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Early detection of changes in visual function in diabetes mellitus
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Ophthal. Physiol. Opt. 1997 17: No 2
The measurement of contrast sensitivity in the presence of external visual noise allows any change in the detectability of a signal to be attributed to a change in sampling efficiency, or equivalent noise level, or both. Sampling efficiency indicates the efficiency by which the visual system is able to utilize the available stimulus information. The equivalent noise level gives a measure of the random background noise within the visual system. The aim of the study is to investigate whether binocular summation is due to a change in sampling efficiency or equivalent noise. Contrast detection in noise functions were measured in ten young normal adults under binocular and monocular viewing conditions. Sampling efficiency and equivalent noise levels were computed from the data. Results showed that sampling efficiency increased and equivalent noise decreased under binocular viewing compared to monocular. The existing theories of binocular summation are discussed.
Lectin analysis of endothelial glycoconjugates in the retina of the rat A. J. Hayes’, J. G. Lawrenson and G. Allt2 ‘Applied Vision Research Centre, Department of Optometry and Visual Science, City University, London, UK; ‘Reta Lila Western Institute of Neurological Studies, University College London Medical School, London, UK The vascular endothelial glycocalyx has many important functions such as mediating cell-cell interactions and possibly a role in permeability. The aim of this study was to investigate the expression of endothelial cell (EC) glycoconjugates in retinal microvessels. Paraffin sections of fixed adult rat retina were treated with a range of biotinylated lectins followed by an avidin-FITC conjugate. Binding sites for the lectins Cunavalia ensiformis (Con A), Ricinus communis (RCA) and Triticum vulgaris (WGA) were expressed Sambicus nigra (SNA), which labels terminal sialic acid residues (NeuNAc) in a 2-6 glycosidic linkage to /3 galactose (PGal), and Maakia amurensis (MAA), which labels terminal sialic acid when joined in a 2-3 linkage to p galactose, both labelled strongly. In contrast, Ulex europaeus (UEA) and Glycine VIM (SBA) were negative Arachis hypogaea (PNA). which labels the terminal disaccharide sequence galactose 0 l-3 N-acetylgalactosamine (GalNAc), was strongly positive only after pre-treatment with the sialic acid digesting enzyme neuraminidase. These suggest a predominance of the oligosaccharide sequence: NeuNAc a 2-3 Gal /3 l-3 GalNAc and NeuNAc 012-6 Gal fl l-3 Gal. These sugar sequences may be significant in the function of the glycocalyx in retinal microvessels. Acknowledgement: Supported by the Nuffield Foundation.
Early detection of changes in visual function in diabetes mellitus G. M. Ismail and D. Whitaker Department of Optometry, University of Bradford, Richmond Road, Bradford BD7 lDP, UK Purpose: Several measures of visual performance were used to investigate the possibility of a reliable. quick and low-cost method of differentiating between diabetic patients with and without early retinopathy. Methods: Four groups of patients were recruited: a normal control group (30 patients); a non-insulin dependent diabetic group without retinopathy (30 patients): a similar group with early retinopathy (30 patients); a similar group with more advanced retinopathy (14 patients). High- and lowcontrast LogMAR visual acuity, Pelli-Robson contrast sensitivity and the Farnsworth-Munsell loo-Hue colour vision test were performed on all patients by an experimenter who was independent of the classification stage. Results: Comparison of mean test scores for each subject group reveals deficits in performance for all tests as a function of severity of diabetic retinal changes. However, none of the tests were successful in differentiating the subject groups with and without early retinopathy (P >> 0.05). Larger differences in performance were found when comparing the
non-diabetics against diabetics without retinopathy. Both the Pelli-Robson chart and the lOO-Hue test result in mean scores which were significantly different in these two groups (P < 0.01 and P < 0.05 respectively). QROC analysis of the results confirmed this impression, with kappa coefficients for efficiency of discriminability being generally higher for comparison between non-diabetics and those without retinopathy (0.17 < K < 0.37) than between early diabetic groups (0. I3 < K < 0.26). Discrimination between patients with pre-clinical diabetics and those with moderate retinopathy was more efficient (0.21 < K < 0.62). Conclusion: Tests of visual function appear to be of limited value in screening for the presence of early retinopathy. Rather, a mild decline in visual function appears to already be present in those diabetics without retinopathy.
