- Email: [email protected]
Binocular summation in the peripheral visual field
Abstracts There are various models to describe coupling between transmembrane Na- ilux and transendothelial net HCO, flux in the cornea, including a direct coupling via a Na+/HCOjm cotransporter or an indirect coupling utilizing a Na+/K+/2CI- cotransporter further coupled to a Cl-/HCO, exchanger. In this study we investigate the presence of Na+/K+/2CIcotransporter activity by using cornea1 endothelial cell plasma membrane vesicles. By controlling the external and internal compartments of the vesicles we were able to monitor Na+ movement across the membranes. If the Na+/K+/2Cl- cotransporter is present in the cornea1 endothelial cell membrane vesicles then the presence of K- should lead to a significant increase in uptake of **Na-. The rate of accumulation of z2Na+ in the presence of Kf was 25.7 F2.8 nmoles Na+ mgg protein 15 s-’ which was not significantly different from that in the absence of K+ (23.8 + 2.0 nmoles Na+ mg-’ protein 15 s-i) indicating that Nat uptake into the vesicles was not dependent on K+. The present work provides no evidence for Na+/K+/2CI- cotransport in cornea1 endothelial cell plasma membrane vesicles. The nature of the coupiing mechanism between HCO; and Na+ is still unresolved.
Binocular summation in the peripheral visual field Angela Whitaker and Shahina Pardhan Department of Optometry, University of Bradford, Bradford BD7 lDP, UK Purpose: To investigate binocular summation for a light detection task in the central and peripheral retina along 4 meridians. Methods: 10 young subjects aged 22-30 years (mean 26 years) with healthy eyes and normal visual fields participated in the study. A customdesigned program on a Humphrey Visual Field Analyser measured thresholds at the fovea and at 5”, lo”, 15”, 25”, 40” and 55” along the horizcntal meridian, and at 5”, lo”, 15”, 25”, 40” along the vertical, 45” oblique and 135” oblique meridians. Right and left monocular fields and binocular fields were measured on each subject using white spot stimuli (Goldmann sizes I and III). Binocular summation ratios were calculated for each eccentricity by dividing binocular sensitivity be the better monocular sensitivity. Results and conclusion: As expected, binocular and monocular sensitivities decreased with increasing eccentricity. The mean binocular summation ratio at the fovea was 1.38 for size I stimulus and 1.42 for size III. Binocular summation was demonstrated in the peripheral retina along all meridians and is of similar magnitude to fovea1 binocular summation. ANOVA showed that binocular summation was significantly higher in the vertical meridian than horizontal meridian for both size I and III stimuli. There was no significant variation in binocular summation ratios with eccentricity along any of the 4 meridians examined.
CAMP stimulates cornea1 endothelial HCO; transport K. Ogbuehi, C. G. Wigham and S. A. Hodson Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF, UK A previous study has demonstrated that cornea1 endothelial HCO, transport is stimulated by the non-specific phosphodiesterase (PDE) inhibitor IBMX. The objective of this study was to use more specific inhibitors of PDE isoenzymes to resolve which cyclic nucleotide is responsible for the observed effect of IBMX. Robpram. an inhibitor of CAMP hydrolysing PDE, and Zaprinast, an inhibitor of cGMP hydrolysing PDE, were added to de-epithelialized corneas mounted in vitro in modified Ussing-type chambers. Transendothelial potential difference (Pd,), resistance (R,) and short circuit current (SCC) were measured. To determine if Rolipram and Zaprinast increased cyclic nucleotide concentrations the intracellar concentrations of CAMP and cGMP were also determined. Rohpram (0.1 mM) significantly increased SCC in a transient manner. The maximum stimulated value for SCC was 16 I 3% above control (mean * SEM, n = 4). Rolipram also increased [CAMP], from 782 f 29 to 2167 f 111 pM rng-’ protein (mean i SEM, n = 36). Zaprinast
173
(0.5 mM) reversibly reduced SCC by 9 + 3% (mean & SEM, n = 3) and did not change [cGMP], which measured 370 f 15 pM mg-’ protein (mean f SEM, n = 36). Neither drug affected R,. These results demonstrate that PDE induced elevation of [CAMP], can increase cornea1 endothelial HCO; transport and that cGMP is apparently unchanged and without effect.
