Modification of the Xenopus electroretinogram by actions of glycine in the proximal retina

The electroretinogram (ERG) was recorded from the Xenopus retina, to examine the effects of glycine and strychnine on these responses and to determine the origins of these changes. Glycine at concentrations between 0.1 and 10 mM reduced the b- and d-waves of the ERG in a dose-dependent manner, while strychnine increased their amplitude. 2-Amino-4-phosphonobutyric acid (APB) reduced the b-wave and blocked the effect of glycine, but not strychnine, on the d-wave. When the d-wave had first been blocked by kynurenic acid (KYN) or reduced by (+/-)cis-2,3-piperidine dicarboxylic acid (PDA) the b-wave was enhanced by glycine, but not by strychnine. N-methyl-DL-aspartate (NMDLA), which alters responses in the proximal retina only, blocked the effects of glycine and strychnine on the ERG. This suggests that the glycinergic effects on the ERG are at least partly mediated by processes in the proximal retina. The results further support the suggestion that inhibitory neurotransmitters in the proximal retina may modulate both the b- and d-waves of the Xenopus ERG.     

Laser treatment and the mechanism of edema reduction in branch retinal vein occlusion

PURPOSE: To test a hypothesis on the physiological mechanism of the disappearance of macular edema after laser treatment. The hypothesis is based on the effect grid laser treatment has on retinal oxygenation and hemodynamics. It predicts that laser-induced reduction of macular edema is associated with shortening and narrowing of retinal vessels in patients with branch retinal vein occlusion (BRVO). METHODS: The study included 12 subjects, treated with argon laser photocoagulation for BRVO and macular edema. Fundus photographs taken at the time of diagnosis and again after laser treatment, were digitized, and diameter and segment length of retinal vessels was measured using NIH-Image program. RESULTS: Macular edema disappeared or was dramatically reduced in all cases after laser treatment. The diameter of occluded venules constricted to 0.81+/-0.02 (mean +/- SD, P = 0.019) of the prelaser diameter and adjacent arterioles constricted to 0.78+/-0.01 (P = 0.008). The laser treatment also led to shortening of the affected vessels. The final segment length of the occluded venules was 0.95+/-0.17 (P = 0.005) of the length before treatment. The corresponding value for the adjacent arterioles is 0.95+/-0.14 (P = 0.008). Control arterioles and venules in the same fundus did not change in either length or width. CONCLUSIONS: These results do not reject the authors' hypothesis that the disappearance of macular edema in BRVO can be explained by the effect the laser photocoagulation has on retinal oxygenation. Increased oxygenation causes vessel constriction and shortening and lower intravascular pressure, which reduces edema formation according to Starling's law.     

Relationships between ocular dimensions and adult stature among participants in the Reykjavik Eye Study

PURPOSE: To examine the relationships between adult stature, age and ocular dimensions in a large homogenous, white population. METHODS: We used the national population census for Reykjavik to select a random sample of adults aged 50 years or older. A total of 846 persons were examined. Scheimpflug images were used to measure anterior chamber depth. Ultrasound was used to measure axial length, lens thickness and vitreous chamber depth. An autorefracto-keratometer was used to measure autorefractive and keratometric values, including the radius of the corneal curvature. Stereo fundus photographs were taken of the optic disc and measurements of the disc diameters were made using computer software. RESULTS: Height correlated positively with axial length in the multivariate model (B = 0.020, 95% CI 0.006-0.034, p < 0.01). Both age and height showed significant correlations with vitreous chamber depth, where the correlation with age was negative (B = - 0.016, 95% CI - 0.006 to - 0.025, p < 0.005) and the correlation with height was positive (B = 0.019, 95% CI 0.005-0.034, p < 0.01). Height also showed a positive correlation with the radius of the corneal curvature (B = 0.008, 95% CI 0.004-0.011, p < 0.001). Anterior chamber depth had a negative correlation with age (B = - 0.013, 95% CI - 0.010 to - 0.016, p < 0.001), whereas lens thickness had a significant positive correlation with age (B = 0.019, 95% CI 0.016-0.023, p < 0.001). We found a significant negative correlation between axial length and refraction/spherical equivalent (r = - 0.595, p < 0.0001). DISCUSSION: Our results indicate that there is a significant relationship between height and several ocular dimensions in this adult population and confirms a negative correlation between axial length and refraction.     

Twelve‐year Incidence of Exfoliation Syndrome in the Reykjavik Eye Study

Purpose: To examine the 12‐year incidence of exfoliation syndrome (XFS) in persons aged 50–79 years at baseline and also to monitor changes in related ophthalmologic variables, to identify possible risk factors for incidence and to estimate the reliability of our diagnostic criteria. Methods: Baseline examination was performed in 1996 on a random sample of 1045 participants from the population of Reykjavik, 50 years and older. Five years later, in 2001, 88.2% of survivors returned for a follow‐up. In 2008, 12 years after the baseline examination, a total of 573 participants returned for the third examination (71.5% of survivors). On all three occasions, the participants underwent a thorough eye examination including slitlamp examination specifically looking for XFS and answered a comprehensive questionnaire. Results: A total of 8.0% of participants developed XFS during the follow‐up period in at least one eye, with women being more commonly affected than men, 9.2% versus 6.6%. The overall 12‐year incidence for either eye increased with increasing age, from 6.5% in those participants aged 50–59 years at baseline to 10.6% in those that were 70–79 years at baseline; 71% of clinically unilateral cases had converted to bilateral over 12 years. Conclusions: Twelve‐year incidence of XFS is higher in women than in men and higher in older age groups than in younger ones. Most persons deemed on the slitlamp to be unilaterally affected have converted to bilateral over 12 years. Eyes with XFS at baseline were 3–4 times more likely to have cataract surgery during the 12 years. Our definition of definite XFS generally holds, while our definition of probable XFS is of no prognostic value over 12 years.     

