The retinal oximeter is reliable, easy to use, and sensitive to changes in SO(2) when concentration of O(2) in inhaled air is changed.

ABSTRACT.Purpose: To establish a population profile of central corneal thickness (CCT), radius of the corneal curvature (CC) and intraocular pressure (IOP) and the relationships between them using non-contact techniques. Methods: We used a population-based random sample of 415 male and 510 female Caucasians aged 50 years and older. CCT and the radius of CC were measured with Scheimpflug anterior segment photography. IOP was measured with air-puff tonometry. Results: The mean IOP of right eyes was 15.1 mmHg (SD 3.3) among men and 15.8 mmHg among women (SD 3.1), which is a statistically significant difference. The mean radius of CC for male right eyes was 7.78 (SD 0.60) and for females 7.62 (SD 0.58) which is also statistically significant. Mean CCT for male right eyes was 0.528 mm (SD 0.041) and for females 0.526 mm (SD 0.037), which is not a significant difference. Linear regression analysis shows no relationship between the radius of CC and IOP or between age and radius of CC. Linear regression analysis of the relationship between CCT and IOP suggests higher IOP measurements with thicker corneas. There was no significant correlation between age and CCT. Conclusion: IOP was found to be independent of age and significantly higher in females than in males. Radius of CC was found to be age-independent and significantly steeper in females than in males. CCT appears to be independent of age and gender. Greater CCT is associated with higher mean IOP.Key words: population based study ª intra ocular pressure ª central corneal thickness ª corneal curvature ª Scheimpflug photography.

We investigated the effects of recreational exposure to the natural environment on mood and psychophysiological responses to stress. We hypothesized that walking in nature has restorative effects over and above the effects of exposure to nature scenes (viewing nature on TV) or physical exercise alone (walking on a treadmill in a gym) and that these effects are greater when participants were expected to be more stressed. Healthy university students ( N = 90) were randomly allocated to one of three conditions and tested during an exam-free period and again during their exam time. Mood and psychophysiological responses were assessed before and after the interventions, and again after a laboratory stressor. All interventions had restorative effects on cortisol levels ( p < .001), yet walking in nature resulted in lower cortisol levels than did nature viewing ( p < .05) during the exam period. Walking in nature improved mood more than watching nature scenes ( p < .001) or physical exercise alone ( p < .05).

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ABSTRACT.Purpose: To assess retinal vessel oxygen saturation and retinal vessel diameter in retinitis pigmentosa. Methods: A retinal oximeter (Oxymap ehf., Reykjavik, Iceland) was used to measure retinal vessel oxygen saturation and vessel diameter in ten patients with retinitis pigmentosa (RP) (mean age 49 years, range 23-71 years). Results were compared with age-and gender-matched healthy individuals. All patients had advanced stage of the disease with visual fields restricted to the macular region. Results: Oxygen saturation in retinal venules was 58.0 AE 6.2% in patients with RP and 53.4 AE 4.8% in healthy subjects (p = 0.017). Oxygen saturation in retinal arterioles was not significantly different between groups (p = 0.65). The mean diameter of retinal arterioles was 8.9 AE 1.6 pixels in patients with RP and 11.4 AE 1.2 in healthy controls (p < 0.0001). The corresponding diameters for venules were 10.1 AE 1.2 (RP) and 15.3 AE 1.7 (healthy, p < 0.0001). Conclusions: Increased venous saturation and decreased retinal vessel diameter suggest decreased oxygen delivery from the retinal circulation in retinitis pigmentosa. This is probably secondary to tissue atrophy and reduced oxygen consumption.

Lysosomal enzymes function optimally at low pH; as accumulation of waste material contributes to cell aging and disease, dysregulation of lysosomal pH may represent an early step in several pathologies. Here, we demonstrate that stimulation of the P2X7 receptor (P2X7R) for ATP alkalinizes lysosomes in cultured human retinal pigmented epithelial (RPE) cells and impairs lysosomal function. P2X7R stimulation did not kill RPE cells but alkalinized lysosomes by 0.3 U. Receptor stimulation also elevated cytoplasmic Ca(2+); Ca(2+) influx was necessary but not sufficient for lysosomal alkalinization. P2X7R stimulation decreased access to the active site of cathepsin D. Interestingly, lysosomal alkalinization was accompanied by a rise in lipid oxidation that was prevented by P2X7R antagonism. Likewise, the autofluorescence of phagocytosed photoreceptor outer segments increased by lysosomal alkalinization was restored 73% by a P2X7R antagonist. Together, this suggests that endogenous autostimulation of the P2X7R may oxidize lipids and impede clearance. The P2X7R was expressed on apical and basolateral membranes of mouse RPE; mRNA expression of P2X7R and extracellular ATP marker NTPDase1 was raised in RPE tissue from the ABCA4(-/-) mouse model of Stargardt's retinal degeneration. In summary, P2X7R stimulation raises lysosomal pH and impedes lysosomal function, suggesting a possible role for overstimulation in diseases of accumulation.

ABSTRACT.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.

Oxygen saturation in retinal blood vessels is higher in dark than in 80 or 100 cd/m(2) light in human retinal arterioles and venules. The authors propose that this is a consequence of increased oxygen demand in the outer retina in the dark.