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Patterns in cataract referral: room for improvement?
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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
Abstracts Purpose: Optometrists are expected to refer patients with any abnormality of the eye excluding normal changes due to age to their general practitioner. It can be difficult to decide when a cataract ceases to be a normal age-related change and becomes an ocular abnormality. This study examines the criteria adopted by optometrists and GPs for referring patients with cataract and compares this to the referral criteria suggested by ophthalmologists. Method: Questionnaires were sent to all optometrists and GPs registered with Birmingham Health Authority and ophthalmologists in the West Midlands area. Questions covered methods of subjective and objective assessment of lens opacities, subjective referral criteria, and views on communications between the three professions. Results: For all professions, the main factors influencing referral are visual acuity, subjective visual impairment and the need to drive. Optometrists and GPs generally refer patients with cataract at a VA level of 6/l&6/24, whilst ophthalmologists would be willing to see patients with cataract at a VA of 6/9-6/12. However, most ophthalmologists report that sometimes patients are referred too soon, regardless of their acuity level, because the patient is not yet impaired by their level of vision or does not want surgery. Conclusion: Suggestions for improvements in the referral of cataract will be discussed. It is important for optometrists to make clear whether a letter to a GP is for information only or referral. If referral is warranted the following information, in addition to acuity, will assist an ophthalmologist in prioritizing appointments: age, occupation, brief description of disability and the need to drive legally. Acknowledgements: Liz Hutchinson, Sarah Caddy and Carrie Buckland for data collection; Dr Richard Armstrong for assistance with statistics.
Quality control measures for slaughterhouse eyes used for ex vivo cornea1 epithelial toxicity assays Michael J. Doughty Department of Vision Sciences, Glasgow-Caledonian University, Glasgow G4 OBA, UK Slaughterhouse animal eyes are widely used in cornea1 toxicological research, yet there are few guidelines on material selection so as to optimize intra- and inter-laboratory comparisons. Using bovine material (Hereford or Holstein) over 18 months from a single slaughterhouse, a wide range of cornea1 thickness (CCT) values were encountered due to differences in eye size (I = 0.917) or post-mortem dessication (I = 0.623). In evaluation of quality selected eyes in the enucleated eye toxicity (EET) protocol, corneas from smaller eyes showed faster and more substantial CCT increase to benzalkonium chloride challenge (Y = 0.629). Corneas with evidence of dessication evaluated by EET or with ex viva cornea1 perfusion also developed more oedema. Evaluation of cornea1 epithrlial cell extracts, and a mitochondrial-lysosomal fraction, revealed significant differences in the activities of hexosaminidase, acid phosphatase, lactate dehydrogenase and leucine arylamidase as related to the quality of the eyes. Lysosomal enzyme latency was especially sensitive to quality of the eyes on receipt, and could be totally eliminated by even 5 min exposure of the cornea1 epitheliai surface ex viva to 0.01% benzalkonium chloride. These types of differences in enzyme activity could underly the marked differences in ex viva responses.
The light scattering characteristics of the eye M. L. Hennelly, J. L. Barbur, D. F. Edgar and E. G. Woodward Department of Optometry and Visual Science, City University, Dame Alice Owen Building, 3 11-321 Goswell Road, London EClV 7DD, UK Aim: To validate a new method for the measurement of scattered light in the eye. In addition, normal values and results of subjects with keratoconus. cataract and cornea1 dystrophy will be demonstrated. Method: The scatter programme is implemented on the P-Scan 100
171
system. The system involves the use of high luminances and extended stimuli modulated sinusoidally. It reveals three parameters; n the scatter index which describes the distribution of scattered light from the scattering source; k, which describes the overall light scattered and a new index k’ known as the integrated straylight parameter. k’ provides an alternative to the commonly used straylight parameter, k. Results: Preliminary results in a small sample of normals showed k’ to be affected by age, diurnally, and by the menstrual cycle. Little variation in k’ was found between the ages of 16 and 42 years, with an increase found after the age of 60. A diurnal variation was found, with increased values of k’ on waking, which may be related to variation in cornea1 thickness. A variation in k’ with the menstrual cycle was noted. All values, i.e. n, k, k’ were found to be affected by keratoconus, cataract and cornea1 dystrophy. Conclusion: k’ is an important parameter in the quantification of scattered light. The results obtained give an insight into the patient’s symptoms of glare, essential in the timing of conducting penetrating keratoplasty. Acknowledgement: M. L. Hennelly was supported by a College of Optometry Studentship.
