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The measurement of sampling efficiency and equivalent noise levels in binocular and monocular viewing conditions
Abstracts Method: 13 1 patients were recruited from the diabetic clinics at Airedale General Hospital. Those with proliferative DR or cataract were excluded from the study. Blood pressure was measured at rest and the measurements of plasma glucose, glycosylated haemoglobin and microalbuminuria were taken. Fundus photography was used to classify the extent of DR and ophthalmoscopic examination of the macula was performed. Visual function assessments included the measurement of refractive error, logMAR visual acuity, contrast sensitivity using gratings at three spatial frequencies and the Pelli-Robson letter chart and hue discrimination using the Arden Colour Contrast Sensitivity apparatus. An assessment of the relationship between the metabolic indices and visual function was performed using the Kendall Tau Correlation Test. Results and conclusions: The only meaningful correlation between a clinical optometric test and a metabolic parameter was between refractive error and glycosylated haemoglobin levels (P < 0.05). As HBAlC levels increased refractive error tended towards myopia. The normal hypermetropic shift with age was observed. Rx changes may be indicative of poor long-term metabolic control. There were little/no associations between any other renal, metabolic, haematological or visual parameters contrary to other studies. This may be due to the strict exclusion criteria.
The effect of eccentricity on simultaneous performance in position and movement acuity tasks Pia Miikelii’ , Jyrki Rovamo’ and David Whitaker2 ‘Department of Optometry and Vison Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF; 2Department of Optometry, University of Bradford, Richmond Road, Bradford BD7 lDP, UK Visual performance can be made equal across the visual field in various tasks simply by an appropriate change of scale, but the speed at which performance declines towards periphery varies greatly between tasks. E, denotes the eccentricity at which fovea1 stimulus size must double in order to maintain performance equivalent to that at the fovea. Two tasks, spatial interval discrimination and displacement detection, were presented at the same location to see how simultaneous processing of these two tasks with different E? values would influence eccentricity dependence in each task. The subject was to solve only the spatial interval task, only the displacement task, or both tasks simultaneously. Eccentricity dependence in each condition was determined by using the method of partial scaling, where thresholds were estimated at several eccentricities for a series of stimuli, all of which were simply magnified or minified versions of one another. With 500 msec stimulus duration, the individual E, value was found to be 0.17-0.39” for spatial interval discrimination and 1.0-1.2” for displacement detection. The values remained unaffected whether the subject solved one task or two tasks simultaneously. This finding was confirmed with a 50msec stimulus duration. As there is no interference between tasks, the mechanisms solving the tasks appear to be functionally dependent, i.e. operating in parallel at all eccentricities.
A new contrast sensitivity test for young children-The Cardiff Contrast Test Rahim Barbareza, Margaret Woodhouse and Kola Oduwaiye Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF, UK We have developed a new contrast sensitivity (CS) test (similar in design to the Cardiff Acuity test) for use with children aged from l-3 years. It consists of a set of 42 multi-orientational pictures all of one target size (car, boat, fish, house: train and duck) at 14 contrast levels (3 cards at each level) Results from tests performed on 23 adults (aged from 15-44 years) gave contrast sensitivity measurements in agreement with measurements made using the Pelli-Robson Letter Chart. We tested 138 visually normal children (between 12-66 months) monocularly and binocularly to establish norms. The results from the children indicate that CS increases
175
up to approximately 2 years of age after which it attains adult values. These results suggest that the Cardiff Contrast Test provides an effective measurement technique for the determination of contrast sensitivity in infants.