Symmetry detection in amblyopia B. T. Barrett’ and A. M. Herbert2 ‘Department of Optometry, University of Bradford, Bradford BD7 lDP, UK; 2Ecole d’optometrie, Universite de Montreal, Montreal, Canada H3C 3J7 Purpose: It has been suggested that the term tarachopia, meaning ‘distorted sight’, provides an accurate description of the visual deficit in amblyopia. This follows psychophysical findings of spatial inaccuracy in amblyopia, as well as subjective reports of perceptual distortions by amblyopic observers. Mirror symmetry is a salient feature in normal human vision and its detection is critically dependent upon the spatial relations between the elements of the pattern. This study investigates whether the perceptual distortions in amblyopia extend to mirror symmetry detection. Methods: Three strabismic and three non-strabismic amblyopes participated in the experiment (acuity range 619 to 6190). Symmetric and random dot patterns were briefly presented (< 250 msecs) at three retinal locations (centred at fixation, and 4” to the left and right of fixation). The patterns were generated and displayed on a Macintosh computer. After each stimulus presentation the subject was required to press one of two keys to indicate whether the pattern was symmetrical or random. The d’ statistic was computed for three symmetry orientations (H, V, and 45”) for each of the three retinal locations. Results: Amblyopic-eye performance was equivalent to fellow-eye performance in 5 of the 6 amblyopes tested. In the remaining amblyope symmetry detection in the amblyopic eye. This is likely to have resulted from reduced visibility of the dot pattern since the acuity in this eye was 6/90. Conclusions: The ability to detect mirror symmetry in briefly presented dot patterns is not affected by amblyopia.
A comparative study of the efficacy and topical cornea1 anaesthetics J. G. Lawrenson, D. F. Edgar and F. K. Department of Optometry and Visual University, Goswell Road, London EClV
tolerability
of
Rupra Science, City 7DD, UK
There are several topical anaesthetics available to the optometrist as a preservative-free unit dose formulation. There is little comparative data as to the efficacy and tolerability of these drugs. The aim of this study was to compare the depth and duration of cornea1 anaesthesia following instillation of one drop of 0.4% benoxinate, 0.5 % amethoCaine and 0.5% proxymetacaine. The tolerability of each anaesthetic was assessed using a linear lo-point arbitrary comfort scale. Fourteen male subjects participated in the study (mean age 26.6 + 5.0 years). Cornea1 sensitivity was measured using a slit-lamp mounted CochetBonnet aesthesiometer prior to installation, and at 1, 3, 5, 10, 15, 20, and 30 min after, and continued if necessary until cornea1 sensitivity had returned to pre-instillation levels. For each anaesthetic complete anaesthesia occurred within 1 min of instillation and a return to baseline sensitivity levels occurred by 30min. No significant difference in anaesthesia was found between drugs at each time point. In contrast tolerability profiles indicated that proxymetacaine was significantly better tolerated than either amethocaine (P < 0.01) or benoxinate (P < 0.001). This together with an excellent safety record makes proxymetacaine an ideal choice for optometric procedures requiring short-acting cornea1 anaesthesia.
Binocular summation in the peripheral visual field Angela Whitaker and Shahina Pardhan Department of Optometry, University of Bradford, Bradford BD7 lDP, UK Purpose: To investigate binocular summation for a light detection task in the central and peripheral retina along 4 meridians. Methods: 10 young subjects aged 22-30 years (mean 26 years) with healthy eyes and normal visual fields participated in the study. A customdesigned program on a Humphrey Visual Field Analyser measured thresholds at the fovea and at 5”, lo”, 15”, 25”, 40” and 55” along the horizcntal meridian, and at 5”, lo”, 15”, 25”, 40” along the vertical, 45” oblique and 135” oblique meridians. Right and left monocular fields and binocular fields were measured on each subject using white spot stimuli (Goldmann sizes I and III). Binocular summation ratios were calculated for each eccentricity by dividing binocular sensitivity be the better monocular sensitivity. Results and conclusion: As expected, binocular and monocular sensitivities decreased with increasing eccentricity. The mean binocular summation ratio at the fovea was 1.38 for size I stimulus and 1.42 for size III. Binocular summation was demonstrated in the peripheral retina along all meridians and is of similar magnitude to fovea1 binocular summation. ANOVA showed that binocular summation was significantly higher in the vertical meridian than horizontal meridian for both size I and III stimuli. There was no significant variation in binocular summation ratios with eccentricity along any of the 4 meridians examined.