Age-related changes in central and peripheral contrast sensitivity Keziah Latham, Ian Ferguson and Ian Pacey Department of Vision Sciences, Aston University, Birmingham B4 7ET, UK Purpose: Loss of fovea1 contrast sensitivity at mid-high spatial frequencies with increasing age is well documented. The effects of increasing age on peripheral vision are less clear. This study examines the relative effects of age on contrast sensitivity at the fovea and in the periphery, using scaled 2D Gabor patches. Methods: Five young (age 23.4 f 2.4 yrs) and five elderly (age 71.9 i 3.4yrs) visually normal subjects participated. Stimuli were a series of size-scaled Gabor patches, each consisting of a constant 0.8 grating cycles per envelope standard deviation. To achieve this, Gaussian envelope size varied inversely with the spatial frequency of the carrier grating. Stimuli were presented at 0” and 10” eccentricity in nasal visual field. Contrast sensitivity was measured using a staircase procedure which converged to a performance level of 79% correct. The subject’s task was to correctly identify grating orientation as vertical or horizontal. Results: For both the young and elderly subjects, contrast sensitivity functions at the two eccentricities are displaced from one another simply by a change in size scale. E, values, describing the rate of scale change with eccentricity, are 5.8” for young and 8. lo for elderly observers. At the fovea, the elderly show a 0.29 log unit sensitivity loss relative to the young, independent of spatial frequency. At 10” eccentricity, the agerelated loss is 0.19 log units. Inclusion of a 0.5 log unit neutral density filter reduces the sensitivity of young observers by 0.09 log units at the fovea and 0.07 log units at 10”. Conclusion: Age-related contrast sensitivity loss occurs predominantly at the fovea. Only part of the loss observed can be attributed to optical factors. Contrast sensitivity is qualitatively the same in the fovea and periphery of young and elderly observers. The only variables affecting the quantitative variations are a scale change dependent on both eccentricity and age, and an age-related sensitivity loss.
Spatiotopic cues enhance the dynamic accommodation response profile Helena M. Culhane, Barry Winn and Niall C. Strang Department of Optometry, University of Bradford, Bradford BD7 IDP, UK Purpose: To determine the influence of optically-induced and real changes in stimulus vergence on the profile of the accommodation response. Method: Accommodation was measured on 8 visually normal subjects (mean age 25.6 k6.0 years) using a dynamic tracking infra-red optometer. A Badal stimulus optometer was used to induce optical changes in stimulus vergence which eliminated spatiotopic cues. Targets were also located in real space to provide both retinotopic and spatiotopic cues. Step changes in stimulus vergence were modulated over a 2 D (2-4 D) range for both conditions. Data were collected at a sampling rate of 102.4Hz using a digital storage oscilloscope which was interfaced to an IBM PC. Results: Mean responses are presented below.
Ophthal. Physiol. Opt. 1997 17: No 2
The measurement of contrast sensitivity in the presence of external visual noise allows any change in the detectability of a signal to be attributed to a change in sampling efficiency, or equivalent noise level, or both. Sampling efficiency indicates the efficiency by which the visual system is able to utilize the available stimulus information. The equivalent noise level gives a measure of the random background noise within the visual system. The aim of the study is to investigate whether binocular summation is due to a change in sampling efficiency or equivalent noise. Contrast detection in noise functions were measured in ten young normal adults under binocular and monocular viewing conditions. Sampling efficiency and equivalent noise levels were computed from the data. Results showed that sampling efficiency increased and equivalent noise decreased under binocular viewing compared to monocular. The existing theories of binocular summation are discussed.
Lectin analysis of endothelial glycoconjugates in the retina of the rat A. J. Hayes’, J. G. Lawrenson and G. Allt2 ‘Applied Vision Research Centre, Department of Optometry and Visual Science, City University, London, UK; ‘Reta Lila Western Institute of Neurological Studies, University College London Medical School, London, UK The vascular endothelial glycocalyx has many important functions such as mediating cell-cell interactions and possibly a role in permeability. The aim of this study was to investigate the expression of endothelial cell (EC) glycoconjugates in retinal microvessels. Paraffin sections of fixed adult rat retina were treated with a range of biotinylated lectins followed by an avidin-FITC conjugate. Binding sites for the lectins Cunavalia ensiformis (Con A), Ricinus communis (RCA) and Triticum vulgaris (WGA) were expressed Sambicus nigra (SNA), which labels terminal sialic acid residues (NeuNAc) in a 2-6 glycosidic linkage to /3 galactose (PGal), and Maakia amurensis (MAA), which labels terminal sialic acid when joined in a 2-3 linkage to p galactose, both labelled strongly. In contrast, Ulex europaeus (UEA) and Glycine VIM (SBA) were negative Arachis hypogaea (PNA). which labels the terminal disaccharide sequence galactose 0 l-3 N-acetylgalactosamine (GalNAc), was strongly positive only after pre-treatment with the sialic acid digesting enzyme neuraminidase. These suggest a predominance of the oligosaccharide sequence: NeuNAc a 2-3 Gal /3 l-3 GalNAc and NeuNAc 012-6 Gal fl l-3 Gal. These sugar sequences may be significant in the function of the glycocalyx in retinal microvessels. Acknowledgement: Supported by the Nuffield Foundation.
