Optometry
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Browsing Optometry by Author "Oberholzer, M."
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Item Open Access Amplitude of accommodation in 9 to 13 year old school children of Mankweng circuit, Limpopo province(University of the Free State, 2020-09) Mafeo, M. E.; Oberholzer, M.; Rasengane, T. A.Background: Amplitude of accommodation (AA) is the function of accommodation referred to as the dioptric difference between the far point (the eye is at rest) and near point (when the eye is fully accommodated) and is known to reduce with increase in age. To determine if an individual has low, normal or high amplitude of accommodation (AA) for his / her age, norms calculated from Hofstetterโs formulae are still used as reference all over the world. However, these norms were found to be irrelevant to Ghanaian and Swedish children. Out of the few accommodation studies conducted in South Africa, none of the studies documented the AA of learners from the Mankweng circuit, Limpopo province in South Africa. Aim of the study: The aim of this study was to investigate the AA in 9 to 13 year old school children of Mankweng circuit, Limpopo province. Method: A cross - sectional, analytical, descriptive study was conducted on 291 learners aged 9 to 13 years of age (median age = 11.3 years). Learners were conveniently selected but schools were randomised. Learners who passed visual screening tests consisting of habitual visual acuity at 6 m and 40 cm right eye and left eye (RE and LE), +2.50 D lens test at 6 m (RE and LE), prism cover test at 40 cm and direct ophthalmoscopy (RE and LE), were included in this study. One hundred and eighty - five (185) learners met the inclusion criteria and proceeded to the measurements of AA which were determined subjectively using the push - up (PU) to - blur (first data set) and pull - away (PA) to - clear (second data set) techniques, and objectively using the dynamic retinoscopy (DR) (fourth data set). The PU and the PA results were thereafter used to determine the average AA for each participant, which were regarded as the third AA measurement data set for the current participants. Results: The subjective and objective techniques of measuring AA yielded different results among the same participants aged 9 to 13 years. Dynamic retinoscopy (DR) technique measured the highest AA (median = 19.7 D), with PU (median = 14.3 D), PA (median = 13.4 D) and the average results of PU / PA techniques (median = 13.8 D) measuring lower. The median AA were reducing from 21.2 D to 18.3 D as age increased in 9 to 13 year old participants when measured with DR; from 15.5 D to 12.9 D with PU; from 14.4 D to 12.2 D with PA and from 15.0 D to 12.5 D when using the average results of PU / PA measurements. The rate at which AA changed between different age groups was found to be inconsistent. Furthermore, a significant difference existed between the AA of groups of 2 years or more apart. There was no statistical significant difference between the AA in female and male participants. The results further showed that the type of technique used to collect AA measurements, may have influenced the prevalence rate of a LOW AA. The results showed a high prevalence of LOW AA with PA technique 18.4% (CI of [13.5% to 24.6%]), followed by the average results of PU / PA techniques 12.4% (CI of [8.4% to 18.0%]) and lastly PU technique 7.6% (CI of [4.6% to 12.3%]). For the same participants, the DR technique did not measure LOW AA amongst any of the age groups. In each technique, there were outliers reported, with the majority in the 9 - year - old age group. Conclusion: The measured AA decreased with increasing age with all the techniques used, although the rate of reduction was not constant between the age groups. Furthermore, the AA between the age groups 12 and 13 years was statistically significantly different and also between the age groups of two or more years apart (e.g. 9 and 11 years). The AA in female and male participants showed no statistical significant difference. The prevalence of LOW AA determined, was higher with the PA technique as compared to the PU technique. The objective measurements were statistically significantly higher to the subjective measurements.Item Open Access Investigating contrast sensitivity as part of the assessment of visual requirements for driving(University of the Free State, 2023) Myburgh, Liani; Oberholzer, M.๐๐ฎ๐ฐ๐ธ๐ด๐ฟ๐ผ๐๐ป๐ฑ: The visual environment around a driver is altered by many factors such as weather, sun or light. Motor vehicle drivers need to be adaptable to different conditions and environments. Ninety percent of a driverโs sensory stimuli is interpreted by the visual system and a healthy functioning visual system is of utmost importance for a driver. Visual requirements for driving, currently, have no known global regulatory body and different visual requirements for drivers are found across the globe. In South Africa, two of the International Council of Ophthalmology (ICO) recommended visual requirements, are included (ICO, 2006). Current requirements include visual acuity (VA) and visual fields (VFs), but contrast sensitivity (CS) has been neglected from the requirements of vision for driving. The addition of CS is a valuable contributor to visual function, especially where different environmental conditions are concerned. Contrast sensitivity provides supplementary information about high contrast VA measurements, which may provide a better representation a driverโs vision in low light conditions such as dusk or dawn. ๐ฃ๐๐ฟ๐ฝ๐ผ๐๐ฒ: The main aim of the study was to determine if motor vehicle drivers, who obtained their driverโs licences legally by passing the visual requirements for driving in South Africa (SA), would also be able to pass the criteria of a minimum CS requirement of 1.25 Log for each eye, as per Owsley et al. (2001) and Spreng et al. (2018). The importance of a driver requiring an optimal functioning visual system, representative under all types of light and contrast conditions, becomes evident in the constantly changing environmental conditions a driver faces during the act of driving. While VA is representative of vision during high contrast conditions, CS may better represent vision in low contrast conditions. ๐ ๐ฒ๐๐ต๐ผ๐ฑ๐ผ๐น๐ผ๐ด๐: This descriptive research study design recruited 110 participants, using a convenience sampling method. All participants were in possession of a valid South African driverโs license. To investigate whether additional visual requirements, such as CS should be included in the requirements for driving in SA, the current visual requirements (VA and VFs) as well as CS as an additional requirement, were investigated for possible associations with five variables (licence type, age, gender, known/diagnosed pathology, and previous ocular surgery). ๐ฅ๐ฒ๐๐๐น๐๐: Thirteen point six percent of valid licenced drivers of the study population did not fulfil the visual requirements for their specific licence type at the time of data collection. Contrast sensitivity indicated statistically significant associations (p-value = โค 0.05) with age (p-value = 0.00 both eyes), licence type (p-value = right eyes 0.01, left eyes 0.00), known/diagnosed pathology (p-value = 0.00 both eyes), and previous ocular surgeries (p-value = 0.00 both eyes). Thus, CS measurements may be influenced by different licence types, age, known/previously diagnosed pathology, and previous ocular surgery. Arguably, if all participants were corrected to obtain a pass criterion for their specific visual requirements for driving (VA and VFs), 7.3% of these participants would still have failed the requirements if an additional minimum requirement of 1.25 Log for CS was included. ๐๐ผ๐ป๐ฐ๐น๐๐๐ถ๐ผ๐ป: Contrast sensitivity is an important and underrated visual function, especially in changing light conditions, not currently evaluated in the requirements for driving in South Africa. Contrast sensitivity is of clinical significance and may affect safe driving behaviour. The quality of vision of a driver may be compromised in the presence of reduced CS, even in the presence of good clinical VA and acceptable VFs.Item Open Access Optimal time for post-operative refraction after uneventful cataract surgery(University of the Free State, 2020-09) Biddulph, Cara; Oberholzer, M.; Kempen, E.