Many workers have studied the ocular components which occur in eyes exhibiting differing amounts of central refractive error but few have ever considered the additional information that could be derived from a study of peripheral refraction. Before now, peripheral refraction has either been measured in real eyes or has otherwise been modelled in schematic eyes of varying levels of sophistication. Several differences occur between measured and modelled results which, if accounted for, could give rise to more information regarding the nature of the optical and retinal surfaces and their asymmetries. Measurements of ocular components and peripheral refraction, however, have never been made in the same sample of eyes. In this study, ocular component and peripheral refractive measurements were made in a sample of young near-emmetropic, myopic and hyperopic eyes. The data for each refractive group was averaged. A computer program was written to construct spherical surfaced schematic eyes from this data. More sophisticated eye models were developed making use of linear algebraic ray tracing program. This method allowed rays to be traced through toroidal aspheric surfaces which were translated or rotated with respect to each other. For simplicity, the gradient index optical nature of the crystalline lens was neglected. Various alterations were made in these eye models to reproduce the measured peripheral refractive patterns. Excellent agreement was found between the modelled and measured peripheral refractive values over the central 70o of the visual field. This implied that the additional biometric features incorporated in each eye model were representative of those which were present in the measured eyes. As some of these features are not otherwise obtainable using in vivo techniques, it is proposed that the variation of refraction in the periphery offers a very useful optical method for studying human ocular component dimensions.

The aim of this research was to determine the effect of a lutein-based nutritional supplemented on measures of visual function in normal and ARMD-affected eyes. Thirty participants were recruited to the ARMD cohort (aged between 55 and 82 years, mean ± SD: 69.2 ± 7.8) and 46 were recruited into the normal cohort (aged between 22 and 73 years, mean ± SD: 50.0 ± 15.9). Outcome measures were distance (DVA) and near (NVA) visual acuity, contrast sensitivity (CS), photostress recovery time measured with the Eger Macular Stressometer (EMS), central visual function assessed with the Macular Mapping test (MMT), and fundus photography. Reliability studies were carried out for the EMS and the MMT. A change of 14 s is required to indicate a clinically significant change in EMS time, and a change of 14 MMT points is required to indicate a clinically significant change in MMT score. Sample sizes were sufficient for the trial to have 80% power to detect a significant clinical effect at the 5% significance level for all outcome measures in the normal cohort, and for CS in the ARMD cohort. The study demonstrated that a nutritional supplement containing 6mg lutein, 750 mg vitamin A, 250 mg vitamin C, 34 mg vitamin E, 10 mg zinc, and 0.5 mg copper had no effect on the outcome measures over nine or 18 months in normal or ARMD affected participants. The finding that nine months of antioxidant supplementation, in this case, has no significant effect on CS in ARMD-affected participants adds to the literature, and contrasts with previous RCTs, the AREDS and the LAST. This project has added to the debate about the use of nutritional supplementation prior to the onset of ARMD.

The thesis aims to define further the biometric correlates in anisometropic eyes in order to provide a structural foundation for propositions concerning the development of ametropia. Biometric data are presented for 40 anisometropes and 40 isometropic controls drawn from Caucasian and Chinese populations. The principal finding was that the main structural correlate of myopia is an increase in axial rather than equatorial dimensions of the posterior globe. This finding has not been previously reported for in vivo work on humans. The computational method described in the thesis is a more accessible method for determination of eye shape than current imaging techniques such as magnetic resonance imaging or laser Doppler interferometry (LDI). Retinal contours derived from LDI and computation were shown to be closely matched. Corneal topography revealed no differences in corneal characteristics in anisometropic eyes, which supports the finding that anisometropia arises from differences in vitreous chamber depth. The corollary to axial expansion in myopia, that is retinal stretch in central regions of the posterior pole, was investigated by measurement of disc-to-fovea distances (DFD) using a scanning laser ophthalmoscope. DFD was found to increase with increased myopia, which demonstrates the primary contribution made by posterior central regions of the globe to axial expansion. The ocular pulse volume and choroidal blood flow, measured with the Ocular Blood Flow Tonograph, were found to be reduced in myopia; the reductions were found to be significantly correlated with vitreous chamber depth. The thesis includes preliminary data on whether the relationship arises from the influx of a blood bolus into eyes of different posterior volumes or represents actual differences in choroidal blood flow. The results presented in this thesis show the utility of computed retinal contour and demonstrate that the structural correlate of myopia is axial rather than equatorial expansion of the vitreous chamber. The technique is suitable for large population studies and its relative simplicity makes it feasible for longitudinal studies on the development of ametropia in, for example, children.