Dual mechanisms of curvature detection J. A. Davies, P. V. McGraw and D. Whitaker Department of Optometry, University of Bradford, Richmond Road, Bradford BD7 lDP, UK Purpose: The detection of object curvature is an essential feature of human spatial vision. We investigate the combined effects of contrast and blur on thresholds for curvature detection. Methods: Horizontally-oriented line stimuli were displayed on a Macintosh monitor. The lines were windowed in both X- and y-dimensions with a Gaussian profile. We examined a range of x- and y-blur levels by varying the space constant of the relevant Gaussian window, such that stimuli varied in appearance from long, thin lines, to short fat ones. The maximum contrast of the lines varied between 12.5-100%. Subjects were required to indicate whether the line (presented for a duration of 250 msec) was curved upwards or downwards. A method of constant stimuli was used to determine curvature thresholds. Results: At each level of blur (y-space constant), threshold remained constant up to a certain line length (x-space constant) after which they increased. Thresholds also increased with increasing levels of blur. However, performance in all conditions became identical once thresholds were expressed in Weber terms (as a multiple of line length) and stimulus size was specified using a scale-invariant metric (ratio of line length to blur). When line length is small relative to blur (short, fat lines), thresholds are proportional to blur and are contrast dependent. When line length is large relative to blur (long, thin lines), thresholds become proportional to line length and demonstrate reduced contrast-dependence. Conclusion: Combined manipulation of blur and contrast reveals two distinct processes involved in curvature in human vision. Acknowledgements: Supported by the Visual Research Trust and a Wellcome Trust Vacation Scholarship to JAD.
Assessment of time-dependent inter-relationships between spontaneous eyeblink frequency, average and dominant interblink intervals in man Mohammed L. Zaman and Michael J. Doughty Department of Vision Sciences, Glasgow-Caledonian University, Glasgow G4 OBA, Scotland, UK Measures of spontaneous eyeblink activity, despite often being measured, have not been standardized and the reliability of the measures has received very little attention, Video recordings were made of 22 healthy volunteers aged 20 to 58 years, while silently fixating on a 2 m distant, 35 mm high target under 350 lux illumination. Using an event marker, significant fluctuations (up to +35%) in spontaneous eyeblink frequency (SEBF) or inter-blink intervals (IBI) were observed in most subjects, on a minute-byminute basis, over a 5-minute period. However, the eyeblink activity did not conform to a minute-by-minute periodicity and time-dependent trends were uncommon. For subjects < 40 years of age, correlation’s between SEBF and IBI indicated that 3-5 minute assessments were likely to be adequate, but that at least 5 min periods are generally required for older patients. Modal IBI values correlated well with an adjusted modal calculated SEBF and represent a more accurate estimate of the dominant eyelid activity. Methods have thus been standardized to allow meaningful measures of spontaneous eyeblink activity to be made in health and disease.
The measurement of sampling efficiency and equivalent noise levels in binocular and monocular viewing conditions Shahina Pardhan, David Rose and Jim Gilchrist Department of Optometry, University of Bradford, Richmond Road, Bradford BD7 lDP, UK
176
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.
The effect of eccentricity on simultaneous performance in position and movement acuity tasks Pia Miikelii’ , Jyrki Rovamo’ and David Whitaker2 ‘Department of Optometry and Vison Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF; 2Department of Optometry, University of Bradford, Richmond Road, Bradford BD7 lDP, UK Visual performance can be made equal across the visual field in various tasks simply by an appropriate change of scale, but the speed at which performance declines towards periphery varies greatly between tasks. E, denotes the eccentricity at which fovea1 stimulus size must double in order to maintain performance equivalent to that at the fovea. Two tasks, spatial interval discrimination and displacement detection, were presented at the same location to see how simultaneous processing of these two tasks with different E? values would influence eccentricity dependence in each task. The subject was to solve only the spatial interval task, only the displacement task, or both tasks simultaneously. Eccentricity dependence in each condition was determined by using the method of partial scaling, where thresholds were estimated at several eccentricities for a series of stimuli, all of which were simply magnified or minified versions of one another. With 500 msec stimulus duration, the individual E, value was found to be 0.17-0.39” for spatial interval discrimination and 1.0-1.2” for displacement detection. The values remained unaffected whether the subject solved one task or two tasks simultaneously. This finding was confirmed with a 50msec stimulus duration. As there is no interference between tasks, the mechanisms solving the tasks appear to be functionally dependent, i.e. operating in parallel at all eccentricities.
