A technique for accurate superimposition of computerized perimetry data onto the corresponding retinal locations seen on fundus photographs was developed. The technique was designed to take into account: 1) that the photographic field of... more
A technique for accurate superimposition of computerized perimetry data onto the corresponding retinal locations seen on fundus photographs was developed. The technique was designed to take into account: 1) that the photographic field of view of the fundus camera varies with ametropia-dependent camera focusing 2) possible distortion by the fundus camera, and 3) that corrective lenses employed during perimetry magnify or minify the visual field. The technique allowed an overlay of perimetry data of the central 60 degrees of the visual field onto fundus photographs with an accuracy of 0.5 degree. The correlation of localized retinal morphology to localized retinal function was therefore limited by the spatial resolution of the computerized perimetry, which was 2.5 degrees in the Dicon AP-2500 perimeter employed for this study. The theoretical assumptions of the technique were confirmed by comparing visual field records to fundus photographs from patients with morphologically well-defined non-functioning lesions in the retina.
ABSTRACT Amblyopia is a developmental ocular disease of childhood-onset which may lead to persistent sequelae into adulthood. Early detection and management of amblyopia usually result in an improved visual outcome. The purpose of this... more
ABSTRACT Amblyopia is a developmental ocular disease of childhood-onset which may lead to persistent sequelae into adulthood. Early detection and management of amblyopia usually result in an improved visual outcome. The purpose of this study was to determine the prevalence and pattern of amblyopia in a rural hospital in Ghana. Clinical records of patients seen (from January 2014 to December 2018) at Westphalian Medical Center, Oyoko, Ashanti Region, Ghana, were reviewed retrospectively. Unilateral amblyopia was defined as a two-line interocular difference or more in visual acuity. Bilateral amblyopia was defined as best-corrected visual acuity (BCVA) of Snellen 6/12 or worse in both eyes, with evidence of bilateral ametropia or obstruction of the visual pathway. Following a review of 12,602 patient records, 258 cases of amblyopia were identified. The mean (±SD) presenting age of amblyopic patients was 24.3 ± 16.1 years, with a male-to-female ratio of 1:1.1. The period prevalence of amblyopia was 2.04%. The period prevalence of unilateral and bilateral amblyopia was 1.38% and 0.66%, respectively. The most prevalent form of amblyopia was refractive with a cumulative prevalence of 1.42%. Strabismic and stimulus deprivation amblyopia accounted for 0.36% and 0.21% of all amblyopic cases, respectively. A major cause of amblyopia in this population was refractive error, hence the use of spectacle correction for its initial management. Repeated assessment after an appropriate period of refractive adaptation would elucidate the proportion of amblyopias needing additional treatment modalities. Vision screening for early detection of amblyopia in childhood with accessible and effective management of amblyopia (including refractive correction and occlusion treatment) is necessary to reduce the impact of amblyopia in Ghana.
To examine the prevalence of anisometropia of spherical refraction (AnisoSR), astigmatism (AnisoAST) and spherical equivalent (AnisoSE) and their associations with spherical refraction (SR), refractive astigmatism (AST), spherical... more
To examine the prevalence of anisometropia of spherical refraction (AnisoSR), astigmatism (AnisoAST) and spherical equivalent (AnisoSE) and their associations with spherical refraction (SR), refractive astigmatism (AST), spherical equivalent (SE) and interocular differences of ocular biometric parameters among elderly female twins. Refraction of 117 monozygotic (MZ) and 116 dizygotic (DZ) female twin subjects aged 66-79 years was assessed with an auto-refractor (Topcon AT) and controlled by subjective refraction. Corneal refraction, anterior chamber depth and axial length were measured with a Zeiss IOL Master. Participants with eyes operated for cataract or glaucoma were excluded, but the grade of nuclear opacity was not recorded. The associations between the absolute values of AnisoSR, AnisoAST and AnisoSE with SR, AST, SE, corneal refractive power (CR), corneal astigmatism (CAST), anterior chamber depth (ACD) and axial length (AL) and with their interocular differences were calcul...
