- Email: [email protected]
Prevalence of significant pre-clinical contrast sensitivity loss in diabetics
170
Ophthal. Physiol. Opt. 1997 17: No 2
neither wore CL and other recognized factors were absent. Conclusions: Predisposing factors in culture-positive CI were CL wear and previous HSV keratitis. Compliant use of hydrogen peroxide disinfection in CL wearers was not associated with culture-positive infiltration.
Effects of age-related cataract on obstacle avoidance strategies D. B. Elliot’, A. E. Patla2, A. L. Adkin’ and M. Furniss3 ‘Department of Optometry, University of Bradford, UK; 2Department of Kinesiology, University of Waterloo, Canada; ‘School of Optometry, University of Waterloo, Canada Purpose: To examine the effects of age-related cataract on obstacle avoidance strategies. A key health issue facing the elderly population is an increase in the incidence of falls, which can be attributed to tripping over obstacles. Methods: Subjects with age-related cataract (n = 9; 75.2 f 4.7 years; 1.71 rf- 0.07 m height) and normal, healthy eyes (n = 23; 72.5 k 4.3 years; 1.71 f 0.09 m height) were recruited. Subjects were required to repeatedly walk a straight path and step over one of two low contrast foam obstacles (6.7cm and 26.8cm high). Detailed locomotor changes were assessed using four infra-red diodes affixed to the various points on the subject’s lower limbs and the OPTOTRAK motion analysis system. Results: Cataract subjects had an increased incidence of tripping with both the leading (3.2 vs. 0%) and trailing limbs (4.0 vs. 0.7%). Lead limb toe clearance was higher ( - 19 vs. 15 cm) and horizontal toe velocity lower ( _ 2.5 vs. 3.0 misec) in the cataract subjects compared to the controls. Conclusions: Cataract patients adapted their obstacle avoidance strategies in order to minimize the chances of tripping. However, significantly greater occurrences of tripping still occurred. We hope to present additional post-surgery and second eye surgery data. Supported by Health and Welfare (Canada) grant #6606-5351-402.
Prevalence of significant pre-clinical contrast sensitivity loss in diabetics Jim Gilchrist’, Richard Pope’, Usha Dhanesha3, Sally Young’ and Clare Horsley’ ‘Department of Optometry, University of Bradford, West Yorkshire; 2Airedale General Hospital, Steeton, West Yorkshire; 3Coventry and Warwickshire Hospital, Coventry, West Midlands, UK Aim: To estimate the prevalence of impaired contrast sensitivity (CS) in diabetic patients with normal visual acuity and no clinical detectable retinopathy Methods: We measured CS in 75 diabetics with visual acuity of logMAR 0.0 or better, no evidence of retinopathy by direct ophthalmoscopy and fundus photography, and no evidence of cataract. The sample comprised 27 IDDM (15-44 years), and 48 NIDDM (35-71 years). The CS of each patient was measured with sinusoidal gratings at 2, 4 and 8 cdeg-’ using a two-alternative forced-choice staircase procedure, and the data were compared with CS values from age-related non-diabetic patients. A decision was made for each diabetic that CS was either normal or impaired, based on whether that individual’s CS fell more than 2 standard deviations (Criterion A) or 3 standard deviations (Criterion B) below the age-related non-diabetic mean value. Results and conclusions: Estimated proportions, averaged across all spatial frequencies, of diabetic patients with impaired CS were: 28% by Criterion A and 15% by Criterion B. Population estimates (95% confidence intervals) for the prevalence of significant pre-clinical CS loss in diabetics based on these results are: 18-38% using Criterion A and 7-23% using Criterion B.
Use of visual evoked potentials (VEPs) to investigate mechanisms involved in the reading process J. C. Greatrex and N. Drasdo Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 90.5, Cardiff CFl 3XF, UK Aim: In this study we have attempted to use VEPs directly to investigate visual mechanisms in the initial stages of the reading process. Method: The pattern onset mode of stimulation (using a 330ms presentation time) approximately stimulates the intake of information during reading and accordingly we have adopted this technique to investigate possible responses at several cortical loci which are known to be involved in the reading process. To obtain the best results from localized areas of the cortex, a technique using a 3 cm radius triangular Laplacian derivation was adapted. Right and left hemifoveal responses were recorded with a Medelec Sapphire system, using pattern and letter stimuli. Signals arising from two putative generators, one in the striate cortex (5 % up from inion, on the midline) and another possibly from the human homologue of primate area V4 (12.5% up from inion, 17% right), were studied using the 1-3” stimuli to determine contrast responses and spatial selectivity. Four averaged responses from 32 sweeps, filtered (l-50 Hz), were recorded for contrasts of 80% and 20% and spatial frequencies between l-22.32 cpd. Results: The tuning function for checkerboard patterns at 80% contrast for the lateral generator peaked at 2.75 cpd and showed a rapid fall off. The midline response at 80% contrast peaked at 5 cpd and showed a much slower fall off. Responses to letter stimuli were attenuated to approximately 1 FV over V4 and 300 nanovolts from the angularisupramarginal gyri. No significant result was obtained from Wemicke’s and Broca’s areas. Conclusions: VEPs may be used to directly investigate the reading process. Further refinement of techniques is necessary to record responses from more specialized areas such as Wernicke’s and Broca’s areas.
