Lens thickness and insulin dependent diabetes mellitus: a population based twin study.

AIM: To investigate the relation between lens thickness and duration of insulin dependent diabetes mellitus (IDDM). METHODS: From the new population based Danish twin register, containing 20,888 twin pairs born between 1953 and 1982 (inclusive), all twin pairs having one or both partners affected with IDDM were searched. Among the 45 twin pairs available for clinical eye examination there were 15 monozygotic pairs, 14 dizygotic pairs of same sex, and 16 dizygotic pairs of opposite sex. Lens thickness was measured by ultrasonography. Using a twin control design, the relation between lens thickness and duration of IDDM was assessed by estimating the correlation between the intrapair difference in lens thickness and the intrapair difference in diabetes duration. RESULTS: In monozygotic twin pairs a statistically highly significant correlation between duration of diabetes and lens thickness was found (right eye: r = 0.88, p < 0.0001; left eye: r = 0.90, p < 0.0001). In dizygotic twin pairs of the same sex the correlations were r = 0.58 (p = 0.029) and r = 0.53 (p = 0.053) for right eye and left eye, respectively. For dizygotic twin pairs of opposite sex the correlations were r = 0.58 (p = 0.018) and r = 0.69 (p = 0.005) for right eye and left eye, respectively. The slope in regression analysis were similar for monozygotic twin pairs (0.025, common for both eyes) and dizygotic twin pairs grouped (0.024, common for both eyes). CONCLUSIONS: There is a statistically significant positive correlation between duration of IDDM and lens thickness, as assessed by the twin control method. The higher correlation in monozygotic twins compared with dizygotic twins suggests that genetic factors play an additional role in the determination of lens thickness. The similar slopes in regression analysis indicate that the effect of diabetes duration on lens thickness is independent of zygosity.     

Heritability of cilioretinal arteries: a twin study

PURPOSE: To determine whether the presence of one or more cilioretinal arteries, a distinct element of the pattern of fundus vessels, is genetically programmed, influenced by environmental factors, or the result of random mechanisms of vascular development. METHODS: The fundi of 112 pairs of healthy monozygotic and dizygotic twins were examined using digital fundus photography and visual assessment of grayscale fundus photographs and color transparencies to detect the presence of cilioretinal arteries. RESULTS: Cilioretinal arteries were present in 45.1% of participants and 28.8% of eyes. The majority of cilioretinal arteries, 88.2%, were located temporally, and 11.8% were located nasally. Monozygotic twins had higher concordance rates for cilioretinal arteries than dizygotic twins. Tetrachoric correlations and Mantel-Haenszel odds ratios demonstrated statistically significant evidence of a genetic effect underlying the presence of cilioretinal arteries (P < 0.01). Statistical analysis supported the hypothesis that additive genetic factors influenced the presence of cilioretinal arteries with a heritability of 71.4%, the remaining variance being attributable to nonshared or random environmental factors. CONCLUSIONS: The presence or absence of one or more cilioretinal arteries in healthy persons is markedly influenced by genetic factors.     

Heritability of anterior chamber depth as an intermediate phenotype of angle-closure in Chinese: the Guangzhou Twin Eye Study