A total of 268 elderly persons living in eight nursing homes in northern Finland (participation rate 100%) were examined by an ophthalmologist in 1980-1983 in order to describe visual acuity and the occurrence of refractive errors.... more
A total of 268 elderly persons living in eight nursing homes in northern Finland (participation rate 100%) were examined by an ophthalmologist in 1980-1983 in order to describe visual acuity and the occurrence of refractive errors. Uncorrected distant visual acuity in the better eye was less than 0.4 in 76% of the men and 68% of the women, being worse in older subjects than in younger ones. Uncorrected near visual acuity in the better eye was less than 0.1 in 24% of the men and 25% of the women. Hyperopia was found in 78% of the men and 77-78% of the women and myopia in 14-15% of the men and 15-16% of the women. Hyperopia decreased and myopia increased with age. Astigmatism was uncommon and its prevalence figure was not related to sex or age. Only 3% of men and 5% of women were emmetropic. We may conclude that uncorrected distant visual acuity of the population was low, and three out of every four men and two out of every three women were unable to manage their daily activities with...
Vernal Keratoconjunctivitis (VKC) is an allergic disease that typically affects young individuals, of which males are predominant. The disease involves the lids, conjunctiva, limbus and the cornea. The corneal changes range from punctate... more
Vernal Keratoconjunctivitis (VKC) is an allergic disease that typically affects young individuals, of which males are predominant. The disease involves the lids, conjunctiva, limbus and the cornea. The corneal changes range from punctate keratitis to shield ulcers. High incidences of keratoconus and abnormal corneal topographic patterns have been reported in these cases. The configuration of the corneal surface and the abnormal pattern of corneal surface can lead to vernal keratoconjunctivitis. Hence, an association between refractive errors and vernal keratoconjunctivitis was needed to be made.In our study we compared the refractive error with the stage of vernal keratoconjunctivitits (acute or chronic). Also we have tried to compare the type (limbal, bulbar or mixed) with the refractive error. Materials and methods: Fifty patients, ages ranging between 3 and 20 years, with Vernal Keratoconjunctivitis attending the ophthalmology outpatient department at Sri Siddhartha Medical College from December 2015 to December 2016 were included in the Study. The demographic data were noted, slit lamp evaluation and refractive error assessment were done for all patients. The data was compiled on a percentile basis of the two variables. Chi-square and Fisher's exact statistical analysis was used to study the association. Results: We found a male preponderance (78%) for the disease. Hypermetropia was the commonest (48% of patients) refractive error. Maximum patients manifested with signs of chronic Vernal Keratoconjunctivitis (76% patients). Bulbar type of Vernal Keratoconjunctivitis was commonest in our study group, (76% of patients). On evaluating the association of refractive error type with stage of Vernal Keratoconjunctivitis, the P value was not significant, thus indicating their independence. Also on evaluating the type of refractive error with the clinical variant of Vernal Keratoconjunctivitis, the p-value was not significant suggesting that they were independent. Conclusion: We found hypermetropia to be the commonest refractive error associated with VKC, followed by myopia and astigmatism. Perilimbal pigmentation suggestive of chronic Vernal Keratoconjunctivitis was the commonest stage of manifestation seen. Bulbar Vernal Keratoconjunctivitis was the commonest clinical type. There was no conclusive evidence to show an association between the refractive error and the stage and type of Vernal Keratoconjunctivitis
Refractive error is the most common cause of vision impairment among children, and schools with long period of engagement in vision screening were effective in detecting undiagnosed cases. The aim of this study was to assess the... more
Refractive error is the most common cause of vision impairment among children, and schools with long period of engagement in vision screening were effective in detecting undiagnosed cases. The aim of this study was to assess the prevalence of refractive error among female primary school children. A cross-sectional study was carried out from February to March 2013 using structured questionnaire and visual examination. Visual acuity of 324 students was assessed using the Snellen’s chart. Those with VA 6/12 or less with or without correction in one or both eyes were examined by pinhole test, and an improvement of the VA with pinhole was considered refractive error. The prevalence of RE was 16.4%, and a significant relationship was found between having RE in one side and having a family history of wearing glasses, higher class grades, poor school performance, watching television at a distance less than 3 meters, using internet / TV daily for more than 3 hours, and indulgence in computer...
Refractive errors are a major cause of visual impairment in the population. To find the pattern of refractive errors among patients evaluated in a tertiary care hospital in the western region of Nepal. The present hospital-based... more
Refractive errors are a major cause of visual impairment in the population. To find the pattern of refractive errors among patients evaluated in a tertiary care hospital in the western region of Nepal. The present hospital-based retrospective study was conducted in the Department of Ophthalmology of the Manipal Teaching Hospital, situated in Pokhara, Nepal. Patients who had refractive error of at least 0.5 D (dioptre) were included for the study. During the study period, 15,410 patients attended the outpatient department and 10.8% of the patients were identified as having refractive error. The age of the patients in the present study ranged between 5 - 90 years. Myopia was the commonest refractive error followed by hypermetropia. There was no difference in the frequency of the type of refractive errors when they were defined using right the eye, the left eye or both the eyes. Males predominated among myopics and females predominated among hypermetropics. The majority of spherical er...
