Dong Hui Lim

Heritability of Myopia and Ocular Biometrics in Koreans: The Healthy Twin Study

PURPOSE To estimate the heritabilities of myopia and ocular biometrics among different family types among a Korean population. METHODS We studied 1508 adults in the Healthy Twin Study. Spherical equivalent, axial length, anterior chamber depth, and corneal astigmatism were measured by refraction, corneal topography, and A-scan ultrasonography. To see the degree of resemblance among different types of family relationships, intraclass correlation coefficients (ICC) were calculated. Variance-component methods were applied to estimate the genetic contributions to eye phenotypes as heritability based on the maximum likelihood estimation. Narrow sense heritability was calculated as the proportion of the total phenotypic variance explained by additive genetic effects, and linear and nonlinear effects of age, sex, and interactions between age and sex were adjusted. RESULTS A total of 240 monozygotic twin pairs, 45 dizygotic twin pairs, and 938 singleton adult family members who were first-degree relatives of twins in 345 families were included in the study. ICCs for spherical equivalent from monozygotic twins, pooled first-degree pairs, and spouse pairs were 0.83, 0.34, and 0.20, respectively. The ICCs of other ocular biometrics were also significantly higher in monozygotic twins compared with other relative pairs, with greater consistency and conformity. The estimated narrow sense heritability (95% confidence interval) was 0.78 (0.71-0.84) for spherical equivalent; 0.86 (0.82-0.90) for axial length; 0.83 (0.76-0.91) for anterior chamber depth; and 0.70 (0.63-0.77) for corneal astigmatism. CONCLUSIONS The estimated heritability of spherical equivalent and ocular biometrics in the Korean population suggests the compelling evidence that all traits are highly heritable.

Intraocular lens power calculations in a patient with posterior keratoconus.

Purpose: We describe a patient with posterior keratoconus accompanied by hyperopia and a cataract, which were successfully treated by cataract surgery and secondary piggyback intraocular lens (IOL) implantation. Methods: Case report. Results: A 47-year-old woman presented to our clinic with low vision in her right eye. Uncorrected distant visual acuity was 20/400 in the right eye with a manifest refraction of +11.5 diopters. On the slit-lamp examination, localized posterior keratoconus and lens opacity were noted in the right eye. First, we performed phacoemulsification and posterior chamber IOL implantation. Postoperatively, hyperopic shift was noted because localized posterior elevation of the cornea is not considered in the conventional IOL power calculation. After secondary piggyback IOL implantation in the sulcus, her refractive error was finally properly corrected and uncorrected distant visual acuity improved to 20/50. Conclusions: In patients with posterior keratoconus, IOL power calculation from conventional keratometry may be inaccurate, and secondary piggyback IOL procedure may be needed after cataract surgery.

Measurement of lens density using Scheimpflug imaging system as a screening test in the field of health examination for age-related cataract

Purpose To assess Pentacam (Oculus, Wetzlar, Germany) Scheimpflug quantitative images in evaluating lens density and providing objective measurements to suggest optimal time of cataract surgery in the field of health examination. Methods Two hundred and twenty-nine eyes with age-related cataract were enrolled. Lens density was measured using Pentacam. All Pentacam images were exported to ImageJ (NIH, Bethesda, Maryland, USA) for quantitative analysis. Average lens density (ALD) and nuclear lens density (NLD) were calculated. Lens density was also evaluated by built-in Pentacam Nucleus Staging (PNS) software. Slit-lamp microscopy was performed for cataract grading according to Lens Opacification Classification System III (LOCS III). The best-corrected visual acuity (BCVA) was measured. All measurements were compared between the cataract surgery and non-cataract surgery groups. Results The measurements of Pentacam images significantly correlated with LOCS III for nuclear opalescence (NO) and nuclear colour (NC) grading (p<0.01). Pentacam ImageJ showed higher correlation than PNS. The mean NLD was most highly correlated with NO (r=0.8833) and NC (r=0.6815). The maximum ALD was most highly correlated with cortical opacity (r=0.5381). All Pentacam measurements of lens density and BCVA were significantly different between the cataract surgery and non-surgery groups (p<0.01). The optimised cut-off values to perform cataract surgery for mean NLD and maximum ALD were 26 and 74, respectively (p<0.01). Conclusions The Pentacam ImageJ method provided objective measurements to evaluate cataracts needing surgery. The method has the potential to be generally applied in the field of health examination and is effective in screening patients with cataract.