PURPOSE: To assess the heritability of anterior chamber depth (ACD) and relative anterior chamber depth (ACD/axial length, rACD) in Chinese in a classic twin study. METHODS: Twins aged 7 to 15 years living in two local districts were recruited from the Guangzhou Twin Registry. Anterior chamber depth and axial length were measured by partial coherence laser interferometry. Zygosity in all same-sex twin pairs was confirmed by genotyping with 16 polymorphic markers. The phenotypes of the right eyes were used in analysis. Heritability was assessed by structural variance component genetic modeling. RESULTS: In total, 1126 twin participants were available for analysis, including 357 monozygotic (MZ) and 206 dizygotic (DZ) twin pairs. ACD increased with age (0.036 mm per year, P < 0.001) and 0.09 mm shallower in the girls than in the boys (P < 0.001). Age- and sex-adjusted intraclass correlation coefficients (ICCs) for ACD were 0.92 for the MZ and 0.50 for the DZ twins; those for rACD were 0.89 for the MZ and 0.52 for the DZ twins. The best-fitting model yielded 90.1% (95% CI: 88.2%-91.7%) of additive genetic and 9.9% (95% CI: 8.3%-11.8%) of unique environmental effects for ACD and 89.2% (95% CI: 87.1%-90.9%) of additive genetic and 10.8% (95% CI: 9.1%-12.9%) of unique environmental effects for rACD. CONCLUSIONS: Additive genetic effects appear to be the major contributor to the variation of ACD and rACD in Chinese population. High heritability remained even when the data were corrected for the influence of myopia.     

The importance of genes and environment for ocular refraction and its determiners: a population based study among 20-45 year old twins

AIMS: To estimate the heritability for ocular refraction and its determiners in a population based cohort of 20-45 years old twins. METHODS: 114 twin pairs (53 monozygotic and 61 dizygotic) participated. Refraction was determined in cycloplegia and eye dimensions were measured with ultrasound. Educational length was assessed. The heritability was estimated employing aetiological model fitting. Evidence of gene-environment interaction was analysed. Correlations between intrapairwise differences in educational length and in refraction were evaluated. RESULTS: The heritability was between 0.89 and 0.94 (95% CI: 0.82, 0.96) for refraction, total refraction, axial length, and radius of corneal curvature. Phenotypic variation was mostly due to additive genetic effects. Refraction revealed evidence of gene-environment interaction (r = -0.29 to -0.32; p <0.05). The heritability for anterior chamber depth and lens thickness was between 0.88 and 0.94 (95% CI: 0.81, 0.96) and dominant genetic effects were the most likely explanation. There was no correlation between age and intrapairwise differences in refraction. The dizygotic twins had significant larger intrapairwise differences in educational length (p <0.05), but the differences were not correlated with differences in refraction. CONCLUSIONS: The results indicate a high heritability for ocular refraction and its determiners and thus suggest that environmental impact on refraction is not significant. However, the epidemiological association between educational length (near work) and myopia, the evidence of increasing myopia prevalence within a few generations, and the theory of gene-environment interaction imply that some individuals might be genetically liable to develop myopia if exposed to certain environmental factors.     

Ability of spectral domain optical coherence tomography peripapillary retinal nerve fiber layer thickness measurements to identify early glaucoma

Purpose:

To evaluate the ability of spectral domain optical coherence tomography (OCT) peripapillary retinal nerve fiber layer thickness (RNFLT) parameters to distinguish normal eyes from those with early glaucoma in Asian Indian eyes.

Design:

Observational cross-sectional study.

Materials and Methods:

One hundred and seventy eight eyes (83 glaucoma patients and 95 age matched healthy subjects) of subjects more than 40 years of age were included in the study. All subjects underwent RNFLT measurement with spectral OCT/ scanning laser ophthalmoscope (SLO) after dilatation. Sensitivity, specificity and area under the receiving operating characteristic curve (AROC) were calculated for various OCT peripapillary RNFL parameters.

Results:

The mean RNFLT in healthy subjects and patients with early glaucoma were 105.7 ± 5.1 μm and 90.7 ± 7.5 μm, respectively. The largest AROC was found for 12 o’clock- hour (0.98), average (0.96) and superior quadrant RNFLT (0.9). When target specificity was set at ≥ 90% and ≥ 80%, the parameters with highest sensitivity were 12 o’clock -hour (91.6%), average RNFLT (85.3%) and 12 o’ clock- hour (96.8 %), average RNFLT (94.7%) respectively.

Conclusion:

Our study showed good ability of spectral OCT/ SLO to differentiate normal eyes from patients with early glaucoma and hence it may serve as an useful adjunct for early diagnosis of glaucoma.     

