Mahesh Raj Joshi

University of Plymouth | UoP · School of Health Professions

In clinical testing of visual acuity, it is often assumed that performance reflects sensory abilities and observers do not exhibit strong biases for or against specific letters, but this assumption has not been extensively tested. We re-analyzed single-letter identification data as a function of letter size, spanning the resolution threshold, for 1...

Introduction: Contact lens (CL) practice is an ever-changing field with clinical knowledge, techniques and equipment continuously evolving. These new developments are backed with clinical trials and research to ensure that practitioners feel confident that there is an evidence base to support these advances. Evidence-based practice is now a crucia...

SIGNIFICANCE This article reviews educational standard, clinical practice, research advances, and challenges associated with optometry in Nepal and provides critical considerations for contemporary and new optometry programs in countries with similar socioeconomic status and health care systems. Optometry education started in Nepal in 1998 with the...

Background: Keratoconus is associated with thinning and anterior protrusion of the cornea resulting in the symptoms of blurry and distorted vision. The commonly used clinical vision tests such as visual acuity and contrast sensitivity may not reflect the symptoms experienced in keratoconus and there are no quantitative tools to measure visual dist...

Previous studies have demonstrated that similarity and bias are major causes of errors in the identification of Sloan letters in visual acuity testing. However, these two factors and their relative contribution have not been investigated extensively at central and paracentral visual field locations. Using the method of constant stimuli, visual acui...

Sloan letters are one of the most commonly used optotypes in clinical practice. Sloan letters have different relative legibility which could be due to three factors: perceivability, response bias, and similarity. Similarities between Sloan letters are known to be the major source of errors in threshold determination. However, little is known about...

In clinical testing of visual acuity and contrast sensitivity, it is often assumed that data reflect sensory performance and observers do not exhibit strong biases for or against specific letters, but this assumption has not been extensively tested. We measured letter identification performance against letter size, spanning the resolution threshold...

Global motion and global form are proposed to be processed through functionally differentiated independent channels along dorsal (motion) and ventral (form) pathways. However, more recent studies show significant interactions between these pathways by inducing the perception of motion (implied motion) from presenting the independent frames of stati...

Aim To determine if a gradual adaptation period is necessary for neophytes when fitted with modern hydrogel or silicone hydrogel reusable disposable contact lenses. Method Across four sites, 74 neophytes (18–28 years) were randomly assigned to a reusable lens cleaned nightly with Opti-Free® Puremoist® multi-purpose contact lens solution: Proclear®...

Optometry education in Nepal began in 1998 in collaboration with the University of Auckland, New Zealand, with the primary objective of addressing the unmet needs of eye health and vision care. Over the last two decades, the development of optometry education has seen significant progress, including a shift from a three-year to a four-year curricul...

Purpose To determine the causes of visual impairment and the use of low vision devices in patients attending the low vision clinic in Trinidad and Tobago. Methods A retrospective study of the 222 patients attending the low vision clinic at the University of the West Indies, St Augustine Campus was conducted. The presenting visual acuity, causes of...

Purpose Letter resolution depends on three factors: perceivability, response bias, and similarity. The aim of the present study was to investigate the effect of response bias (the sensory-independent factor) on resolution thresholds of Sloan letters in central and paracentral vision. Methods Nine subjects with normal ocular health were recruited f...

Purpose: Global motion and global form perception have been found to be abnormal in the presence of amblyopia. How such deficits manifest in visual function reliant on the interactions between these two visual processing mechanisms has not been adequately explored. In the current study, we use dynamic Glass patterns (dGlass) to measure implied mot...

Purpose To establish the optimum grading increment which ensured parity between practitioners while maximising clinical precision. Methods Second year optometry students (n = 127, 19.5 ± 1.4 years, 55 % female) and qualified eye care practitioners (n = 61, 40.2 ± 14.8 years, 52 % female) had 30 s to grade each of bulbar, limbal and palpebral hyper...

Glass patterns with varying elements and line segments have been used to investigate global form processing. However, if these different stimuli target similar local or global form processing mechanism is not known. A total of 5 visually normal participants discriminated orientation of Glass patterns composed of different component element (2 eleme...

Purpose: To quantitatively measure the perceptual distortion experienced by individuals with keratoconus and correlate the magnitude of distortion with corneal structural measurements. Methods: A total of 25 adults (mean age = 29.84 ± 7.46 years) with keratoconus underwent measurements of visual and refractive status, corneal topography, and centr...

Global motion and global form perception is known to be abnormal in amblyopia. However, how such deficits manifest in the visual function thought to be reliant on the interactions between the two processing mechanisms, such as the perception of implied motion, is yet to be explored. A total of 13 amblyopes (8 strabismic and 5 anisometropic) and 6 n...

