Optometry and Vision Science

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This is the collection for the University of Waterloo's School of Optometry and Vision Science.

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The Effects of 1-(5-Iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7) on the Lens During Avian Accommodation In Situ
(University of Waterloo, 2009-12-17T18:34:02Z) Luck, Sara
A previous study in chickens revealed that myosin light chain kinase (MLCK), f actin, and myosin are found on the crystalline lens. Their polygonal arrangement at the posterior surface resembles a muscle tissue, which suggests that these proteins may have a contractile role in accommodation. The ciliary muscle in chickens is skeletal in nature and, therefore, chickens were used to test the hypothesis that contractile microfilaments play a role in accommodation. Ciliary nerve-induced accommodation was measured in the presence of an MLCK inhibitor 1-(5-Iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7). Eyes of 6-day old white Leghorn chickens (gallus gallus domesticus) were enucleated in Tyrode’s saline solution while keeping the ciliary nerve intact. One eye was treated with ML-7 and the other eye was treated with vehicle only. Three concentrations of ML-7 were used: 1 µM, 10 µM, and 100 µM. Two experiments were carried out, one including a (3×10 min) wash and one without. Focal lengths of the vehicle- and ML-7-treated eyes were measured before, during and after accommodation. Immunoblots were used to detect the amount of phosphorylated myosin with and without the inhibitor. Focal lengths for accommodation were shorter than those at rest (p<0.001). In the wash experiment, vehicle-treated eyes had higher accommodative amplitudes compared to ML-7-treated eyes for all three dosage groups. In the no-wash experiment, only the 1 µM group demonstrated the same trend as the wash experiment. For the 10 µM and 100 µM groups, ML-7-treated eyes had higher accommodative amplitudes compared to vehicle-treated eyes. Immunoblots revealed varying amounts of inhibition within pairs of eyes as well as between birds for both experiments. Results from this experiment indicate that ML-7 was not effective at determining whether contractile microfilaments found on the lens contribute to accommodation.
Effects of ML-7 on the Actomyosin Networks of the Avian Crystalline Lens
(University of Waterloo, 2022-04-29) Suko, Adeline
Assemblies of contractile proteins such as actin, myosin and myosin light chain kinase (MLCK) are found on the posterior surface of the lens fibre cells. The mechanical properties of chicken lenses, as well as their focal lengths, were found to be affected by the disruption of the network using inhibitors such as 1-(5-Iodonaphthalene-1sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7). The purpose of this study is to determine if ML-7, a MLCK inhibitor influences actomyosin organization in the chicken lens, which may have lead to the reported changes in stiffness and focal lengths. The Nearest Neighbour Distance (NND) values will be used to test the following hypotheses: ML-7-treated lenses have further NNDs compared to their vehicle counterparts, and that the NNDs of the 100μM-treated lenses would be lower than the lenses treated with lower concentrations (1μM and 10μM) of ML-7. Eyes of 7-day old white leghorn chickens (gallus gallus domesticus) were obtained. The anterior segment of one eye is treated with 1μM, 10μM, or 100μM of ML-7, and the other, with vehicle. The lenses were stained for actin and myosin. The NNDs for actin-actin, actin-myosin, myosin-actin and myosin-myosin were determined from confocal images of the networks to quantify the network distribution. Myosin-myosin NNDs of 10μM-treated lenses showed significantly lower values compared to 100μM-treated lenses. However, it is uncertain whether the significant change observed was indeed due to ML-7 activity or due to variation between birds. Additionally, only myosin-actin NNDs showed a significant reduction in treated lenses. These results suggest that actomyosin interactions affected by ML-7 may have been too subtle to detect, or compensation by other kinases occurred. Thus, this study was unable to determine if the stiffness and focal length changes in ML-7-treated lenses observed in previous studies were related to changes that ML-7 imparts on the actomyosin networks.
Is blur sensitivity altered in children with progressive myopia?
(Elsevier, 2019-01) Labhishetty, Vivek; Chakraborty, Arijit; Bobier, William
School aged children with progressive myopia show large accommodative lags to blur only cue which is suggestive of a large depth of focus (DOF). While DOF measures are lacking in this age group, their blur detection and discrimination capacities appear to be similar to their non-myopic peers. Accordingly, the current study quantified DOF and blur detection ability in progressive myopic children showing large accommodative lags compared to their non-myopic peers and adults. Blur sensitivity measures were taken from 12 children (8–13 years, 6 myopes and 6 emmetropes) and 6 adults (20–35 years). DOF was quantified using step changes in the lens induced defocus while the subjects viewed a high contrast target through a Badal lens at either 2 or 4D demand. Blur detection thresholds (BDT) were tested using a similar high contrast target in a 2-alternate forcedchoice paradigm (2AFC) at both the demands. In addition to the large accommodative lags, micro fluctuations and DOF were significantly larger in myopic children compared to the other groups. However, BDTs were similar across the three groups. When limited to blur cues, the findings of a large DOF coupled with large response lags suggests that myopes are less sensitive to retinal defocus. However, in agreement to a previous study, refractive error had no influence on their BDTs suggesting that the reduced sensitivity to the defocus in a myopic eye appears to be compensated by some form of an adjustment in the higher visual processes to preserve the subjective percept even with a poor retinal image quality.
Reading Additions in Children and Young Adults with Low Vision – Effects on Reading Performance
(University of Waterloo, 2011-02-24T21:26:53Z) Alabdulkader, Balsam