Glaucoma detection by Stratus OCT

PURPOSE: To investigate the diagnostic accuracy of retinal nerve fiber layer thickness (RNFLT) summary report parameters from Stratus optical coherence tomography (OCT) in glaucoma patients. PATIENTS AND METHODS: We obtained Stratus OCT measurements of peripapillary circle scans (average values) of the regular image resolution "FAST RNFLT" protocol, and of 1 circle scan of the high resolution "RNFLT" protocol in one eye of each of 62 glaucoma patients with mild or moderate visual field (VF) loss and 90 healthy subjects. Sensitivity, specificity, and diagnostic accuracy [(true positive+true negative)/all] were evaluated for all summary report parameters including the newer (eg, "Imax," the maximum thickness point in the inferior quadrant) at the normative limits of the Stratus OCT. RESULTS: The diagnostic accuracy of full circle RNFLT using the 5% normal limit was 89% with the FAST RNFLT and 87% with the RNFLT protocol; this was at least as good as any other parameter. The diagnostic performance of the 2 protocols did not differ significantly for most parameters. In eyes with mild VF loss (n=39) diagnostic sensitivities reached 72% and 77% at specificities >or=95% using the FAST RNFLT and RNFLT protocol, respectively. CONCLUSIONS: The diagnostic accuracy of the full circle RNFLT was as good as any Stratus OCT parameter on the basis of the peripapillary RNFL thickness measurements, including localized measurements. The sensitivity was moderately high in patients with mild glaucomatous VF loss. There seems to be room for further development of OCT interpretation tools for early diagnosis of glaucoma.     

Effect of vitamin B12 deficiency anemia on peripapillary retinal nerve fiber layer

AIM: To evaluate the effect of vitamin B12 deficiency anemia (BDA) on peripapillary retinal nerve fiber layer thickness (RNFLT) using spectral domain optical coherence tomography (SD-OCT), and to determine any correlation arising thereof. METHODS: In this cross-sectional observational study, 99 eyes of 50 BDA patients of age 18-65y were compared with 100 eyes of 50 healthy control subjects. All subjects underwent comprehensive clinical, ophthalmic, and hematological evaluation, followed by peripapillary RNFLT assessment using SD-OCT. RESULTS: The mean total, inferior, nasal, and temporal RNFLT were significantly lower in BDA group as compared to control group (P<0.05). The mean total, inferior and nasal RNFLT correlated significantly (P<0.05) with serum Hb%, B12 and mean corpuscular volume (MCV) level (r=0.310, 0.435, -0.386 for total; r=0.932, 0.481, -0.513 for inferior; r=0.344, 0.254, -0.233 for nasal; respectively), while temporal and superior RNFLT quadrant did not show any correlation with any of the hematological parameters (r=0.144, 0.167, -0.096; r=0.111, 0.070, -0.099; respectively). The mean total RNFLT showed progressive thinning at par with the progression of anemia, except in very severe BDA, where an inverse relationship was documented. CONCLUSION: The mean total, inferior, nasal, and temporal peripapillary RNFLT was significantly thinner in BDA patients. Peripapillary RNFLT thinning seemed to proceed at par with the progression of severity of anemia, except in very sever grade. Early assessment of peripapillary RNFLT may be crucial in BDA patients to prevent potential blinding sequelae. Peripapillary RNFLT thinning in BDA patients should be considered in the differential diagnosis of other non-glaucomatous optic neuropathies, as well.     

Influence of disc area on retinal nerve fiber layer thickness measurement by spectral domain optical coherence tomography

Background:

To examine the effect of optic disc area on peripapillary RNFLT (retinal nerve fiber layer thickness) measurement at circle diameter of 3.4 mm around optic nerve head using spectral OCT/SLO (Optical coherence tomography/scanning laser ophthalmoscope).