A new contrast sensitivity test for young children-The Cardiff Contrast Test Rahim Barbareza, Margaret Woodhouse and Kola Oduwaiye Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF, UK We have developed a new contrast sensitivity (CS) test (similar in design to the Cardiff Acuity test) for use with children aged from l-3 years. It consists of a set of 42 multi-orientational pictures all of one target size (car, boat, fish, house: train and duck) at 14 contrast levels (3 cards at each level) Results from tests performed on 23 adults (aged from 15-44 years) gave contrast sensitivity measurements in agreement with measurements made using the Pelli-Robson Letter Chart. We tested 138 visually normal children (between 12-66 months) monocularly and binocularly to establish norms. The results from the children indicate that CS increases
175
up to approximately 2 years of age after which it attains adult values. These results suggest that the Cardiff Contrast Test provides an effective measurement technique for the determination of contrast sensitivity in infants.
Dual mechanisms of curvature detection J. A. Davies, P. V. McGraw and D. Whitaker Department of Optometry, University of Bradford, Richmond Road, Bradford BD7 lDP, UK Purpose: The detection of object curvature is an essential feature of human spatial vision. We investigate the combined effects of contrast and blur on thresholds for curvature detection. Methods: Horizontally-oriented line stimuli were displayed on a Macintosh monitor. The lines were windowed in both X- and y-dimensions with a Gaussian profile. We examined a range of x- and y-blur levels by varying the space constant of the relevant Gaussian window, such that stimuli varied in appearance from long, thin lines, to short fat ones. The maximum contrast of the lines varied between 12.5-100%. Subjects were required to indicate whether the line (presented for a duration of 250 msec) was curved upwards or downwards. A method of constant stimuli was used to determine curvature thresholds. Results: At each level of blur (y-space constant), threshold remained constant up to a certain line length (x-space constant) after which they increased. Thresholds also increased with increasing levels of blur. However, performance in all conditions became identical once thresholds were expressed in Weber terms (as a multiple of line length) and stimulus size was specified using a scale-invariant metric (ratio of line length to blur). When line length is small relative to blur (short, fat lines), thresholds are proportional to blur and are contrast dependent. When line length is large relative to blur (long, thin lines), thresholds become proportional to line length and demonstrate reduced contrast-dependence. Conclusion: Combined manipulation of blur and contrast reveals two distinct processes involved in curvature in human vision. Acknowledgements: Supported by the Visual Research Trust and a Wellcome Trust Vacation Scholarship to JAD.
Assessment of time-dependent inter-relationships between spontaneous eyeblink frequency, average and dominant interblink intervals in man Mohammed L. Zaman and Michael J. Doughty Department of Vision Sciences, Glasgow-Caledonian University, Glasgow G4 OBA, Scotland, UK Measures of spontaneous eyeblink activity, despite often being measured, have not been standardized and the reliability of the measures has received very little attention, Video recordings were made of 22 healthy volunteers aged 20 to 58 years, while silently fixating on a 2 m distant, 35 mm high target under 350 lux illumination. Using an event marker, significant fluctuations (up to +35%) in spontaneous eyeblink frequency (SEBF) or inter-blink intervals (IBI) were observed in most subjects, on a minute-byminute basis, over a 5-minute period. However, the eyeblink activity did not conform to a minute-by-minute periodicity and time-dependent trends were uncommon. For subjects < 40 years of age, correlation’s between SEBF and IBI indicated that 3-5 minute assessments were likely to be adequate, but that at least 5 min periods are generally required for older patients. Modal IBI values correlated well with an adjusted modal calculated SEBF and represent a more accurate estimate of the dominant eyelid activity. Methods have thus been standardized to allow meaningful measures of spontaneous eyeblink activity to be made in health and disease.
The measurement of sampling efficiency and equivalent noise levels in binocular and monocular viewing conditions Shahina Pardhan, David Rose and Jim Gilchrist Department of Optometry, University of Bradford, Richmond Road, Bradford BD7 lDP, UK
176
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.