CAMP stimulates cornea1 endothelial HCO; transport K. Ogbuehi, C. G. Wigham and S. A. Hodson Department of Optometry and Vision Sciences, University of Wales, Cardiff, PO Box 905, Cardiff CFl 3XF, UK A previous study has demonstrated that cornea1 endothelial HCO, transport is stimulated by the non-specific phosphodiesterase (PDE) inhibitor IBMX. The objective of this study was to use more specific inhibitors of PDE isoenzymes to resolve which cyclic nucleotide is responsible for the observed effect of IBMX. Robpram. an inhibitor of CAMP hydrolysing PDE, and Zaprinast, an inhibitor of cGMP hydrolysing PDE, were added to de-epithelialized corneas mounted in vitro in modified Ussing-type chambers. Transendothelial potential difference (Pd,), resistance (R,) and short circuit current (SCC) were measured. To determine if Rolipram and Zaprinast increased cyclic nucleotide concentrations the intracellar concentrations of CAMP and cGMP were also determined. Rohpram (0.1 mM) significantly increased SCC in a transient manner. The maximum stimulated value for SCC was 16 I 3% above control (mean * SEM, n = 4). Rolipram also increased [CAMP], from 782 f 29 to 2167 f 111 pM rng-’ protein (mean i SEM, n = 36). Zaprinast
173
(0.5 mM) reversibly reduced SCC by 9 + 3% (mean & SEM, n = 3) and did not change [cGMP], which measured 370 f 15 pM mg-’ protein (mean f SEM, n = 36). Neither drug affected R,. These results demonstrate that PDE induced elevation of [CAMP], can increase cornea1 endothelial HCO; transport and that cGMP is apparently unchanged and without effect.
Symmetry detection in amblyopia B. T. Barrett’ and A. M. Herbert2 ‘Department of Optometry, University of Bradford, Bradford BD7 lDP, UK; 2Ecole d’optometrie, Universite de Montreal, Montreal, Canada H3C 3J7 Purpose: It has been suggested that the term tarachopia, meaning ‘distorted sight’, provides an accurate description of the visual deficit in amblyopia. This follows psychophysical findings of spatial inaccuracy in amblyopia, as well as subjective reports of perceptual distortions by amblyopic observers. Mirror symmetry is a salient feature in normal human vision and its detection is critically dependent upon the spatial relations between the elements of the pattern. This study investigates whether the perceptual distortions in amblyopia extend to mirror symmetry detection. Methods: Three strabismic and three non-strabismic amblyopes participated in the experiment (acuity range 619 to 6190). Symmetric and random dot patterns were briefly presented (< 250 msecs) at three retinal locations (centred at fixation, and 4” to the left and right of fixation). The patterns were generated and displayed on a Macintosh computer. After each stimulus presentation the subject was required to press one of two keys to indicate whether the pattern was symmetrical or random. The d’ statistic was computed for three symmetry orientations (H, V, and 45”) for each of the three retinal locations. Results: Amblyopic-eye performance was equivalent to fellow-eye performance in 5 of the 6 amblyopes tested. In the remaining amblyope symmetry detection in the amblyopic eye. This is likely to have resulted from reduced visibility of the dot pattern since the acuity in this eye was 6/90. Conclusions: The ability to detect mirror symmetry in briefly presented dot patterns is not affected by amblyopia.
A comparative study of the efficacy and topical cornea1 anaesthetics J. G. Lawrenson, D. F. Edgar and F. K. Department of Optometry and Visual University, Goswell Road, London EClV
tolerability
of
Rupra Science, City 7DD, UK
There are several topical anaesthetics available to the optometrist as a preservative-free unit dose formulation. There is little comparative data as to the efficacy and tolerability of these drugs. The aim of this study was to compare the depth and duration of cornea1 anaesthesia following instillation of one drop of 0.4% benoxinate, 0.5 % amethoCaine and 0.5% proxymetacaine. The tolerability of each anaesthetic was assessed using a linear lo-point arbitrary comfort scale. Fourteen male subjects participated in the study (mean age 26.6 + 5.0 years). Cornea1 sensitivity was measured using a slit-lamp mounted CochetBonnet aesthesiometer prior to installation, and at 1, 3, 5, 10, 15, 20, and 30 min after, and continued if necessary until cornea1 sensitivity had returned to pre-instillation levels. For each anaesthetic complete anaesthesia occurred within 1 min of instillation and a return to baseline sensitivity levels occurred by 30min. No significant difference in anaesthesia was found between drugs at each time point. In contrast tolerability profiles indicated that proxymetacaine was significantly better tolerated than either amethocaine (P < 0.01) or benoxinate (P < 0.001). This together with an excellent safety record makes proxymetacaine an ideal choice for optometric procedures requiring short-acting cornea1 anaesthesia.