The major types of ametropia and visual problems for Hong Kong Chinese and Caucasian children are different. Consequently, the referral criteria developed for Caucasian children may not be applicable to Hong Kong children. Results of our... more
The major types of ametropia and visual problems for Hong Kong Chinese and Caucasian children are different. Consequently, the referral criteria developed for Caucasian children may not be applicable to Hong Kong children. Results of our study suggested that the referral criteria for Hong Kong children should be set as hyperopia of ≥+ 2.0 D, myopia of ≥ 1.0 D, anisometropis of ≥ 1.0 D and anisometropia of ≥ 1.25 D. Sensitivity using only these criteria for abnormal refraction in identifying children with amblyopia. Esotropia, exotropia and subnormal vision (< 6/12) was respectively 100%, 84.6%, 45.2% and 95.7%. The overall sensitivity for the identification of visual problems was 86.1 % and the overall specificity was 76%. If a cover test or a Hirschberg test was introduced into the screening battery so that all the strabismic cases were identified, the overall sensitivity would increase to 98.6%.
The purpose of this study was to compare refractions measured with an autorefractor and by retinoscopy with and without cycloplegia. The objective refractions were performed in 199 right eyes from 199 healthy young adults with a mean age... more
The purpose of this study was to compare refractions measured with an autorefractor and by retinoscopy with and without cycloplegia. The objective refractions were performed in 199 right eyes from 199 healthy young adults with a mean age of 21.6 ± 2.66 years. The measurements were performed first without cycloplegia and repeated 30 min later with cycloplegia. Data were analysed using Fourier decomposition of the power profile. More negative values of component M and J0 were given by non-cycloplegic autorefraction compared with cycloplegic autorefraction (p < 0.0001). However more positive values for the J45 vector were given by non-cycloplegic autorefraction, although this difference was not statistically significant (p = 0.233). By retinoscopy, more negative values of component M were obtained with non-cycloplegic retinoscopy (p < 0.0001); for the cylindrical vectors J0 and J45 the retinoscopy without cycloplegia yields more negative values (p = 0.234; p = 0.112, respectively). Accepting that differences between cycloplegic and non-cycloplegic retinoscopy are only due to the accommodative response, the present results confirm that when performed by an experienced clinician, retinoscopy is a more reliable method to obtain the objective starting point for refraction under non-cycloplegic conditions.
Measurement of ocular wavefront aberration is becoming a popular clinical technique due to recent technical advances and an increasing awareness of its potential for practical application in the fields of surgical and optical refractive... more
Measurement of ocular wavefront aberration is becoming a popular clinical technique due to recent technical advances and an increasing awareness of its potential for practical application in the fields of surgical and optical refractive correction. In addition, information about the status of peripheral refraction determined from ocular wavefront aberrations is now being used to monitor the progression of myopia and other refractive errors in children, and as a basis for the study of the process of emmetropization. Several finite, anatomically accurate, wide-angled, model eyes have been proposed previously in an effort to produce a schematic eye that accurately reproduces vision under different practical circumstances. This paper compares these models in terms of their wavefront aberration, image quality metrics and peripheral refraction profiles and contrasts these with data from real eyes to assess their relative utility.