Materials and Methods:

In this prospective, cross sectional study, one hundred and two eyes of 102 normal subjects underwent RNFLT and disc area measurement using spectral OCT/SLO. Based on disc area, subjects were divided into three groups i.e., <3 mm² (32 eyes), 3-4 mm² (36 eyes) and >4 mm² (34 eyes). The effect of disc area on RNFLT parameters was analyzed using linear regression analysis.

Results:

The mean and quadrant RNFLT did not show significant correlation with disc area in subjects with disc area of <4 mm², however in eyes with disc area >4 mm², average RNFLT, superior and temporal quadrant RNFLT showed negative correlation with disc area, which was statistically significant (P = 0.004, P = 0.005 and P = 0.002, respectively)

Conclusion:

In healthy eyes of disc area <4 mm², disc size does not appear to affect peripapillary RNFLT measurement by spectral OCT/SLO. Average, superior and temporal quadrant RNFLT measurements were inversely proportional to disc area in eyes with disc area >4 mm². Hence, RNFLT measurement by OCT in eyes with optic disc area of >4 mm² should be interpreted carefully.     

Heritability of macular thickness determined by optical coherence tomography

PURPOSE: To examine whether genetic factors significantly influence macular thickness in healthy older subjects. METHODS: A classic twin study was performed to compare the correlation of macular thickness between monozygotic (MZ) and dizygotic (DZ) twins in a sample of population-based volunteer twins. The study included 109 white twin pairs from 50 to 80 years of age without evidence of manifest eye disease and corrected visual acuity better than 6/7.5. Dilated macular optical coherence tomography (OCT), fundus photography, clinical examination, ocular biometry, a health-dietary questionnaire, and subjective autorefraction were performed on all subjects. RESULTS: Correlation of retinal thickness was significantly greater between MZ twin pairs than DZ pairs in all macular regions. The MZ-to-DZ correlation was 0.88:0.44 for the foveal region, 0.79:0.47 for the inner macular region, and 0.81:0.50 for the outer macular region. With adjustment for significant covariates and model fitting, final heritability estimates of 85%, 81%, and 81%, respectively, were obtained. A significant correlation between foveal thickness and gender was present, with the men having significantly thicker foveae. There was a significant negative correlation between outer macular thickness and axial length. CONCLUSIONS: This study confirms that macular thickness in older healthy subjects, as measured by OCT, may be affected by genetic factors. Factors such as axial length, gender and age, warrant further examination in larger population-based studies, as variables that may influence macular thickness. This finding suggests an inherited basis of macular thickness and may help in the understanding of the factors that govern macular structure and function.     

特发性脱髓鞘性视神经炎所致视神经萎缩盘周视网膜神经纤维层厚度及黄斑厚度的定量研究

目的  应用相干光断层扫描（OCT）分析特发性脱髓鞘性视神经炎（IDON）所致视神经萎缩眼的视网膜神经纤维层厚度（RNFLT）和黄斑厚度（MT）的变化及其与病程和最佳矫正视力（BCVA）的相关性。设计  回顾性病例系列。研究对象  眼底表现视盘色苍白确定为视神经萎缩的IDON患者16例（16眼）及性别年龄匹配的健康对照23例（23眼）。方法  回顾OCT和BCVA检查结果,对比分析两组RNFLT和MT的差异,平均RNFLT和黄斑容积平均厚度的关系以及RNFLT和MT与病程和BCVA的线性相关关系。主要指标  平均（360°）RNFLT、四个象限RNFLT、黄斑容积平均厚度、ETDRS栅格9个分区的MT、病程及BCVA。结果  与正常对照相比,病例组360°平均和四个象限RNFLT均显著变薄（P均=0.00）,除中心子区外（P=0.25）,其余分区MT和黄斑容积平均厚度均显著变薄（P均=0.00）。平均RNFLT与黄斑容积平均厚度存在直线相关关系（r=0.662,P=0.01）,平均RNFLT和黄斑容积平均厚度与病程均无直线相关关系（P=0.70,P=0.13）。平均RNFLT和黄斑容积平均厚度与BCVA均无直线相关关系（P=0.80,P=0.28）。结论  有视神经萎缩的IDON患者除黄斑中心子区MT无显著变化外,其余分区MT和所有象限RNFLT均显著变薄,黄斑容积平均厚度与平均RNFLT存在线性相关关系,RNFLT越薄黄斑容积平均厚度越薄。RNFLT和黄斑容积平均厚度与病程和BCVA无线性相关关系。（眼科, 2013, 22: 130-134）     

