No description available.

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. / Thesis (M.Optom.)-University of Durban-Westville, 1989.

No description available.

<p>Bakgrund: Ortokeratologi är en teknik där man genom specialdesignade RGP-linser kan reducera eller helt eliminera låg och måttlig myopi och även låggradig hyperopi och astigmatism. Man sover med linserna under natten, tar ut dem på morgonen och kan sedan gå utan glasögon och kontaktlinser hela dagen med bra visus. I denna studie tas en del fakta upp om hur ortokeratologi fungerar och på vilka tekniken fungerar.</p><p>Syfte: Syftet vara att ta reda på mera om ortokeratologi då detta är en teknik på framfart. Även att jämföra undertecknads prövotid med redan gjorda studier.</p><p>Metod: I studien jämfördes en försöksperson med tidigare gjorda studier, försökspersonen använde ortokeratologilinser under 45 dagar och mätningar som togs och jämfördes var k-värde (corneas kurvatur) och fri visus (synskärpa). Mätningarna utfördes dag 1, 3, 7 och 14, sedan togs visus 1 gång i veckan för att kontrollera att den hölls stabil.</p><p>Resultat: visade att samtliga studier hade ungefär samma resultat där nästan alla försökspersoner fick bra visus under behandlingen. På försökspersonen i denna studie fungerade det också bra förutom lite inducerad astigmatism av linserna och halofenomen.</p><p>Slutsats: ortokeratologi är en väl fungerande metod om endast rätt patienter som ligger inom gränserna av synfel används. Den kräver dock mer arbete än en vanlig linstillpassning, både från tillpassaren genom täta återbesök och från patienten genom att compliance och linsskötsel är väldigt viktigt.</p><p>2008:O24</p>

M.Phil. / This study has been undertaken to determine: 1. the attributes of the competent optometric practitioner as well as 2. the teaching-learning programme to ensure competency. The teaching-learning transformation in South Africa towards outcomes-based education and training urges an investigation into the scope of optometry (what does an optometrist do?) as well as the core curriculum and learning content (what should they be taught?). The aim of this study was to investigate the attributes of competent optometric practitioners in South Africa with specific reference to the teaching-learning programme offered by Rand Afrikaans University (Johannesburg). This study suggested reflective practitioning as an alternative strategy towards the practicing of optometry. Reflective practice is a special kind of practice that involves a systematic inquiry into the practice itself, even as the practice is under way. It requires that the practitioner is open to scrutiny of beliefs, values and feelings that may be strongly held and about which there is great sensitivity. Thus, reflective practice is mindful consideration of one's actions. A study of the scope of optometry was used to compile a profile of a competent optometric practitioner. This profile is a combination of four main features, namely the competent optometric practitioner doing (practice management, etc.), the competent optometric practitioner knowing (technical and scientific skills, etc), the competent optometric practitioner being (honest and reliable, etc) and finally the competent optometric practitioner being in the world (flexible and adaptable, etc). An empirical investigation was performed by means of a structured questionnaire completed by second, third and final year optometry students at Rand Afrikaans University. The aim of the questionnaire was in the first instance to determine the respondents' perceived level of importance of 86 optometric as well as generic competencies. Secondly the questionnaire aimed to determine the perceived level of efficiency of performance, of these 86 competencies, by the students. The empirical findings were expected. The respondents made it clear that the list of competencies were very important in the practicing of optometry. Their involvement in private practices, community clinics and the Phelophepa healthtrain made their opinions valid. The implication of these findings would be the extension of the current teachinglearning programme to include more of these competencies. It was thus rather strange that these students could rate their perceived level of performance of these competencies as efficient. The exclusion of most of these competencies in the current teaching-teaming programme indicated that they could have acquired these skills and knowledge informally or that they have a vague perception of what the real execution of these competencies implies. This study recommends a review of the optometric teaching-teaming programme at RAU (as well as other institutions in SA) thereby placing a greater focus on primary health care. The review should also include relevant practice-oriented modules and offer greater scope for specialisation in the various fields that optometry render.