Purpose: Directly comparing the motion and form processing in neurologic disorders has remained difficult due to the limitations in the experimental stimulus. In the current study, motion and form processing in amblyopia was characterized using random dot stimuli in different noise levels to parse out the effect of local and global processing on m...

Motion and form processing along the functionally differentiated dorsal and ventral stream is reported to be abnormal in amblyopia; however limitations in previous stimuli have made analogous comparison of the outputs from these two streams difficult. In the current study, we characterise both functions in amblyopia using equivalent stimuli for fin...

Abnormal motion and form processing along the dorsal or ventral pathway has been reported in amblyopia. In the current study, we attempted to characterise visual processings in both pathways in amblyopia concurrently using equivalent stimuli in the presence of noise. Six anisometropes, six strabismics, and 12 visually normal observers monocularly d...

Background: Usher syndrome is a rare autosomal recessive disorder characterized by congenital sensory neural deafness and progressive visual loss secondary to retinitis pigmentosa. There are three different types of Usher syndrome. Retinitis pigmentosa is the main ophthalmic manifestation shared by all three. Differences in auditory and vestibular...

The development of sensitivity to radial optic flow discrimination was investigated by measuring motion coherence thresholds (MCTs) in school-aged children at two speeds. A total of 119 child observers aged 6-16 years and 24 young adult observers (23.66 +/-2.74 years) participated. In a 2AFC task observers identified the direction of motion of a fi...

Background: To evaluate peripapillary retinal nerve fiber layer (RNFL) thickness in glaucomatous Nepalese eyes using spectral domain optical coherence tomography (SD-OCT) and study its relationship with visual field sensitivity. Methods: A total of 120 eyes comprising primary open angle glaucoma (POAG), glaucoma suspects (GS), normal tension gla...

The visual system is functionally differentiated into dorsal (motion) and ventral (form) pathways, owing to the limitations in previously employed stimuli analogous comparison of the outputs from these two streams has proven difficult. In the current study, we adapted the equivalent noise paradigm to (1) disentangle the effect of local and global l...

The visual system is functionally differentiated into dorsal (motion) and ventral (form) pathways, owing to the limitations in previously employed stimuli analogous comparison of the outputs from these two streams has proven difficult. In the current study, we adapted the equivalent noise paradigm to (1) disentangle the effect of local and global l...

Current study evaluated the sensitivity to global motion and form perception which are presumably processed by two distinct visual pathways – dorsal and ventral respectively [Ungerleider and Mishikin, 1982, in: Analysis of Visual Behavior, Cambridge, MIT press] – in varying noise levels. We used Glass pattern [Glass, 1969, Nature, 223, 578-579] and...

The development of sensitivity to optic flow patterns was investigated by measuring motion coherence thresholds (MCTs) in school-aged children in Kathmandu. 119 child observers aged 6-16 years and 24 adult observers (mean age, 23.66 years) participated with informed consent. The observers identified the direction of a translational (rightward vs le...

Introduction: Global motion processing is an essential part of visual perception involving higher cortical areas. The motion coherence threshold (MCT) is used to evaluate global motion processing. Previous studies have investigated the development of translational optic flow processing in children but no study has yet evaluated MCT for radial op...

Introduction: Children from the developing world are more prone to going blind from avoidable and preventable causes. In Nepal, children in private schools are reported to have a higher ocular morbidity than those in government schools, with myopia being the major cause of the morbidity. This study was designed to evaluate ocular morbidity in stud...

Color vision defect can be observed in various diseases of optic nerve and retina and also a significant number of people suffer from the inherited condition of red and green color defect. A cross-sectional descriptive study was designed with purposive sampling of students from various schools of Kathmandu Valley. All children were subjected to col...

This study was carried out with the objective of finding refractive status of patients undergoing phacoemulsification surgery for cataract extraction. Success of cataract surgery can be quantified with the improvement in visual acuity with least amount of refractive error. Prospective study of 44 patients was done pre operatively and with subsequen...

In Nepal, children with low vision attend specialized schools for students who are totally blind and are treated as if they were totally blind. This study identified children with low vision and provided low vision devices to them. Of the 22% of the students in the school who had low vision, 78.5% benefited from the devices. Proper devices and coun...

A prospective cross sectional study of students of two private schools was done and students were screened in detail. A total of 1816 students aged 5 to 16 years were evaluated, out of which 52.8% were males and 47.2 % were females. Among the total, 65.8% had no ocular abnormalities and 34.2% had some form of ocular disorders. Refractive error was...