Prospective contralateral eye study to compare 80- and 120-μm flap LASIK using the VisuMax femtosecond laser.

PURPOSE To compare visual outcomes and flap stability of LASIK with ultrathin 80- and 120-μm flaps created with a VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) for moderate to high myopia and to evaluate the effect of corneal flap thickness on outcomes. METHODS In a prospective contralateral eye study, 36 consecutive patients (72 eyes) underwent bilateral LASIK for myopia ranging from -2.00 to -10.00 diopters using the VisuMax femtosecond laser and MEL-80 excimer laser (Carl Zeiss Meditec). One eye of each patient was randomized to have the 80-μm flap and the other to the 120-μm flap created with 200-kHz VisuMax femtosecond laser. Preoperative and postoperative tests included visual acuity, manifest refraction, contrast sensitivity, and flap thickness measured by anterior segment optical coherence tomography. Main outcomes and complications were checked at postoperative 1 week and 1, 3, and 6 months. RESULTS There were no differences in visual outcome, residual refractive error, or contrast sensitivity between groups during follow-up, except for better uncorrected visual acuity at postoperative 1 day in the 120-μm group. Mean standard deviations of measured flap thickness during follow-up ranged from 3.16 to 3.80 μm in both groups. Opaque bubble layer, a unique complication in femtosecond LASIK, was more frequent in the 80-μm group (7 of 36: 19%) than in the 120-μm flap group (3 of 36: 8%) without a statistically significant difference (P = .301) and was related to thicker central cornea and steeper keratometric value, although it did not influence clinical results. Comparison of the intended versus achieved correction showed no significant differences between groups. CONCLUSIONS LASIK using the VisuMax femtosecond laser supplied good clinical results and flap reproducibility in both the 80- and 120-μm flap groups. Patients with relatively thin cornea may benefit from 80-μm flap LASIK.

Clinical results of posterior chamber phakic intraocular lens implantation in eyes with low anterior chamber depth.

PURPOSE To investigate visual outcomes of Visian implantable Collamer lens (ICL) implantation in eyes with a shallow anterior chamber depth (ACD). DESIGN Retrospective, noncomparative, interventional case series. METHODS Medical charts of the patients with a low ACD of 2.8 mm or less who underwent implantable Collamer lens implantation were reviewed. To evaluate efficacy and safety, preoperative and postoperative uncorrected visual acuity, manifest refractive spherical equivalent (MRSE), endothelial cell count, intraocular pressure, angle opening distance at 500 μm from the scleral spur, trabecular-iris angle, and postoperative central vault were analyzed. RESULTS The mean follow-up period for 18 eyes of 10 patients was 24.67 ± 15.09 months (range, 10 to 51 months). The preoperative ACD was 2.71 ± 0.08 mm (range, 2.42 to 2.79 mm). There was no postoperative endothelial cell count reduction to less than 2000 cells/mm(2) or intraocular pressure elevation to more than 21 mm Hg. The differences between preoperative and postoperative angle opening distance at 500 μm from the scleral spur and trabecular-iris angle were statistically significant (P = .000, both). The mean postoperative central vault was 331.83 ± 181.28 μm (range, 174 to 811 μm), which was significantly less than expected (P = .000). Anterior subcapsular cataract was observed in 2 eyes (11.1%). CONCLUSIONS Implantable Collamer lens implantation in shallow ACD eyes exhibited good visual outcomes. Severe complications did not develop over relatively long periods. Two cases of anterior subcapsular cataract developed in older aged patients, suggesting the need for thorough preoperative warning about the risk of cataract. In addition, a postoperative vault less than expected should be taken into account when determining implantable Collamer lens size in lower ACD eyes.