PURPOSE. To assess whether there are any advantages of binocular over monocular vision under blur conditions. METHODS. We measured the effect of defocus, induced by positive lenses, on the pattern reversal Visual Evoked Potential (VEP)... more
PURPOSE. To assess whether there are any advantages of binocular over monocular vision under blur conditions. METHODS. We measured the effect of defocus, induced by positive lenses, on the pattern reversal Visual Evoked Potential (VEP) and on visual acuity (VA). Monocular (dominant eye) and binocular VEPs were recorded from thirteen volunteers (average age: 28±5 years, average spherical equivalent: -0.25±0.73D) for defocus up to 2.00D using positive powered lenses. VEPs were elicited using reversing 10 arcmin checks (4 reversals/sec). The stimulus subtended a circular field of 7 degrees with 100% contrast and mean luminance 30 cd/m2. VA was measured under the same conditions using ETDRS charts. All measurements were performed at 1m viewing distance with best spectacle sphero-cylindrical correction and natural pupils. RESULTS. With binocular stimulation, amplitudes and implicit times of the P100 component of the VEPs were greater and shorter, respectively, in all cases than for monocular stimulation. Mean binocular enhancement ratio in the P100 amplitude was 2.1 in-focus, increasing linearly with defocus to be 3.1 at +2.00D defocus. Mean peak latency was 2.9 ms shorter in-focus with binocular than for monocular stimulation, with the difference increasing with defocus to 8.8 ms at +2.00 D. As for the VEP amplitude, VA was always better with binocular than with monocular vision, with the difference being greater for higher retinal blur. CONCLUSIONS. Both subjective and electrophysiological results show that binocular vision ameliorates the effect of defocus. The increased binocular facilitation observed with retinal blur may be due to the activation of a larger population of neurons at close-to-threshold detection under binocular stimulation.
PURPOSE: To demonstrate the use of the Quality of Life Impact of Refractive Correction (QIRC) questionnaire for comparing the quality of life of pre-presbyopic indi- viduals with refractive correction by spectacles, contact lenses, or... more
PURPOSE: To demonstrate the use of the Quality of Life Impact of Refractive Correction (QIRC) questionnaire for comparing the quality of life of pre-presbyopic indi- viduals with refractive correction by spectacles, contact lenses, or refractive surgery. METHODS: The 20-item QIRC questionnaire was ad- ministered to 104 spectacle wearers, 104 contact lens wearers, and 104 individuals who had undergone re- fractive
Amblyopia is a developmental ocular disease of childhood-onset which may lead to persistent sequelae into adulthood. Early detection and management of amblyopia usually result in an improved visual outcome. The purpose of this study was... more
Amblyopia is a developmental ocular disease of childhood-onset which may lead to persistent sequelae into adulthood. Early detection and management of amblyopia usually result in an improved visual outcome. The purpose of this study was to determine the prevalence and pattern of amblyopia in a rural hospital in Ghana. Clinical records of patients seen (from January 2014 to December 2018) at Westphalian Medical Center, Oyoko, Ashanti Region, Ghana, were reviewed retrospectively. Unilateral amblyopia was defined as a two-line interocular difference or more in visual acuity. Bilateral amblyopia was defined as best-corrected visual acuity (BCVA) of Snellen 6/12 or worse in both eyes, with evidence of bilateral ametropia or obstruction of the visual pathway. Following a review of 12,602 patient records, 258 cases of amblyopia were identified. The mean (±SD) presenting age of amblyopic patients was 24.3 ± 16.1 years, with a male-to-female ratio of 1:1.1. The period prevalence of amblyopia...
We defined the theoretical oxygen tension behind modern scleral contact lenses (CLs) made of different rigid gas permeable (RGP) materials, assuming different thickness of the tear layer behind the lens. A second goal was to show... more
We defined the theoretical oxygen tension behind modern scleral contact lenses (CLs) made of different rigid gas permeable (RGP) materials, assuming different thickness of the tear layer behind the lens. A second goal was to show clinically the effect of the postlens tear film on corneal swelling. We simulated the partial pressure of oxygen across the cornea behind scleral CLs made of different lens materials (oxygen permeability Dk, 75-200 barrer) and different thickness (Tav, 100-300 μm). Postlens tear film thicknesses (Tpost-tear) ranging from 150 to 350 μm were considered. Eight healthy subjects were fitted randomly with a scleral lens with a thin and a thick postlens tear layer in two different sessions for a period of 3 hours under open-eye conditions. The CLs with less than 125 barrer of Dk and a thickness over 200 μm depleted the oxygen availability at the lens-cornea interface below 55 mm Hg for a postlens tear film of 150 μm. For a postlens tear film thickness of 350 μm, n...
PURPOSE. An association between tonic accommodation, the resting accommodative position of the eye in the absence of a visually compelling stimulus, and refractive error has been reported in adults and children. In general, myopes have... more
PURPOSE. An association between tonic accommodation, the resting accommodative position of the eye in the absence of a visually compelling stimulus, and refractive error has been reported in adults and children. In general, myopes have the lowest (or least myopic) levels of tonic accommodation. The purpose in assessing tonic accommodation was to evaluate it as a predictor of onset of