Reading is one of the most important activities in most people’s life. For children, reading is a window to knowledge, good educational achievement and better job opportunities in the future. Thus reading fluency is a very important factor in the child’s education. Children and young adults with low vision usually use a close working distance to gain relative distance magnification. Unlike adults, they have active accommodation. Many studies, however, have shown that children and young adults with low vision have reduced accommodation response compared to the norms of their age. Reading additions (high plus lenses) can correct for this reduction in accommodation and may be an optimum method of prescribing magnification in younger adults with low vision. There have been no studies to verify the best method of prescribing reading additions in young adults with low vision and few studies of their effect on reading performance. This is the first study to compare different methods to determine reading additions and their effect on reading performance in young adults with low vision. The aims of the present study are 1) to investigate if three different methods to determine reading additions would lead to significantly different dioptric powers 2) to determine which method (if any) would lead to better reading performance. Reading performance was assessed by measuring the maximum reading speed, critical print size (CPS), print size threshold and the area under the reading speed curve. This was an experimental study involving thirty participants with low vision aged between 8 to 35 years. Participants were recruited from the Low Vision Clinic at the School of Optometry, University of Waterloo, Canadian National Institute for the Blind (CNIB) and the Vision Institute of Canada. All participants underwent a routine clinical examination including distance visual acuity, near visual acuity, Pelli-Robson contrast sensitivity, unilateral cover test, static retinoscopy, subjective refraction and measurement of the habitual reading distance. A questionnaire was used to determine their usage of any low vision aids, their perceived difficulty with reading and time spent reading. Reading additions were determined by 1) an objective method using Nott dynamic retinoscopy 2) an age-based formula 3) a subjective method based on the participant’s response to lenses. Reading tasks and dynamic retinoscopy were conducted at a fixed working distance of 12.5cm. Reading performance was assessed using MNREAD-style reading charts with each of the reading additions and without a reading addition, in a random order. Sentences were arranged in way that no sentence was repeated by the same participant. Participants were timed with a stop watch in order to calculate the reading speed in correct words per minute (CWPM). Reading speeds were plotted against print size to calculate the maximum reading speed, the critical print size, MNREAD threshold and the area under the reading speed curve. The participant’s mean age was 16 (± 6) years. There were equal number of males and females. The mean distance visual acuity of the tested eye ranged from 0.357 to 1.184 logMAR with a mean of 0.797 ± 0.220 logMAR. The near visual acuity ranged between 0.301 to 1.301 logMAR with a mean of 0.80 ± 0.26 logMAR. There were six participants who already had a reading addition. Maximum reading speed ranged between 52 to 257 wpm (165 ± 61 wpm). Critical print size ranged between 0.325 to 1.403 logMAR (0.965 ± 0.279 logMAR). Repeated measures ANOVA on the whole group showed that there was a significant difference between the reading additions (p=0.001). The retinoscopy reading addition power was significantly lower than the age add (p=0.002) and the subjective add (p=0.038). Repeated measures ANOVA did not show any improvement of any of the reading measures with the reading additions compared to without the reading addition. A re-analysis was undertaken excluding participants who had normal accommodation at 12.5cm. The results of repeated measures ANOVA showed that there was no significant difference in the dioptric powers obtained by the three methods, although, all reading addition power were significantly greater than zero (t-test <0.0005). There was a significant difference in the area under the reading speed curve (p=0.035), which was greater with the subjective addition than with no reading addition (p=0.048). The MNREAD threshold significantly improved with the age addition compared to no addition (p=0.012). There was a large variability between the participants in their response to a reading addition. Analysis of individual data showed that some participants showed a clear improvement in reading performance with a reading addition. Other participants did not demonstrate any obvious improvement in reading performance with reading additions. Of those participants who showed an improvement, all but one participant had abnormal accommodation. However, not all participants who did not show an improvement had normal accommodation. Univariate analysis and forward step-wise linear regression analysis were used to investigate if any improvement in reading performance and the habitual reading performance without a reading addition could be predicted by factors that were measured in the study. These factors included distance visual acuity, near visual acuity, contrast sensitivity, lag of accommodation, age, time spent on reading each day, perceived difficulty of reading regular print and whether or not the participant received training for the usage of his/her low vision aids. Improvement in reading performance could not be predicted by any of these factors. Habitual reading performance without a reading addition was correlated with some factors. Univariate analysis showed that critical print size was associated with MNREAD threshold (r=0.904. p<0.0005), distance visual acuity (r=0.681, p<0.0005) and contrast sensitivity (r=-0.428, p=0.018) and MNREAD threshold without an addition was associated with the contrast sensitivity (r=-0.431, p=0.017,) and distance visual acuity (r=0.728, p<0.0005). Difficulty of reading correlated with near visual acuity (Spearman correlation coefficient=0.620, p=0.0009), MNREAD threshold (Spearman correlation coefficient=0.450, p=0.02) and maximum reading speed (Spearman correlation coefficient=-0.472, p=0.014). Time spent on reading each day correlated with the area under the reading speed curve (Spearman correlation coefficient=0.659, p=0.0024). The multiple regression analysis showed that MNREAD threshold was best predicted by distance visual acuity (R=0.728, p <0.0005), critical print size could be predicted by distance visual acuity (R=0.681, p <0.0005) and age (R=0.748, p=0.022) and the power of the subjective addition could be predicted by age (R=0.583, p=0.001) and near visual acuity (R=0.680, p=0.028). There was evidence that a reading addition improved reading performance as measured by the area under the curve and MNREAD (reading acuity) thresholds, but this was not predicted by any visual factor, except that all those who gained improvement had poor accommodation. Therefore, it is recommended that an eye care practitioner should demonstrate a reading addition in a low vision assessment of children and young adults, particularly with patients who have reduced accommodation.

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Browsing Optometry and Vision Science by Subject "accommodation"