory results in over one-and-a-half years of postoperative follow up.

Adult↗

PubMed2000

Scanning laser polarimetry in evaluation of retinal nerve fiber layer thickness for normal Taiwanese.

Scanning laser polarimetry has been used recently for the measurement of retinal nerve fiber layer (RNFL) thickness, taking advantage of the birefrigence of the RNFL. We observe the RNFL with the instrument and try to find out a set of normal basic values of the RNFL thickness for clinical comparison. One hundred normal volunteers of different age groups were recruited for this study. There are 44 males and 56 females with a mean (1SD) age of 36.17(14.77) years. Three consecutive 15-degree polarimetric maps were acquired for each subject. RNFL thickness measurements were obtained at 1.75 disc diameters ring from the optic nerve. Four 90-degree quadrants were identified. As a result, the average of RNFL thickness is 90.69 (20.20) microns in the superior quadrant, 80.45 (17.4) microns in the inferior quadrant, 59.28 (15.37) microns in the nasal quadrant, and 48.98 (15.72) microns in the temporal quadrant with a mean thickness value of 69.86 (13.97) microns. Superior and inferior quadrants showed a comparatively thicker nerve fiber layer than nasal and temporal quadrants. The temporal quadrant was always the lowest. The axial length does not affect the RNFL thickness and no significant difference between males and females exists. However, an obvious inverse linear correlation between age and the RNFL thickness in all quadrants is found. The average RNFL thickness decreased with age by 0.26 micron per year. (R2 = 0.081, p-value = 0.004). When compared with the normal range, age-match would be necessary.

Adolescent↗

PubMed1998

Position of poly(methyl methacrylate) and silicone intraocular lenses after phacoemulsification.

PURPOSE: To compare the positional change of poly(methyl methacrylate) (PMMA) and silicone intraocular lenses (IOLs) in vivo after phacoemulsification. SETTING: Taipei Municipal Yang-Ming Hospital, Taipei, Taiwan. METHODS: A prospective study of 70 cataractous eyes treated by phacoemulsification with IOL implantation was carried out. The eyes were randomized into 2 groups based on IOL type: 1-piece PMMA IOL; 3-piece silicone IOL. The amount of IOL tilt and decentration was measured and anterior chamber depth (ACD) determined by Scheimpflug photography using an anterior eye segment analysis system (EAS-1000, Nidek). All eyes were examined 1 week and 1 to 6 months after surgery. RESULTS: No statistically significantly differences were found in the amount of tilt and decentration between 2 IOL types throughout the study. The ACDs were relatively constant in both groups through the early postoperative periods. CONCLUSION: The stability of PMMA and silicone IOLs were the same after phacoemulsification.

Aged↗

PubMed1998

Accommodation and pupillary response in early-onset myopia among schoolchildren.

PURPOSE: To investigate changes in accommodation and pupillary reaction in early-onset myopia among children. METHODS: An objective infrared optometer and a pupillometer were used to evaluate simultaneously tonic accommodation, accommodative response, accommodative adaptation, and pupil diameter in 19 schoolchildren with early-onset myopia and 15 age-matched emmetropic controls. RESULTS: Tonic accommodation in the early-onset myopes (1.03 D) was significantly less than in the emmetropes (1.37 D) (p < 0.05), whereas accommodative response and accommodative adaptation showed no significant difference between the early-onset myopes and emmetropes. The average pupil diameter after 20 min of dark adaptation in the early-onset myopes was 4.52 mm, which was significantly smaller than that in the emmetropes (5.21 mm) (p < 0.05). During nearwork stimulation, the average pupil diameter further decreased to 3.83 mm in the early-onset myopes and 4.78 mm in the emmetropes (p = 0.003). CONCLUSION: These results suggest that low tonic accommodation and small pupil diameter may play important roles in the pathogenesis of early-onset myopia among schoolchildren.

Accommodation, Ocular↗

PubMed1995

Visual function in recovered ethambutol optic neuropathy.