The 7‐year cumulative incidence of cornea guttata and morphological changes in the corneal endothelium in the Reykjavik Eye Study

Purpose: To examine the corneal endothelium and establish the 7‐year cumulative incidence of cornea guttata (CG). Methods: Population‐based prospective cohort study with 573 participants (third wave of the Reykjavik Eye Study (RES) in 2008). Four hundred and thirty‐seven subjects had either right or left eyes available for analysis after excluding confounding eye conditions. The baseline for eyes at risk for developing CG is the second wave of the RES in 2001. Participants underwent specular microscopy and a standardized eye examination. Results: The cumulative 7‐year incidence of CG in either eye was estimated as a 95% confidence interval for the expected value for both genders combined (15–23%), for males (8–18%) and for females (19–29%). In right eye only, the 7‐year cumulative incidence for both genders combined was estimated to be 6–11%. For genders combined and for males only, the data indicated no correlation between 7‐year cumulated incidence and age at baseline. In women, however, the change of 7‐year incidence for CG in at least one eye appeared to be correlated to age at baseline. Reduction of endothelial cell density for corneas with CG at baseline was found [CI (0.95)?132 ± 94]. Conclusion: The cumulative 7‐year incidence of primary central CG for a middle‐aged and older Caucasian population without history of potentially confounding eye disease has been established. Women tend to have higher incidence if onset occurs at middle age. If CG is present, the cell density and the cell size variation decrease within a 7‐year period.     

Prevalence of open-angle glaucoma in Iceland: Reykjavik Eye Study

PURPOSE: To establish the age- and sex-specific prevalence of open-angle glaucoma (OAG) subsuming pseudoexfoliation (PEX) in the city of Reykjavik. METHODS: Participants 50 years of age and older who were part of the Reykjavik Eye Study and classified as having glaucoma were divided into three categories:Category 1: two or more of the following based on optic nerve stereophotograph reading: vertical cup to disc ratio (VCDR) 97.5th percentile (>0.7), focal glaucomatous disc change, C/D asymmetry of 97.5th percentile difference between eyes (>0.2) as well as glaucomatous visual field defect (GVFD).Category 2: 99.5th percentile of VCDR (>0.8) and 99.5% percentile difference between eyes (>/=0.3), without a GVFD.Category 3: VA<3/60 and IOP>99.5th percentile or VA <3/60 and evidence of filtering surgery. For a glaucoma suspect, one of the following was present: VCDR>99.5th percentile (>0.8), focal glaucomatous disc change, C/D asymmetry of 99.5th percentile (> or =0.3), GVFD only, IOP> or =23 mmHg (97.5 percentile). PEX was diagnosed by the presence of a central shield and/or a peripheral band on the anterior lens capsule. RESULTS: Of 42 persons (22 males and 20 females) with OAG, 13 (31.0%) had PEX. The minimum prevalence of OAG was 4.0% (42/1045) (95% CI 2.8-5.2) for those 50 years and older and 10.3% (95% CI 8.5-12.2) for PEX. The prevalence of OAG increases with age (OR=1.10/year, 95% CI 1.07-1.13, P=0.000) and the same applies for the prevalence of PEX, OR=1.10 (95% CI 1.07-1.12, P=0.000). CONCLUSION: There is a 10% annual increase for both OAG and PEX in persons 50 years and older.     

On the ocular refractive components: the Reykjavik Eye Study

PURPOSE: To study the correlation between ocular refraction and the refractive components (corneal power, lens power and axial length) in a population-based sample of normal subjects. METHODS: We analysed the refractive and biometric findings for 723 right eyes (325 males and 398 females) comprising a population-based random sample of citizens 55 years and older participating in the Reykjavik Eye Study. Measurements of refraction, corneal curvature (by keratometry), anterior chamber depth, lens thickness and axial length (all by ultrasound biometry) were used to calculate crystalline lens power. The correlation and regression between refraction and ocular refractive components (corneal power, anterior chamber depth, lens power and axial length) were studied by distributional statistical methods. RESULTS: Refraction (spherical equivalent) showed a significant negative correlation with axial length (r = -0.59, P < 0.0001), lens power (r = -0.26, P < 0.0001) and corneal power (r = -0.16, P < 0.0001). There were significant negative correlations between axial length and corneal power (r = -0.44, P < 0.0001) and between axial length and lens power (r = -0.44, P < 0.0001). Based on multiple linear regression analysis, refraction could be correlated with corneal power, lens power and axial length in combination with a correlation coefficient of 0.98 (P < 0.0001). CONCLUSION: This study confirms that ocular refraction is statistically significantly correlated with not only axial length but also lens power and (to a lesser extent) corneal power. The variation and correlations of crystalline lens power were considerable -- possibly indicating this component's modulatory effect on ocular refraction during growth. We conclude the refractive error of the eye to be a multifactorial condition involving a complex interplay between the cornea, the lens and the length of the eye.