Early detection of changes in visual function in diabetes mellitus G. M. Ismail and D. Whitaker Department of Optometry, University of Bradford, Richmond Road, Bradford BD7 lDP, UK Purpose: Several measures of visual performance were used to investigate the possibility of a reliable. quick and low-cost method of differentiating between diabetic patients with and without early retinopathy. Methods: Four groups of patients were recruited: a normal control group (30 patients); a non-insulin dependent diabetic group without retinopathy (30 patients): a similar group with early retinopathy (30 patients); a similar group with more advanced retinopathy (14 patients). High- and lowcontrast LogMAR visual acuity, Pelli-Robson contrast sensitivity and the Farnsworth-Munsell loo-Hue colour vision test were performed on all patients by an experimenter who was independent of the classification stage. Results: Comparison of mean test scores for each subject group reveals deficits in performance for all tests as a function of severity of diabetic retinal changes. However, none of the tests were successful in differentiating the subject groups with and without early retinopathy (P >> 0.05). Larger differences in performance were found when comparing the
non-diabetics against diabetics without retinopathy. Both the Pelli-Robson chart and the lOO-Hue test result in mean scores which were significantly different in these two groups (P < 0.01 and P < 0.05 respectively). QROC analysis of the results confirmed this impression, with kappa coefficients for efficiency of discriminability being generally higher for comparison between non-diabetics and those without retinopathy (0.17 < K < 0.37) than between early diabetic groups (0. I3 < K < 0.26). Discrimination between patients with pre-clinical diabetics and those with moderate retinopathy was more efficient (0.21 < K < 0.62). Conclusion: Tests of visual function appear to be of limited value in screening for the presence of early retinopathy. Rather, a mild decline in visual function appears to already be present in those diabetics without retinopathy.
Age-related changes in central and peripheral contrast sensitivity Keziah Latham, Ian Ferguson and Ian Pacey Department of Vision Sciences, Aston University, Birmingham B4 7ET, UK Purpose: Loss of fovea1 contrast sensitivity at mid-high spatial frequencies with increasing age is well documented. The effects of increasing age on peripheral vision are less clear. This study examines the relative effects of age on contrast sensitivity at the fovea and in the periphery, using scaled 2D Gabor patches. Methods: Five young (age 23.4 f 2.4 yrs) and five elderly (age 71.9 i 3.4yrs) visually normal subjects participated. Stimuli were a series of size-scaled Gabor patches, each consisting of a constant 0.8 grating cycles per envelope standard deviation. To achieve this, Gaussian envelope size varied inversely with the spatial frequency of the carrier grating. Stimuli were presented at 0” and 10” eccentricity in nasal visual field. Contrast sensitivity was measured using a staircase procedure which converged to a performance level of 79% correct. The subject’s task was to correctly identify grating orientation as vertical or horizontal. Results: For both the young and elderly subjects, contrast sensitivity functions at the two eccentricities are displaced from one another simply by a change in size scale. E, values, describing the rate of scale change with eccentricity, are 5.8” for young and 8. lo for elderly observers. At the fovea, the elderly show a 0.29 log unit sensitivity loss relative to the young, independent of spatial frequency. At 10” eccentricity, the agerelated loss is 0.19 log units. Inclusion of a 0.5 log unit neutral density filter reduces the sensitivity of young observers by 0.09 log units at the fovea and 0.07 log units at 10”. Conclusion: Age-related contrast sensitivity loss occurs predominantly at the fovea. Only part of the loss observed can be attributed to optical factors. Contrast sensitivity is qualitatively the same in the fovea and periphery of young and elderly observers. The only variables affecting the quantitative variations are a scale change dependent on both eccentricity and age, and an age-related sensitivity loss.
Spatiotopic cues enhance the dynamic accommodation response profile Helena M. Culhane, Barry Winn and Niall C. Strang Department of Optometry, University of Bradford, Bradford BD7 IDP, UK Purpose: To determine the influence of optically-induced and real changes in stimulus vergence on the profile of the accommodation response. Method: Accommodation was measured on 8 visually normal subjects (mean age 25.6 k6.0 years) using a dynamic tracking infra-red optometer. A Badal stimulus optometer was used to induce optical changes in stimulus vergence which eliminated spatiotopic cues. Targets were also located in real space to provide both retinotopic and spatiotopic cues. Step changes in stimulus vergence were modulated over a 2 D (2-4 D) range for both conditions. Data were collected at a sampling rate of 102.4Hz using a digital storage oscilloscope which was interfaced to an IBM PC. Results: Mean responses are presented below.