Pattern-related visual stress (PRVS) refers to the perceptual difficulties experienced by some individuals when exposed to high contrast striped patterns. People with PRVS were reported to have reduced sensitivity to global motion at baseline testing and the difference disappears at a second estimate. The present study was to investigate the effect of practice on global motion threshold in adults with and without PRVS. Methods: A total of 101 subjects were recruited and the Wilkins & Evans Pattern Glare Test was used to determine if a subject had PRVS. The threshold to detect global motion was measured with a random dot kinematogram. Each subject was measured 5 times at the first visit and again a month later. Receiver operating characteristic (ROC) curve analysis was applied to show the agreement between the two tests. Results: Twenty-nine subjects were classified as having PRVS and 72 were classified as normal. At baseline, the threshold to detect global motion was significantly higher in subjects with PRVS (0.832 ± 0.098 vs. 0.618 ± 0.228, p < 0.001). After 5 sessions, the difference between the normal and subjects with PRVS increased (0.767 ± 0.170 vs. 0.291 ± 0.149, p < 0.001). In ROC analysis, the area under the curve (AUC) improved from 0.792 at baseline to 0.964 at the fifth session. After a one-month break, the difference between normal and subjects with PRVS was still significant (0.843 ± 0.169 vs. 0.407 ± 0.216, p < 0.001) and the AUC was 0.875. Conclusion: The ability to detect global motion is impaired in persons with PRVS and the difference increased after additional sessions of practice.

Thesis (M.H.S.A.)--University of Michigan, 1980.

Thesis (M.H.S.A.)--University of Michigan, 1980.

Purpose. It has been documented previously that the push up (PU) and pull away (PA) methods overestimate accommodative amplitude (AA), while the minus lens-to-blur (MLB) method underestimates it. It also has been shown that the PU and PA methods produce similar results. We sought to compare data obtained from these three clinically used methods to determine AA in children and young adults with base-line normative data predicted by Hofstetter. Methods. Ninety healthy subjects (mean 11.7 years, range: 6-36 and 50F/40M), split into two groups, children (mean 9.8 years, range: 6-13 and 38F/22M) and young adults (mean 25.5 years, range: 21-36 and 16F/14M), were recruited from the patient and student populations of two schools of optometry. The subjects completed three accommodative tests presented in a random order: PA, PU, and MLB methods. Results.Findings from the MLB technique varied significantly from Hofstetter's normative values (P Conclusions. As compared with Hofstetter's normative values, this study demonstrates that the MLB technique gives a lower AA in children, while the PU and PA methods yielded consistent findings with each other and with Hofstetter's normative values. The PU method yielded values that compared closest with Hofstetter's normative data for the oldest subjects 4 tested in this study and indicates that the most consistent methods to measure AA in children is either the PU or PA methods, and the PU method for adults.

<p><strong>Purpose:</strong> The purpose of this study was to determine if there were any differences between four different target types when measuring the near point of convergence in adults.</p><p><strong>Methods and Material:</strong> The near point of convergence was measured in 35 subjects with a visual acuity of at least 1.0 (6/6) in each eye and without any strabismus. The targets used were: the tip of a pen, an accommodative target, the RAF line target and a penlight viewed through red-green filters. Both break and recovery points were assessed for the different techniques. Each target was used twice in consecutive order. The line target from RAF ruler was copied on to a small plastic ruler in order to be able to use the same ruler for measuring the results. All subjects were fitted with their best correction in the trial frame after a complete refraction. The measurements were taken to the nearest 0.25cm.</p><p><strong>Results:</strong> There was no difference found between NPC break values for the different target types in the control group. The NPC values were found to be 5.0/7.4 in the control group and 10.8/18.2 in the anomalous group. The accommodative target was found to give more remote values (11.5cm) than expected in comparison to the other targets in the anomalous group.</p><p><strong>Conclusion:</strong> In patients with normal NPC, the measurements can be taken with line target or Acc. target. Patients with receded NPC values should be evaluated with penlight and red-green glasses or at least twice with the tip of a pen. </p>