Optometry and Vision Science

Permanent URI for this collectionhttps://uwspace.uwaterloo.ca/handle/10012/9945

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

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

Waterloo faculty, students, and staff can contact us or visit the UWSpace guide to learn more about depositing their research.

Browse

Now showing 1 - 5 of 5

Can kynurenic acid cause myelin loss in chicken optic nerves?
(University of Waterloo, 2017-09-27) Gurdita, Akshay; Choh, Vivian
Kynurenic acid (KYNA) is one of many kynurenine intermediate products in the tryptophan metabolism pathway and has been shown to have neuro-activity. Previous work revealed that prolonged infusion of a high dose of KYNA could effectively reduce the myelin content in the rat spinal cord. We hypothesize that prolonged subdural infusion of kynurenic acid (KYNA) induces myelin loss in the optic nerves of chickens. Seven day old gallus gallus domesticus chickens were randomly selected for infusion of 50 mM KYNA or phosphate buffered saline (PBS). KYNA or PBS were loaded into an osmotic pump that was attached to a catheter. The catheter was inserted into the optic nerve and the pump was implanted under the skin in upper back region of the bird. A third group of birds received no treatment. Electron micrographs were collected and the percent of myelinated axons, g-ratios, the number of astrocytes, and the axon diameters were calculated by sampling from 4 quadrants of optic nerve sections. Enzyme-linked immunosorbent assays (ELISA) were performed on serum from the three groups in order to determine differences in the level of myelin proteins myelin basic protein (MBP) and proteolipid protein (PLP). Semi-quantitative analysis of western blots was performed for myelin proteins: MBP, PLP, and myelin associated glycoprotein (MAG) in addition to glial fibrillary acidic protein (GFAP). A 2x3 mixed model analysis of variance (ANOVA) was used to determine differences between the three treatment groups and eyes. Count data were analyzed using two one-way Kruskal-Wallis ANOVAs. Electron microscopy revealed that KYNA-infused nerves exhibited widespread loss of myelin sheaths and astrogliosis without inflammatory infiltration of the nerve. G-ratios for KYNA-infused chicks were greater than those for negative control birds (0.86 ± 0.04 for KYNA vs 0.78 ± 0.02 for NC; p = 0.0029) but were not significantly greater than compared to PBS-infused chicks (0.83 ± 0.06; p = 0.2605). ELISAs revealed no differences in the concentration of serum MBP or PLP across the three treatment groups indicating a non- destructive effect on myelin in the nerve (p = 0.8330 and p = 0.8759, respectively). Lastly, western blots revealed a qualitative reduction in the level of MBP and PLP, and GFAP in KYNA-infused birds compared to PBS-infused or negative control birds. Subdural infusion of 50 mM KYNA for 7 days induces myelin loss without inflammatory infiltration in the chicken optic nerve. KYNA may be useful for illuminating mechanisms in myelin production or oligodendrocyte function.
The Development of an Antibody-Drug Conjugate to Specifically Target and Soften the Crystalline Lens in vivo
(University of Waterloo, 2017-04-04) Won, Gah-Jone; Choh, Vivian
Helmholtz’s classical theory of accommodation states that, within the eye, contraction of the annular ciliary muscle releases the passive tension of zonules that hold the lens in a flattened state. As a result, the surface curvature of the lens steepens, and so too does dioptric power of the eye, allowing for nearby vision. It was also hypothesized that presbyopia, the age-related loss of accommodation, is due to the loss of ability for the lens to deform with age. Recently, the crystalline lens has been shown to possess a network of actomyosin filaments that are organized to help give the lens structural integrity. Given that cytoskeletal proteins are known to contribute to the integrity and biomechanical properties of cells, the question is raised of whether lenticular cells and the lens as a whole are affected by changes to these proteins and their distributions, and if so, whether a drug therapy can be designed to specifically target and soften the crystalline lens by inhibiting cytoskeletal protein interactions. This study was carried out in three stages: (1) Investigating the effects of various physiological inhibitors on the overall stiffness of the crystalline lens. (2) The development of a targeted drug therapy using one of the aforementioned inhibitors. (3) Testing the newly synthesized targeted drug therapy on an in vivo system, and assessing its effect on the accommodative system.
Effects of ML-7 on the Actomyosin Networks of the Avian Crystalline Lens
(University of Waterloo, 2022-04-29) Suko, Adeline; Choh, Vivian
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.
Effects of Temperature on the Proliferation of Human and Fish Lens Epithelial Cells
(University of Waterloo, 2019-08-29) Li, Ziqing; Choh, Vivian; Sivak, Jacob
