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Optometry

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Browsing Optometry by Subject "Cornea."

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    A clinical description of anterior segment variables measured using optical coherence tomography in a healthy South African young adult population: the development of normal reference intervals.
    (2018) Rampersad, Nishanee.; Hansraj Singh, Rekha.
    Background: Assessment of anterior segment variables is important to screen, diagnose and monitor ocular anomalies. Previous studies, which have focused exclusively on Caucasian and Asian sub-populations with limited attention to South African sub-populations, suggest that anterior segment variable (corneal and anterior chamber angle) measurements vary with demographic and/or ocular factors. This study investigated anterior segment variables, measured using optical coherence tomography, in a healthy South African young adult population and develop a clinical biometric guideline with normal reference intervals. Methods: A quantitative cross-sectional research design was used. Multistage random sampling was used to select 700 participants from a university population. Anterior segment variables were measured using the Fourier-domain iVue100 Optical Coherence Tomographer. The Oculus Keratograph, Goldmann applanation tonometer and Nidek US-500 ultrasonographer were used to measure corneal topography, intraocular pressure (IOP) and axial biometry respectively. Data were analysed by descriptive and inferential statistics. The reference intervals were computed using the non-parametric method recommended by the Clinical and Laboratory Standards Institute. Results: The mean age of the sample, which consisted of 350 males and 350 females, was 20.4 ± 1.8 years. The anterior segment variable measurements of the right and left eyes showed high levels of interocular symmetry with intraclass correlation coefficients greater than 0.933 and marginal mean interocular differences. Accordingly, data from only the right eyes were analysed because of the high levels of interocular symmetry. The mean central corneal thickness (CCT) was 501.91 ± 33.74 μm and significantly thinner than the mean corneal thickness in each quadrant of the paracentral and peripheral cornea (p < 0.001). The mean minimum corneal thickness was 495.73 ± 33.89 μm and 1.23% thinner than the mean CCT measurement (p < 0.001). The thinnest point on the cornea was central for 94% of participants (n = 659). The anterior chamber angle (ACA) width variables, which included the angle-opening distance taken at 500 μm (AOD500) and trabecular-iris angle (TIA), were ~553 μm and ~37° respectively. The majority of participants showed ACA width variable measurements associated with open non-occludable ACAs. The temporal ACA had slightly higher variable measurements than the nasal ACA. The corneal thickness measurements in the different zones were normally distributed (p ≥ 0.095) whereas the ACA width variable measurements were asymmetrically distributed (p < 0.001). Black participants had significantly thinner mean corneal thickness measurements than Indian participants (range between 29.10 μm between 36.38 μm) for all zones (p < 0.001). For both the nasal and temporal ACAs, Black participants had 10 μm to 22 μm lower median AOD500 measurements (p ≥ 0.031) and slightly higher (less than 1°) median TIA measurements (p ≥ 0.068). The mean corneal thickness in males were 0.35 μm to 3.93 μm thicker compared with females (p ≥ 0.137). Female participants had higher median ACA width variable measurements than male participants for both the nasal and temporal ACAs (p ≥ 0.029). Emmetropes and hyperopes had the lowest corneal thickness and ACA width variable measurements respectively. The anterior segment variables were inversely correlated with spherical equivalent refraction (p ≤ 0.003) although the correlation coefficients were relatively weak (range between 0.111 and 0.222). The CCT was the most important anterior segment variable, with a cut-off value of 527 μm, to influence IOP in the unpruned and pruned regression tree models. The other important variables included the average peripheral corneal thickness, axial anterior chamber depth and average paracentral corneal thickness. The clinical biometric guideline presents the normal reference intervals as well as the associated 95% confidence intervals for the corneal thickness and ACA width variables in a healthy South African young adult population. The normal reference interval for the CCT measurement ranged from 434 μm to 566 μm. In the present study, the mean, range and normal reference interval for the CCT measurement differed when compared with the measurements reported in other studies involving healthy African samples living within the African continent. Conclusion: This study demonstrated that anterior segment variable measurements in a South African young adult population differ when compared with studies involving Caucasian, Asian and other African sub-populations globally. Consequently, the clinical biometric guideline with normal reference intervals therein should be used by eye care personnel when examining South African individuals. Moreover, the possible influences of demographic and/or ocular factors should be considered when evaluating anterior segment variable measurements.
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    Development of an algorithmic approach for the early detection and management of keratoconus.
    (2023) Masiwa, Lynett Erita.; Moodley, Vanessa Raquel.
    Empirical evidence, supported by anecdotal evidence suggests that some Keratoconic pre-pubescent children present for their first clinical examinations with advanced signs of KC and visual impairment that cannotr be corrected with readily accessible optical aids. This is evidenced by higher prevalences of KC reported in some African communities. This negatively impacts on the lives of these children and hinders the practitioner’s capacity to successfully manage the patient and provide good functional vision, often resulting in visual impairment. The study set out to verify this observation and to offer a potential solution to the problem that is the late presentation of young subjects with KC residing in Harare. Method: A questionnaire, Visual acuity check, retinoscopy and anterior segment assessment were used to award subjects attending primary school in urban Harare aged 6-12years a keratoconus risk score as per scoring sheet developed. A comprehensive exam including refraction, slit lamp exam and keratometry were then performed on the high-risk subjects for the diagnosis of clinical KC. Topography, contrast sensitivity measurement and pachymetry map analysis were then performed for the diagnosis of pre-clinical KC. Results: 1159 subjects were recruited, 57% were female, 99% of African ethnicity and Christian background. Prevalence of clinical KC was found to be 630: 100 000 and pre-clinical KC was found to be 1360:100 000. Anterior surface abnormalities were present in 30% of the subjects considered to be high risk for the development of KC. The age range of the subjects diagnosed with clinical KC was 8-12years. VKC, reduced VA, itchy eyes and eye rubbing were the most frequently encountered symptoms. Conclusion: The odds of having KC are increased if the child is aged between 8 and 12 years and of African ethnicity, regardless of gender. Increased probability of developing KC was found in the presence of VKC, reduced VA, itchy eyes and frequent eye rubbing.. The early detection and management algorithm developed will allow for the timely diagnosis of KC and in turn offer improved prognosis as the earlier management of the condition will be possible with all treatment options still viable.