Genetic factors in open-angle (simple and capsular) glaucoma. A population-based twin study

A nationwide record linkage of the Finnish Twin Cohort Study (FTCS) with the Hospital Discharge Registry and the Registry of Rights for Free medication is presented. This study consists of 108 pairs (114 individuals) of twins with chronic open-angle glaucoma. Of the twin pairs 29 were monozygotic (MZ), while 79 pairs were dizygotic (DZ). Three monozygotic and 3 dizygotic pairs were concordant for chronic open-angle glaucoma (OAG), while 26 monozygotic and 76 dizygotic pairs were discordant. Seventy-three twins had chronic simple glaucoma, while 34 twins had capsular glaucoma, and in 7 patients chronic simple glaucoma was noted in one eye and capsular glaucoma in the second eye. The heritability of chronic open angle glaucoma was 13%. The higher O/E-ratio of concordant twin pairs among MZ twins indicates that genetic factors play a role in this disease. The difference is anyhow surprisingly low compared to former estimates of heritability of open angle glaucoma. The steep rise in prevalence in older age groups was confirmed. The age-adjusted prevalence of chronic open-angle glaucoma in this study was 0.63%.     

Effectiveness of averaging strategies to reduce variance in retinal nerve fibre layer thickness measurements using spectral-domain optical coherence tomography

Background

Automated detection of subtle changes in peripapillary retinal nerve fibre layer thickness (RNFLT) over time using optical coherence tomography (OCT) is limited by inherent image quality before layer segmentation, stabilization of the scan on the peripapillary retina and its precise placement on repeated scans. The present study evaluates image quality and reproducibility of spectral domain (SD)-OCT comparing different rates of automatic real-time tracking (ART).

Methods

Peripapillary RNFLT was measured in 40 healthy eyes on six different days using SD-OCT with an eye-tracking system. Image brightness of OCT with unaveraged single frame B-scans was compared to images using ART of 16 B-scans and 100 averaged frames. Short-term and day-to-day reproducibility was evaluated by calculation of intraindividual coefficients of variation (CV) and intraclass correlation coefficients (ICC) for single measurements as well as for seven repeated measurements per study day.

Results

Image brightness, short-term reproducibility, and day-to-day reproducibility were significantly improved using ART of 100 frames compared to one and 16 frames. Short-term CV was reduced from 0.94?±?0.31 % and 0.91?±?0.54 % in scans of one and 16 frames to 0.56?±?0.42 % in scans of 100 averaged frames (P?≤?0.003 each). Day-to-day CV was reduced from 0.98?±?0.86 % and 0.78?±?0.56 % to 0.53?±?0.43 % (P?≤?0.022 each). The range of ICC was 0.94 to 0.99. Sample size calculations for detecting changes of RNFLT over time in the range of 2 to 5 μm were performed based on intraindividual variability.

Conclusion

Image quality and reproducibility of mean peripapillary RNFLT measurements using SD-OCT is improved by averaging OCT images with eye-tracking compared to unaveraged single frame images. Further improvement is achieved by increasing the amount of frames per measurement, and by averaging values of repeated measurements per session. These strategies may allow a more accurate evaluation of RNFLT reduction in clinical trials observing optic nerve degeneration.     