Intracellular chloride activity in cornea1 endothelial cells Helen C. Turner, Chris G. Wigham and Stuart A. Hodson Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF, UK Purpose: Current models of hydration control by the cornea1 endothelium suggest that HCO; movement across the cell is driven by the energy contained in the re-entry of NA+ into the cell down its electrochemical gradient. The nature of the coupling between HCO; and Na+ is not yet fully resolved. One suggestion is that the Na+/K+I2Clco-transporter drives Cl- into the cell which then exits the same membrane via a HCO,/Cl- exchanger. This would drive HCO; into the cell from where it could exit down its own electrochemical gradient into the aqueous. Such a system would also raise Cl- above its electrochemical equilibrium. The purpose of this study was to determine if Cl- is passively distributed across the plasma membrane or elevated above its electrochemical equilibrium. Method: To determine if this situation was present in rabbit cornea1 endothelial cells, we measured [Cl-] , directly using potential sensing and Cl- selective microelectrodes. To make the Cl- selective microelectrodes, filamented glass capillaries were silanized and back-filled with Cl- ionophore (Corning or WPI) immediately before use. Electrode sensitivity was determined using the fixed interference method. Results: Endothelial membrane potential (PD,) in this series was similar to that in previous studies, 29 + 0.9 mV (mean + SEM, n = 22). Chloride potential (PD,,) was used to calculate [Cl-] ;, which was 53 f 2.0 mM (mean * SEM, n = 22). Conclusions: The [Cl-] I measurement is significantly higher (P < 0.001) than that predicted from the measured PD, (39 i- 0.9 mM) and suggests that Cl- is not passively distributed in cornea1 endothelial cells.
Patterns in cataract referral: room for improvement? Keziah L&am’ and Gary Misson ‘Department of Vision Sciences, Aston University, Birmingham; and 2Solihull Hospital and Birmingham & Midland Eye Centre, Birmingham, UK
Ophthal. Physiol. Opt. 1997 17: No 2
neither wore CL and other recognized factors were absent. Conclusions: Predisposing factors in culture-positive CI were CL wear and previous HSV keratitis. Compliant use of hydrogen peroxide disinfection in CL wearers was not associated with culture-positive infiltration.
Effects of age-related cataract on obstacle avoidance strategies D. B. Elliot’, A. E. Patla2, A. L. Adkin’ and M. Furniss3 ‘Department of Optometry, University of Bradford, UK; 2Department of Kinesiology, University of Waterloo, Canada; ‘School of Optometry, University of Waterloo, Canada Purpose: To examine the effects of age-related cataract on obstacle avoidance strategies. A key health issue facing the elderly population is an increase in the incidence of falls, which can be attributed to tripping over obstacles. Methods: Subjects with age-related cataract (n = 9; 75.2 f 4.7 years; 1.71 rf- 0.07 m height) and normal, healthy eyes (n = 23; 72.5 k 4.3 years; 1.71 f 0.09 m height) were recruited. Subjects were required to repeatedly walk a straight path and step over one of two low contrast foam obstacles (6.7cm and 26.8cm high). Detailed locomotor changes were assessed using four infra-red diodes affixed to the various points on the subject’s lower limbs and the OPTOTRAK motion analysis system. Results: Cataract subjects had an increased incidence of tripping with both the leading (3.2 vs. 0%) and trailing limbs (4.0 vs. 0.7%). Lead limb toe clearance was higher ( - 19 vs. 15 cm) and horizontal toe velocity lower ( _ 2.5 vs. 3.0 misec) in the cataract subjects compared to the controls. Conclusions: Cataract patients adapted their obstacle avoidance strategies in order to minimize the chances of tripping. However, significantly greater occurrences of tripping still occurred. We hope to present additional post-surgery and second eye surgery data. Supported by Health and Welfare (Canada) grant #6606-5351-402.