The visual acuity of the patient with ethambutol optic neuropathy will recover within 3 to 4 months after discontinuing the drug. We studied the extent of the recovery of other visual functions. Thirty-six axial type ethambutol optic neuropathy patients, who visited our neuro-ophthalmology clinic from January, 1990, to December, 1993, were included in this study. Fifteen patients (29 eyes) regained their visual acuity to better than 1.0. The average follow-up period following the recovery is 21.7 months. Pattern reversal VEP, Farnsworth-Munsell 100-Hue color vision test, critical flicker frequency (CFF), visual field perimetry, contrast sensitivity and edge-light pupil cycle time were assessed for every affected eye. Latency (P100) of visually evoked potential was delayed in 34.5% (10/29) of eyes. In color vision, 48.3% (14/29) of eyes had deutan or tritan defect. An abnormality of red CFF with value lower than 31 Hz was revealed 51.7% (15/29) eyes. In the visual field, 58.6% (17/29) of eyes had paracentral scotoma, arcuate scotoma, or enlargement of physiologic blind spot. Contrast sensitivity was depressed in 62.1% (18/29) of eyes, mainly at middle and low spatial frequency. Pupil cycle time was prolonged in 72.4% (21/29) of eyes. Aside from visual acuity, other visual functions of the recovered ethambutol optic neuropathy patients were incomplete. The extent of recovery of the visual function is as follows: visual acuity-VEPs-color sense-CFF-visual field-contrast sensitivity-pupil cycle time.

Adult↗

PubMed1993

Accommodative adaptation and age of onset of myopia.

Tonic accommodation in an empty field and accommodative adaptation, defined as accommodation shift after 2 min viewing of a 4 D near task, were measured using an infrared optometer. Subjects were classified into three types: emmetropes (n = 18), early onset myopes (n = 18) and late onset myopes (n = 15). The relationship between accommodative adaptation and the onset age of myopia were compared. There was no statistical difference in the pre-task tonic accommodation among the three subject groups. However, the accommodative adaptation differed in the three groups during the 5 min post-task period. The average accommodative adaptation of emmetropia, early onset myopia and late onset myopia were 0.66, 0.27 and 1.19 D, respectively. Accommodative adaptation in the late onset myopia group was significantly higher than in the emmetropia group. Furthermore, the accommodative adaptation in the early onset myopia group was significantly lower than in the emmetropia group. Two possible aetiologies of myopia are discussed: one for the group which shows low accommodative adaptation that has no relationship with the age of onset and another for the group which shows high accommodative adaptation that has a relationship to an onset age of 15 years or later. The aetiology is also considered with regard to a potentiating chemical effect on the synapses of the ciliary muscle.

Accommodation, Ocular↗

PubMed1993

Critical flicker frequency in acute and recovered optic neuritis.

Multiple occasional changes in critical flicker frequency (CFF) were studied in patients who recovered from optic neuritis. Twenty-five patients (31 affected eyes) with onset visual acuity less than 0.5 and who showed recovered visual acuity exceeding 1.0 were included in this study. Recovery stages were determined individually as follows: T1, initial onset stage; T2, intermediate stage; T3, recovered stage when visual acuity was 1.0 or better; and T4, final follow-up stage. CFF was determined using red, yellow and green illuminated targets in a compact CFF measuring device recently developed at our department. The rates of abnormality were 100% at stage T1 for all colors, and gradually decreased as the stage advanced from T2 to T4. However, the rates of abnormality continued to be high at 67% in stage T3 for the red target and 37% in stage T4 for the red target. The rates of abnormal interocular difference in CFF in 15 unilateral optic neuritis patients were 100% for all colors at stage T1 and decreased gradually with recovery. Slight but definite abnormality of CFF was also noted in the silent eyes of clinically unilateral optic neuritis patients. The rates of abnormal CFF more than 7% in all colors could be detected in T1, T3 and T4. These results indicate that CFF abnormality can be detected even at the stage of recovery in the pathologic eyes and the fellow eyes of optic neuritis patients. CFF was also shown to be a sensitive indicator for detecting visual dysfunction in patients with optic neuritis.

Acute Disease↗