Modelling the normal retinal nerve fibre layer thickness as measured by Stratus optical coherence tomography

Background The variation in retinal nerve fibre layer thickness (RNFLT) as measured by Stratus optical coherence tomography (OCT) in healthy subjects may be reduced when the effect on RNFLT measurements of factors other than disease is corrected for, and this may improve the diagnostic accuracy in glaucoma. With this perspective we evaluated the isolated and combined effects of factors potentially affecting the Stratus OCT RNFLT measurements in healthy subjects.Methods We included 178 healthy eyes of 178 subjects between 20 and 80 years of age. Participants underwent an extensive eye examination. Stratus OCT RNFLT was measured by three standard protocols, two with high and one with standard image resolution. Effects on RNFLT of age, gender, refractive error, axial length, lens nuclear colour and opalescence, intra-ocular pressure (IOP), and optic disc size were examined by univariate and multivariate analyses.Results Age, refractive error, axial length, and lens nuclear colour and opalescence affected RNFLT in univariate analyses, whereas gender, IOP, and optic disc size had no significant effect. In multivariate analyses only age in combination with refractive error, or with axial length, was significant and explained 14.7–17.6% (R ²) of the total variation of RNFLT, approximately 50% more than age alone. RNFLT decreased by 2.6–2.9 μm per increasing decade of age and increased by 1.5–1.8 μm per more positive diopter of spherical equivalent using full-circle measurements of the three standard protocols. These effects varied between measurement sectors.Conclusions RNFLT as measured by Stratus OCT standard protocols was significantly affected by age and refractive status. The effect on global RNFLT of a difference in refractive error of 10 diopters corresponded to the effect of a difference in age of 60 years. Theoretically, the effect of refractive status may be explained by artefacts of RNFLT measurement circle placement. The results suggest that the diagnostic accuracy of Stratus OCT may be improved by considering refractive status in addition to age when RNFLT is measured. For this purpose spherical equivalent seems as effective as axial length.     

Corneal endothelial cells in mono- and di-zygotic twins

Noncontact specular microscopy was used to examine the corneal endothelia of monozygotic (MZ) and dizygotic (DZ) twins in the age groups 25-34, 35-49, and 50-69 years. Endothelial photographs were analysed in respect of 100 individual cells from both eyes of 48 subjects. The mean cell areas in MZ twins showed a strong positive pairwise correlation (r (RE) = 0.727, r (LE) = 0.933), but there was no statistically significant pairwise correlation in DZ twins (r (RE) = 0.080, r (LE) = 0.167). Statistically significant pairwise correlations were also found when the lowest or highest deciles of cell areas in MZ twins were compared, but not when respectively compared in DZ twins. It would seem that environmental factors have little effect upon pleomorphism and increase in cell area with increasing age. The endothelial cell characteristics in normal individuals seem to be mainly determined by genetic factors.     

Central corneal thickness is highly heritable: the twin eye studies

PURPOSE: A classic twin study was performed to determine the heritability of central corneal thickness (CCT), an important parameter in glaucoma assessment. METHODS: The concordance of CCT between monozygotic (MZ) and dizygotic (DZ) twins was compared. A total of 256 twin pairs (131 MZ and 125 DZ) were recruited from three centers: the Twin Eye Study in Tasmania, the Brisbane Adolescent Twin Study, and the Twins U.K. Adult Registry held at St. Thomas' Hospital in London. As part of an extensive ophthalmic evaluation, CCT was measured by ultrasound pachymetry. Structural equation modeling with the Mx program (Department of Psychiatry, Medical College of Virginia, Richmond, VA) was used to determine the heritability of CCT. RESULTS: The mean age of subjects was 38 years (range, 8-81). The mean CCT of all eyes examined was 544.5 +/- 37.3 mum (SD). The CCT measurements correlated more highly in MZ twins than in DZ twins, with intraclass correlation coefficients of 0.95 and 0.52, respectively, suggesting a strong genetic influence. A model of additive genetic and unique environmental effects provided the best fit, yielding a heritability of 0.95 (95% confidence interval [CI], 0.93-0.96) with the remaining variation being attributable to unique environmental factors. CONCLUSIONS: In this study of Australian and U.K. twins, genetic factors were shown to be of major importance in CCT, with a heritability of 0.95.     