Crystallins are proteins that confer refractive properties to the crystalline lens. All vertebrate lenses contain α- and β-crystallins, and often a third major crystallin. Crystallins can have additional non-refractive functions; α-crystallins act as heat shock proteins, protecting lenses from heat-induced denaturation, and γ-crystallins are thought to be cryoproteins, protecting lenses from extreme cold. The concentration of α-crystallins is higher in mammalian lenses than in teleost lenses, while the opposite is true for γ-crystallins, suggesting that mammalian lenses would be better protected in warmer conditions and teleost lenses better protected in colder temperatures. This study determined whether temperature affects the growth of lens epithelial cells (LECs) derived from human and fish lenses. Both human and rainbow trout fish LECs were cultured (n = 4 each) and grown for 1, 2, 4, 6, 8 and 12 days at the optimal (37°C and 18°C, respectively), higher than optimal (42°C and 25°C, respectively) and lower than optimal temperatures (32°C and 10°C, respectively). At optimal temperatures, both fish and human LECs grew optimally. Higher temperatures were more deleterious to the proliferation index than lower temperatures for both human and fish LECs. Mitotic cells were non-existent in fish LECs grown at high temperatures. The sizes of the cells did not greatly change with temperature with either species, but human cells at non-optimal temperature tended to clump over time. Human LECs at the optimal temperature maintained their random distribution. Fish LECs at optimal temperatures moved from a random distribution to a clumped distribution, but lower temperatures had the opposite effect; LECs moved from a clumped to a random distribution. Only the high temperature group of fish LECs maintain their random organisation.
Electrophysiological measures of optic nerve function
(University of Waterloo, 2021-08-26) Afari, Clement; McCulloch, Daphne; Choh, Vivian
The contribution of retinal ganglion cells (RGCs) to human electroretinograms (ERGs) is known, but that of chicken (Gallus gallus domesticus) is not clear. This project seeks to determine the effect of RGC dysfunction on full-field flash ERGs in chickens using established protocols known to test RGC function in humans and other mammals. Chicks were treated to produce unilateral retinal dysfunction by surgical optic nerve section (ONS group) or by intravitreal injection of tetrodotoxin (TTX group) to block ganglion cell function. Contralateral eyes received sham treatments, consisting of sham surgery or injections of vehicle, phosphate buffered saline (PBS), respectively. For both groups, bilateral, full-field ERGs were recorded in dark-adapted (DA) birds (ONS: n=6; TTX: n=5) or in light-adapted (LA) birds (ONS: n=10; TTX: n=5) prior to the imposed treatment (at one-day post-hatch) and on days 3-, 5-, 7-, 14-, and 21- post-treatment on the same birds. In addition, bilateral, full-field, long-flash (150 ms) ERGs were recorded from light-adapted birds (ONS: n=8; TTX: n=5) prior to treatment (at one day post-hatch) and again at 3-, 14- and 21-days post-treatment. Interpolation and curve fitting, including Naka Rushton fitting, were used to report parameters of the ERG stimulus-response series such as maximum amplitudes (Vmax) and sensitivity (k, stimulus producing half Vmax). Cell counts (retinal histology) were conducted of the RGC and inner nuclear layers from histological sections of a separate group of 6 birds sacrificed at 21 days post-ONS. For both groups, the measures of the DA ERG stimulus-response series (dark-adapted Vmax and k, the oscillatory potential amplitudes, and the interpolated a-wave parameters) did not differ between the treated and sham-treated eyes in either treatment group. In addition, for both treatment groups, the negative waveform of the scotopic threshold response (STR), which reflects RGC function in most mammals, was not apparent in the chick ERGs to dim flashes. No differences between the eyes were v detected for the positive STR/DA b-wave to 0.01 cd.s/m2 flashes (ONS: p=0.59; TTX: p=0.21). Similarly, the photopic negative response (PhNR) following the light-adapted b-wave was small and showed no effect of either treatment (ONS: p=0.92; TTX: p=0.11). However, the offset positivity, the d-wave amplitude, was smaller in the treated eyes in both the ONS and TTX groups (ONS: p=0.008; TTX: p=0.03), but d-wave implicit times did not differ. Cell counts confirmed that RGCs were selectively lost following ONS (p<0.0001). This study suggests that the STR and PhNR do not reflect RGC functions in chickens, as they do in most mammals. Anatomical differences between the chicken and human retinae might underlie differences in the generation of ERG waveforms associated with ganglion cells. In particular, chicken eyes, and avian eyes in general, lack an inner retinal blood supply and associated intra-retinal astroglia which may be necessary for the generation of STR and PhNR waveforms. Finally, this thesis showed that, unlike in humans, the chicken d-wave may reflect the function of cells in the optic nerve including RGCs and cells of the centrifugal vision system in the chicken.

Browse

Browsing Optometry and Vision Science by Author "Choh, Vivian"