Increased incidence of Acanthamoeba keratitis associated with contact lens wear: the need to prevent this waterborne infection D. Seal, J. Hay, 0. M. Kirkness and West of Scotland Keratitis Study Group Tennent Institute of Ophthalmology, Western Infirmary, Glasgow Gil 6NT, UK The incidence of Acanfhamoeba keratitis has been assessed in the 1995 West of Scotland Keratitis Study. All patients with microbial keratitis in the 3 million population were reported to us prospectively by optometrists, ophthalmologists and microbiologists. Contact lens (CL) wearing patients completed detailed questionnaires; 50 healthy CL wearers were visited at home as controls and similarly investigated. Additionally all 340 optician practises were polled for their annual turnover of CL types and disinfectant solutions. Acanthamoeba keratitis occurred with an incidence of l/l0000 CL wearers based on this large, reliable community study of 164 000 CL wearers. This is 2.5 times more frequent than the previous American estimate (i.e. 1 :250 000). The relationship to CL material type, ineffective cold chemicals solutions and hygiene compliance is complex, but is directly related to use of contaminated tap water as part of CL care, this vehicle being the source of the amoebae. These findings are of considerable concern. They suggest that many new cases of painful, distressing and potentially blinding infection will be seen in Asia as CL wear becomes more widely available. Local expertise for recognition of Acanrhamoeba keratitis will be required plus treatment with a combination of 0.02% chlorhexidine and 0.1% propamidine. Tap water must be avoided in CL care, and rigorous attention paid to CL hygiene.
Anion binding in bovine cornea1 stroma Douglas H. Kerswell and Stuart A. Hodson Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF, UK Purpose: The cornea1 stroma strives to take up water because of the osmotic gradient created by fixed negative charges within the stroma. This fixed negative charge is known to be partly due to glycosaminoglycans and thought to be partly due to bound Cl- ions in the stroma. This study investigates the presence of anion binding within bovine stroma. Methods: Bovine corneas were isolated, de-epithelialized and deendothelialized. The stromal uptake of NaCl, NaAcetate, NaThiocyanate and NaHCO, solutions at various concentrations was observed using a digital balance. The dry weight of each cornea was noted. Stromal hydrations were calculated and analysed. Results: As the bathing solution concentration increased, for all solutions
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
Abstracts Purpose: Optometrists are expected to refer patients with any abnormality of the eye excluding normal changes due to age to their general practitioner. It can be difficult to decide when a cataract ceases to be a normal age-related change and becomes an ocular abnormality. This study examines the criteria adopted by optometrists and GPs for referring patients with cataract and compares this to the referral criteria suggested by ophthalmologists. Method: Questionnaires were sent to all optometrists and GPs registered with Birmingham Health Authority and ophthalmologists in the West Midlands area. Questions covered methods of subjective and objective assessment of lens opacities, subjective referral criteria, and views on communications between the three professions. Results: For all professions, the main factors influencing referral are visual acuity, subjective visual impairment and the need to drive. Optometrists and GPs generally refer patients with cataract at a VA level of 6/l&6/24, whilst ophthalmologists would be willing to see patients with cataract at a VA of 6/9-6/12. However, most ophthalmologists report that sometimes patients are referred too soon, regardless of their acuity level, because the patient is not yet impaired by their level of vision or does not want surgery. Conclusion: Suggestions for improvements in the referral of cataract will be discussed. It is important for optometrists to make clear whether a letter to a GP is for information only or referral. If referral is warranted the following information, in addition to acuity, will assist an ophthalmologist in prioritizing appointments: age, occupation, brief description of disability and the need to drive legally. Acknowledgements: Liz Hutchinson, Sarah Caddy and Carrie Buckland for data collection; Dr Richard Armstrong for assistance with statistics.
Quality control measures for slaughterhouse eyes used for ex vivo cornea1 epithelial toxicity assays Michael J. Doughty Department of Vision Sciences, Glasgow-Caledonian University, Glasgow G4 OBA, UK Slaughterhouse animal eyes are widely used in cornea1 toxicological research, yet there are few guidelines on material selection so as to optimize intra- and inter-laboratory comparisons. Using bovine material (Hereford or Holstein) over 18 months from a single slaughterhouse, a wide range of cornea1 thickness (CCT) values were encountered due to differences in eye size (I = 0.917) or post-mortem dessication (I = 0.623). In evaluation of quality selected eyes in the enucleated eye toxicity (EET) protocol, corneas from smaller eyes showed faster and more substantial CCT increase to benzalkonium chloride challenge (Y = 0.629). Corneas with evidence of dessication evaluated by EET or with ex viva cornea1 perfusion also developed more oedema. Evaluation of cornea1 epithrlial cell extracts, and a mitochondrial-lysosomal fraction, revealed significant differences in the activities of hexosaminidase, acid phosphatase, lactate dehydrogenase and leucine arylamidase as related to the quality of the eyes. Lysosomal enzyme latency was especially sensitive to quality of the eyes on receipt, and could be totally eliminated by even 5 min exposure of the cornea1 epitheliai surface ex viva to 0.01% benzalkonium chloride. These types of differences in enzyme activity could underly the marked differences in ex viva responses.