Genetic influence on early age-related maculopathy: a twin study

OBJECTIVE: Age-related macular degeneration (AMD) is the most common cause of blindness in industrialized countries. There has been considerable interest in the genetics of early age-related maculopathy (ARM) and AMD, because they have phenotypes similar to inherited diseases where mutations have been identified, but the heritability of ARM and AMD is unknown. DESIGN: A classical twin study was performed to compare the concordance in monozygotic (MZ) and dizygotic (DZ) twins in an unselected sample of female volunteer twins. PARTICIPANTS: Five hundred six twin pairs, 226 MZ and 280 DZ, with a mean age of 62 years, were examined. METHODS: ARM was graded from stereoscopic macular photographs of 501 of the twin pairs (99%) according to the International ARM Epidemiologic Study Group grading system. The casewise concordance was calculated for twin pairs from 2 x 2 contingency tables of affected/unaffected twins, and these tables were used in maximum likelihood genetic modeling to estimate the heritabilities of phenotypes graded. MAIN OUTCOME MEASURES: Prevalence of ARM; concordance in MZ and DZ twins of the phenotypes of ARM, soft drusen >63 microm and > or =125 microm diameter, pigmentary changes and hard drusen (<20 and > or =20 in number); heritability of ARM and subphenotypes. RESULTS: The overall prevalence of ARM was 14.6% (95% confidence interval [CI], 12.4%-16.8%). The concordance for ARM in MZ twins was 0.37 compared with 0.19 in DZ twins, suggesting a role for genes. Modeling confirmed a genetic effect for phenotypes of ARM, soft drusen, pigmentary changes, and > or =20 hard drusen, although there was little genetic effect for scattered (<20) hard drusen. The heritability of ARM was estimated as 45% (95% CI, 35%-53%). The most heritable phenotypes were soft drusen > or =125 microm (57%) and > or =20 hard drusen (81%), with the latter being dominantly inherited. CONCLUSIONS: This study confirms a significant genetic influence in ARM and suggests that future genetic studies should examine phenotypes of large (> or =125 microm) soft drusen and > or =20 hard drusen, because these seem to be the most heritable components.     

Twin study on cup/disc ratio of the optic nerve head.

Seventeen healthy twin pairs (10 monozygotic and seven dizygotic) from the Finnish Twin Cohort Study were examined to study the impact of heredity v environment in the determination of cup-to-disc area ratio. These twins were free from any known eye disease. The cup/disc ratio was determined using stereo photography and a computer assisted analysis technique. The zygosity of all twin pairs was confirmed with the DNA 'fingerprint' technique. The intrapair correlations were high among monozygotic pairs compared with those among dizygotic twin pairs. The difference of cup/disc area ratios between the right eyes of members of monozygotic twin pairs was statistically significantly smaller than that of dizygotic twin pairs (p < 0.001). The same was true for left eyes (p < 0.01). This result confirms a genetic determination in cup/disc area ratio in normal eyes.     