Prevalence of significant pre-clinical contrast sensitivity loss in diabetics Jim Gilchrist’, Richard Pope’, Usha Dhanesha3, Sally Young’ and Clare Horsley’ ‘Department of Optometry, University of Bradford, West Yorkshire; 2Airedale General Hospital, Steeton, West Yorkshire; 3Coventry and Warwickshire Hospital, Coventry, West Midlands, UK Aim: To estimate the prevalence of impaired contrast sensitivity (CS) in diabetic patients with normal visual acuity and no clinical detectable retinopathy Methods: We measured CS in 75 diabetics with visual acuity of logMAR 0.0 or better, no evidence of retinopathy by direct ophthalmoscopy and fundus photography, and no evidence of cataract. The sample comprised 27 IDDM (15-44 years), and 48 NIDDM (35-71 years). The CS of each patient was measured with sinusoidal gratings at 2, 4 and 8 cdeg-’ using a two-alternative forced-choice staircase procedure, and the data were compared with CS values from age-related non-diabetic patients. A decision was made for each diabetic that CS was either normal or impaired, based on whether that individual’s CS fell more than 2 standard deviations (Criterion A) or 3 standard deviations (Criterion B) below the age-related non-diabetic mean value. Results and conclusions: Estimated proportions, averaged across all spatial frequencies, of diabetic patients with impaired CS were: 28% by Criterion A and 15% by Criterion B. Population estimates (95% confidence intervals) for the prevalence of significant pre-clinical CS loss in diabetics based on these results are: 18-38% using Criterion A and 7-23% using Criterion B.
Use of visual evoked potentials (VEPs) to investigate mechanisms involved in the reading process J. C. Greatrex and N. Drasdo Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 90.5, Cardiff CFl 3XF, UK Aim: In this study we have attempted to use VEPs directly to investigate visual mechanisms in the initial stages of the reading process. Method: The pattern onset mode of stimulation (using a 330ms presentation time) approximately stimulates the intake of information during reading and accordingly we have adopted this technique to investigate possible responses at several cortical loci which are known to be involved in the reading process. To obtain the best results from localized areas of the cortex, a technique using a 3 cm radius triangular Laplacian derivation was adapted. Right and left hemifoveal responses were recorded with a Medelec Sapphire system, using pattern and letter stimuli. Signals arising from two putative generators, one in the striate cortex (5 % up from inion, on the midline) and another possibly from the human homologue of primate area V4 (12.5% up from inion, 17% right), were studied using the 1-3” stimuli to determine contrast responses and spatial selectivity. Four averaged responses from 32 sweeps, filtered (l-50 Hz), were recorded for contrasts of 80% and 20% and spatial frequencies between l-22.32 cpd. Results: The tuning function for checkerboard patterns at 80% contrast for the lateral generator peaked at 2.75 cpd and showed a rapid fall off. The midline response at 80% contrast peaked at 5 cpd and showed a much slower fall off. Responses to letter stimuli were attenuated to approximately 1 FV over V4 and 300 nanovolts from the angularisupramarginal gyri. No significant result was obtained from Wemicke’s and Broca’s areas. Conclusions: VEPs may be used to directly investigate the reading process. Further refinement of techniques is necessary to record responses from more specialized areas such as Wernicke’s and Broca’s areas.
Intracellular chloride activity in cornea1 endothelial cells Helen C. Turner, Chris G. Wigham and Stuart A. Hodson Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF, UK Purpose: Current models of hydration control by the cornea1 endothelium suggest that HCO; movement across the cell is driven by the energy contained in the re-entry of NA+ into the cell down its electrochemical gradient. The nature of the coupling between HCO; and Na+ is not yet fully resolved. One suggestion is that the Na+/K+I2Clco-transporter drives Cl- into the cell which then exits the same membrane via a HCO,/Cl- exchanger. This would drive HCO; into the cell from where it could exit down its own electrochemical gradient into the aqueous. Such a system would also raise Cl- above its electrochemical equilibrium. The purpose of this study was to determine if Cl- is passively distributed across the plasma membrane or elevated above its electrochemical equilibrium. Method: To determine if this situation was present in rabbit cornea1 endothelial cells, we measured [Cl-] , directly using potential sensing and Cl- selective microelectrodes. To make the Cl- selective microelectrodes, filamented glass capillaries were silanized and back-filled with Cl- ionophore (Corning or WPI) immediately before use. Electrode sensitivity was determined using the fixed interference method. Results: Endothelial membrane potential (PD,) in this series was similar to that in previous studies, 29 + 0.9 mV (mean + SEM, n = 22). Chloride potential (PD,,) was used to calculate [Cl-] ;, which was 53 f 2.0 mM (mean * SEM, n = 22). Conclusions: The [Cl-] I measurement is significantly higher (P < 0.001) than that predicted from the measured PD, (39 i- 0.9 mM) and suggests that Cl- is not passively distributed in cornea1 endothelial cells.
Patterns in cataract referral: room for improvement? Keziah L&am’ and Gary Misson ‘Department of Vision Sciences, Aston University, Birmingham; and 2Solihull Hospital and Birmingham & Midland Eye Centre, Birmingham, UK