The light scattering characteristics of the eye M. L. Hennelly, J. L. Barbur, D. F. Edgar and E. G. Woodward Department of Optometry and Visual Science, City University, Dame Alice Owen Building, 3 11-321 Goswell Road, London EClV 7DD, UK Aim: To validate a new method for the measurement of scattered light in the eye. In addition, normal values and results of subjects with keratoconus. cataract and cornea1 dystrophy will be demonstrated. Method: The scatter programme is implemented on the P-Scan 100
171
system. The system involves the use of high luminances and extended stimuli modulated sinusoidally. It reveals three parameters; n the scatter index which describes the distribution of scattered light from the scattering source; k, which describes the overall light scattered and a new index k’ known as the integrated straylight parameter. k’ provides an alternative to the commonly used straylight parameter, k. Results: Preliminary results in a small sample of normals showed k’ to be affected by age, diurnally, and by the menstrual cycle. Little variation in k’ was found between the ages of 16 and 42 years, with an increase found after the age of 60. A diurnal variation was found, with increased values of k’ on waking, which may be related to variation in cornea1 thickness. A variation in k’ with the menstrual cycle was noted. All values, i.e. n, k, k’ were found to be affected by keratoconus, cataract and cornea1 dystrophy. Conclusion: k’ is an important parameter in the quantification of scattered light. The results obtained give an insight into the patient’s symptoms of glare, essential in the timing of conducting penetrating keratoplasty. Acknowledgement: M. L. Hennelly was supported by a College of Optometry Studentship.
Increased incidence of Acanthamoeba keratitis associated with contact lens wear: the need to prevent this waterborne infection D. Seal, J. Hay, 0. M. Kirkness and West of Scotland Keratitis Study Group Tennent Institute of Ophthalmology, Western Infirmary, Glasgow Gil 6NT, UK The incidence of Acanfhamoeba keratitis has been assessed in the 1995 West of Scotland Keratitis Study. All patients with microbial keratitis in the 3 million population were reported to us prospectively by optometrists, ophthalmologists and microbiologists. Contact lens (CL) wearing patients completed detailed questionnaires; 50 healthy CL wearers were visited at home as controls and similarly investigated. Additionally all 340 optician practises were polled for their annual turnover of CL types and disinfectant solutions. Acanthamoeba keratitis occurred with an incidence of l/l0000 CL wearers based on this large, reliable community study of 164 000 CL wearers. This is 2.5 times more frequent than the previous American estimate (i.e. 1 :250 000). The relationship to CL material type, ineffective cold chemicals solutions and hygiene compliance is complex, but is directly related to use of contaminated tap water as part of CL care, this vehicle being the source of the amoebae. These findings are of considerable concern. They suggest that many new cases of painful, distressing and potentially blinding infection will be seen in Asia as CL wear becomes more widely available. Local expertise for recognition of Acanrhamoeba keratitis will be required plus treatment with a combination of 0.02% chlorhexidine and 0.1% propamidine. Tap water must be avoided in CL care, and rigorous attention paid to CL hygiene.
Anion binding in bovine cornea1 stroma Douglas H. Kerswell and Stuart A. Hodson Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF, UK Purpose: The cornea1 stroma strives to take up water because of the osmotic gradient created by fixed negative charges within the stroma. This fixed negative charge is known to be partly due to glycosaminoglycans and thought to be partly due to bound Cl- ions in the stroma. This study investigates the presence of anion binding within bovine stroma. Methods: Bovine corneas were isolated, de-epithelialized and deendothelialized. The stromal uptake of NaCl, NaAcetate, NaThiocyanate and NaHCO, solutions at various concentrations was observed using a digital balance. The dry weight of each cornea was noted. Stromal hydrations were calculated and analysed. Results: As the bathing solution concentration increased, for all solutions