Factors affecting near vision after monofocal intraocular lens implantation.

PURPOSE To identify factors that influence near vision after monofocal intraocular lens (IOL) implantation for distance vision. METHODS A retrospective review was conducted of patients who underwent cataract surgery with monofocal IOL implantation from October 2009 to April 2010 at Samsung Medical Center. Eyes were classified as having good (⩾ J4) or poor (< J4) near vision. Factors analyzed included age, sex, intraocular lens (IOL) movement, axial length, pupil size, degree and type of astigmatism, IOL type, total aberration, and higher-order aberrations. Binary logistic regression and odds ratios with 95% confidence intervals were determined. RESULTS This retrospective study involved 84 eyes of 84 patients. Thirty-four eyes were classified as having good near vision and 50 eyes as having poor near vision. All groups had a postoperative uncorrected visual acuity greater than 0.2 logMAR (Snellen 20/32) and a refractive error within ± 0.5 diopter of spherical equivalent. Pupil size and axial length were inversely associated with good near vision (P = .034 and .039, respectively). A pupil size smaller than 2.6 mm and an axial length less than 23.0 mm resulted in better near vision than larger measurements after monofocal IOL implantation for distant target. CONCLUSIONS Among the factors analyzed, small pupil size and short axial length predicted good near vision after phacoemulsification and monofocal IOL implantation.

Visual Impairment of Korean Population: Prevalence and Impact on Mental Health.

PURPOSE We identified the prevalence and sociodemographic characteristics of people with visual impairment (VI), and determined the relationship between VI and mental health in the Korean population. METHODS This is a cross-sectional study using the database of the Korean National Health and Nutrition Examination Survey from 2008 through 2012. A total of 28,392 participants at 19 years of age or older with data of visual acuity and mental health questionnaire was included. Prevalence of VI and its association with sociodemographic factors were analyzed. Multivariate regression analyses were conducted to determine the association of VI with mental health. RESULTS Estimated prevalence of VI was 0.43% (95% confidence interval [CI], 0.35-0.52%) in adults aged 19 years and over. After adjusting for sex, the VI group was significantly older (P < 0.001). After adjusting for age and sex, the VI group showed increased odds ratios (ORs) for diabetes mellitus (P < 0.001), lower education (P < 0.001), no occupation (P = 0.046), restricted daily activity (P < 0.001), and being single (P = 0.002) compared to the control group. After adjusting for covariates, VI was not associated with any of mental health parameters (OR, 0.88 [95% CI, 0.53-1.47] for depressive symptom; 1.38 [0.91-2.09] for suicidal ideation; 1.26 [0.82-1.94] for perceived stress). However, restricted daily activity was the strongest risk factor for poor mental health (OR, 2.49 [2.22-2.79] for depressive symptom; 2.77 [2.51-3.06] for suicidal ideation; 2.30 [2.09-2.54] for perceived stress). CONCLUSIONS Visually impaired people showed significantly unfavorable sociodemographic status. Although VI was not directly associated with mental health, restricted daily activity and poor sociodemographic factors found in visually impaired people increased risk for poor mental health.

