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Optometry

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Browsing Optometry by Subject "Contact lenses."

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    The oxygen performance of a contact lens on the human eye.
    (1989) Postum, Krishnachand.; Turnbull, Duncan Kenneth.; Govinden, H. S.
    There is considerable evidence to indicate that most gas permeable contact lenses do not transmit sufficient oxygen to supply all the corneal oxygen requirement. This problem is further exacerbated by non-valid methods of characterizing the oxygen performance of such lenses. The current methods of using oxygen permeability (Dk) and oxygen transmissibility (Dk/L) as indices of oxygen performance of contact lenses is completely erroneous. Dk and Dk/L pertain to contact lens materials in flat sheet form having uniform thickness and equal diffusion path at all points on the surface. Finished contact lenses, of necessity, are curved surfaces and of varying thickness. Consequently the concept of Dk and Dk/L cannot be applied to contact lenses. To date there are no studies to determine the absolute oxygen tension under gas permeable contact lenses on the human eye. All attempts to quantify the oxygen tension under a lens have been by indirect methods or by predicting the p02 from Dk values, using mathematical equations. These results do not match the clinical findings. This study was done to show that oxygen flux through a contact lens, measured in vitro, is a better determinant of the in vivo oxygen performance of gas permeable contact lenses. A special cell was designed to measure the oxygen flux, in vitro under standardised conditions. Contact lens microelectrodes were designed to measure the oxygen tension in vivo. The data obtainedwas used to develop a model for the oxygen performance of rigid gas permeable lenses on the human eye.
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    Patterns of contact lens prescribing in KwaZulu-Natal.
    (2015) Moodley, Veni.; Khan, Naimah Ebrahim.
    Master of Medical Science in Optometry. University of KwaZulu-Natal, Durban 2015.
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    Schirmer tear test 2 and tear break-up time values in a South African young black adult population.
    (2012) Khan, Naimah Ebrahim.; Oduntan, Olalekan Alabi.
    Aim: The aim of this study was to establish normal values for Schirmer tear test (version 2) and tear break up time (TBUT) in a South African young adult Black population. Method: Following ethical approval by the biomedical research and ethics committee, KwaZulu-Natal, participants were recruited from the city of Durban in South Africa via personal invitations, poster advertisements and University of KwaZulu-Natal optometry clinic clients. McMonnies questionnaire for dry eye diagnosis was administered and those who failed were excluded from the main study. Two hundred (100 males and 100 females) participants who met the inclusion criteria were included in the study. Following a slit lamp examination of the eye, the Schirmer test was administered and the following day, the TBUT was measured. A re-test version of the two procedures were conducted one week after, at about the same time of the day for each subject. Results: The participants were aged 18-30 years, mean = 20.77 ± 2.29 years. The mean Schirmer test values for all participants (N = 200; 400 eyes) was 15.96 ± 6.86mm. The values for the males and females (200 eyes each) were 16.34 ± 6.93mm and 15.58 ± 6.81mm respectively. The mean TBUT (400 eyes) was 7.18 ± 1.89 secs. The mean values for the males and females (200 eyes each) were 6.90 ± 1.88 secs and 7.32 ± 1.67 secs respectively. A strong positive correlation (r = 0.895) and (r = 0.914) respectively was found between the right and left eyes in the two tests. Conclusion: Generally, the mean values found in this study for the Schirmer test are similar to those that have been reported in the literature. However, values for TBUT differ from the values that have been previously reported, being higher in some instances and lower in others. These findings have implications for dry eye diagnosis and also contact lens practice in South Africa.