The inheritance of peripapillary atrophy

PURPOSE: To estimate the relative importance of genes and environment in peripapillary atrophy type beta (beta-PPA) in a classic twin study. METHODS: Female twin pairs (n = 506) aged 49 to 79 years were recruited from the St. Thomas' UK Adult Twin Registry. Peripapillary atrophy was identified from masked grading of stereoscopic optic disc photographs. Structural equation modeling was performed using Mx with polychoric correlations of beta-PPA and refractive error (divided into deciles). RESULTS: Beta-PPA prevalence was 25.1% and did not vary with zygosity. Case-wise concordance for right eyes was 0.76 (95% CI, 0.57-0.88) for monozygotic (MZ) and 0.37 (95% CI, 0.15-0.56) for dizygotic (DZ) pairs. Multivariate modeling suggested additive genetic effects and individual environment, with no shared environment or dominant genetic effect. Beta-PPA heritability was 0.70 (95% CI, 0.54-0.83), and spherical equivalent 0.88 (95% CI, 0.85-0.91); age had no significant effect on variance. The genetic correlation between beta-PPA and spherical equivalent was -0.21. However, only 3% of the genetic variance of beta-PPA was explained by genetic factors in common with refractive error, with 67% explained by specific genetic factors for beta-PPA. Of the 30% of variance explained by unique environmental factors, only 3% was explained by these factors in common with environmental factors involved in refractive error. CONCLUSIONS: The presence of beta-PPA, a frequent ocular finding known to be associated with open-angle glaucoma, appears to be under strong genetic control, with only a small amount of this genetic effect shared with genes involved in myopia.     

The nerve fibre layer symmetry test: computerized evaluation of human retinal nerve fibre layer thickness as measured by optical coherence tomography

PURPOSE: To present and test a new interpretative concept, the nerve fibre layer symmetry test (NST), for computerized evaluation of retinal nerve fibre layer thickness (RNFLT) as measured by optical coherence tomography (OCT) in glaucoma. METHODS: The NST concept was constructed and tested in a pilot study. A total of 32 healthy and 40 age-matched glaucomatous eyes were included and examined by OCT, computerized perimetry, RNFL/disc photography, tonometry and a general ophthalmologic examination. RESULTS: The observed NST sensitivity and specificity were high, at 38/40 eyes (95%) and 32/32 eyes (100%), respectively, and 40/40 eyes (100%), and 31/32 eyes (97%), respectively, when correcting the OCT RNFLT measurement for the influence of variability in image signal/quality. The NST sensitivity was 8-10% higher than the single most sensitive traditional OCT RNFLT parameter; this difference was not statistically significant in this small sample. CONCLUSION: The NST showed high specificity and sensitivity for detection of RNFLT attenuation indicating early to severe glaucoma. Although promising, the NST needs to be further developed and validated in larger study samples and in patients with various stages of glaucomatous damage.     

7～18岁近视青少年视网膜神经纤维层厚度及其影响因素的分析

目的 探讨近视青少年视乳头旁视网膜神经纤维层厚度(RNFLT)的变异程度与年龄、屈光度、眼轴长度、性别及眼别的关系.方法 横断面调查研究.应用Stratus相干光断层扫描(OCT)仪的快速扫描程序,测量154例(154只眼)7～18岁近视青少年的视乳头旁全周和各象限平均RNFLT,并用A超测定眼轴长度.在进行影响因素分析时先行双变量直线回归分析,对差异有统计学意义的因素再进行多元线性逐步回归分析.结果 154只眼的全周平均RNFLT为(114.106±11.473)μm.按象限划分RNFLT从厚到薄依次为上方(145.468±19.064)μm,下方(138.091±20.464)μm,颞侧(94.396±18.544)μm,鼻侧(7 8.558±16.981)μm.双变量简单直线回归分析显示患者全周和上方RNFLT与其年龄(r=0.129,0.014)、屈光度数(r=0.006,0.123)、眼轴长度(r=-0.067,-0.141)、性别(r=-0.095,0.025)、眼别(r=-0.148,0.095)均无相关性(P＞0.05).多元线性逐步回归分析,显示患者颞侧RNFLT与其等效球镜度数呈负相关(r=-0.465,P＜0.05);鼻侧RNFLT与其眼轴长度(r=-0.327)和眼别(r=-0.327)均呈负相关(P＜0.05);下方RNFLT与其眼轴长度(r=-0.276,P＜0.05)呈负相关,但与其年龄呈正相关(r=0.276,P＜0.05).结论 在评价青少年的全周及各象限RNFLT时,需考虑其年龄、近视程度、等效球镜度数、眼轴长度及眼别的影响.