The Heritability of Corneal and Ocular Higher-Order Aberrations in Koreans: The Healthy Twin Study

PURPOSE To estimate the genetic influences on corneal and ocular higher-order aberrations (HoAs) in the Korean population. METHODS This was a prospective, family-based twin cohort study. A total of 1272 adult twins and their family members, who were part of the Korean Healthy Twin Study from 2007-2011, were included. Corneal and ocular HoAs were measured. The genetic influences on HoAs were investigated by using variance-component methods after adjusting for age and sex. Narrow-sense heritability was calculated. Intraclass correlation coefficients (ICCs) were used to calculate degrees of resemblance among different types of family relationships. RESULTS A total of 269 monozygotic (MZ) twin pairs (including 176 MZ twin pairs and 93 orphan twins), 50 dizygotic (DZ) twin pairs (including 38 DZ twin pairs and 12 orphan twins), and 739 adult first-degree relatives of twins in 358 families were included. For more than half of corneal HoAs, the narrow-sense heritability estimates were not significant. Horizontal coma was highly heritable among corneal HoAs. The ICCs of horizontal coma from MZ twin pairs, pooled first-degree pairs, and spouse pairs were 0.41, 0.05, and 0.00, respectively. Among ocular HoAs, the estimated narrow-sense heritability of SA was 0.71 with the highest estimates. The ICCs of spherical aberration (SA) from MZ twins, pooled first-degree pairs, and spouse pairs were 0.76, 0.25, and 0.06, respectively. CONCLUSIONS Both corneal and ocular HoAs demonstrated smaller heritability. Corneal HoAs showed low heritability, suggesting individual environmental factors explain most of the variance of these HoAs in the Korean population. Ocular HoAs were moderately heritable.

Gyrate atrophy of the choroid and retina diagnosed by ornithine-δ-aminotransferase gene analysis: a case report.

A pair of 19-year-old female identical twins was referred to our hospital with progressive visual loss. They exhibited bilateral chorioretinal atrophy involving the midperiphery on fundoscopy and fluorescein angiography. Bilateral visual field constriction was noted on dynamic Goldmann perimetry, and a markedly impaired response was observed on both photopic and scotopic electroretinograms. Cystoid macular edema was identified in both eyes on optical coherence tomography. Plasma levels of ornithine were elevated. Based on these observations, the patients were diagnosed with gyrate atrophy of the choroid and retina. The clinical diagnosis was confirmed by mutation analysis of the ornithine-δ-aminotransferase (OAT) gene. Patients were treated with a pyridoxine supplement (300 mg/day) and an arginine-restricted diet to lower plasma levels of ornithine, which were successfully reduced without progression of chorioretinal atrophy for 15 months. Our report describes the first case of gyrate atrophy in the Korean population diagnosed by OAT gene analysis and treated with vitamin B6 dietary supplementation.

Korean patients taking α1-adrenergic receptor antagonists show lower incidence of intraoperative floppy iris syndrome than western patients

Purpose To evaluate the incidence and clinical manifestations of intraoperative floppy iris syndrome (IFIS) according to iris alterations in Korean patients taking α1-adrenergic receptor antagonists (α1-ARAs). Methods This is a prospective observational study. Two surgeons performed cataract surgery in 758 eyes of 596 patients over a period of 12 months. Past medical history was reviewed, especially whether patients had been taking systemic α1-ARAs. Ultrasound biomicroscopy was performed to measure the iris thickness of the dilator muscle region (DMR) at half the distance between the scleral spur and the pupillary margin. Pupil diameter was measured and the occurrence of IFIS was recorded. Measurements of the α1-ARA group were compared with those of a control group matched for age and sex. Results IFIS occurred only in six eyes of four patients on systemic α1-ARA medications (0.8%). Pupil diameter in the α1-ARA medication group and the control group was not significantly different. The difference in mean DMR thickness in patients taking an α1-ARA and in the control group was also not statistically significant (p=0.641). However, within the α1-ARA population, the DMR thickness of IFIS cases was significantly lower than that of non-IFIS cases (p=0.013) Conclusions The overall incidence of IFIS was far lower in Korean patients than that reported for western patients. IFIS patients taking α1-ARAs showed significantly greater iris DMR thinning than non-IFIS patients taking α1-ARAs. Our findings indicate that the interaction between α1-ARAs and melanin, which results in iris DMR atrophy and IFIS, is less strong in Korean patients (with dark irises) than western patients.