The principal theme of this thesis is the in vivo examination of ocular morphological changes during phakic accommodation, with particular attention paid to the ciliary muscle and crystalline lens. The investigations detailed involved the application of high-resolution imaging techniques to facilitate the acquisition of new data to assist in the clarification of aspects of the accommodative system that were poorly understood. A clinical evaluation of the newly available Grand Seiko Auto Ref/ Keratometer WAM-5500 optometer was undertaken to assess its value in the field of accommodation research. The device was found to be accurate and repeatable compared to subjective refraction, and has the added advantage of allowing dynamic data collection at a frequency of around 5 Hz. All of the subsequent investigations applied the WAM-5500 for determination of refractive error and objective accommodative responses. Anterior segment optical coherence tomography (AS-OCT) based studies examined the morphology and contractile response of youthful and ageing ciliary muscle. Nasal versus temporal asymmetry was identified, with the temporal aspect being both thicker and demonstrating a greater contractile response. The ciliary muscle was longer in terms of both its anterior (r = 0.49, P <0.001) and overall length (r = 0.45, P = 0.02) characteristics, in myopes. The myopic ciliary muscle does not appear to be merely stretched during axial elongation, as no significant relationship between thickness and refractive error was identified. The main contractile responses observed were a thickening of the anterior region and a shortening of the muscle, particularly anteriorly. Similar patterns of response were observed in subjects aged up to 70 years, supporting a lensocentric theory of presbyopia development. Following the discovery of nasal/ temporal asymmetry in ciliary muscle morphology and response, an investigation was conducted to explore whether the regional variations in muscle contractility impacted on lens stability during accommodation. A bespoke programme was developed to analyse AS-OCT images and determine whether lens tilt and decentration varied between the relaxed and accommodated states. No significant accommodative difference in these parameters was identified, implying that any changes in lens stability with accommodation are very slight, as a possible consequence of vitreous support. Novel three-dimensional magnetic resonance imaging (MRI) and analysis techniques were used to investigate changes in lens morphology and ocular conformation during accommodation. An accommodative reduction in lens equatorial diameter provides further evidence to support the Helmholtzian mechanism of accommodation, whilst the observed increase in lens volume challenges the widespread assertion that this structure is incompressible due to its high water content. Wholeeye MRI indicated that the volume of the vitreous chamber remains constant during accommodation. No significant changes in ocular conformation were detected using MRI. The investigations detailed provide further insight into the mechanisms of accommodation and presbyopia, and represent a platform for future work in this field.

No description available.

<p><strong>ABSTRAKT</strong></p><p>Vid kataraktkirurgi är det viktigt att med stor noggrannhet kunna beräkna ögats postoperativa refraktion. För detta finns det flera olika biometriformler, varav SRK/T, Haigis och Hoffer Q har ingått i denna studie.</p><p><strong>Syfte:</strong> Att jämföra hur de tre formlerna presterar i genomsnitt när man jämför den beräknade postoperativa refraktionen med det verkliga utfallet, samt att se om det finns någon skillnad i utfallet i relation till ögats axiallängd.</p><p><strong>Metod:</strong> Data från 81 ögon erhölls från ögonkliniken i Kalmar. Alla var uppmätta med IOLMaster och hade genomgått fakoemulsifikation. Den vikbara intraokulära lins som användes var Alcons Acrysof SN60WF. Data från biometrin sattes in i var och en av de tre formlerna och beräknad postoperativ refraktion jämfördes sedan med verklig. SRK/T och Hoffer Q hade optimerade konstanter, medan Haigis tre konstanter hämtats ur publicerat material. Jämförelse gjordes även för ögon med axiallängd kortare än 22 mm och längre än 25 mm.</p><p><strong>Resultat:</strong> Ingen statistiskt signifikant skillnad i utfall mellan SRK/T, Haigis och Hoffer Q fanns generellt sett. I relation till axiallängden fanns en tendens att Hoffer Q påverkas något. För ögon längre än 25 mm fanns heller ingen statistiskt signifikant skillnad mellan de tre formlerna. I gruppen med ögon kortare än 22 mm fanns det en statistiskt signifikant skillnad mellan SRK/T och Hoffer Q respektive Haigis och Hoffer Q. Dock var urvalet av korta och långa ögon så litet att någon slutsats inte kunde dras av detta.</p><p><strong>Slutsats:</strong> Studien visar att det inte finns någon statistiskt signifikant skillnad mellan hur SRK/T, Haigis och Hoffer Q presterar i genomsnitt. Inte heller i relation till olika axiallängder kan man se någon direkt skillnad mellan formlerna.</p><p>Det verkar sannolikt att Haigis formel kommer att kunna prestera ännu bättre när dess konstanter optimerats.</p>

<p>Purpose: The aim of the study was to investigate if static retinoscopy has a higher correlation with monocular than binocular subjective refraction, and also to see if there is any difference between these results and Mohindra retinoscopy.</p><p>Methods: Retinoscopy and subjective refraction was performed on 32 adult subjects and the results from 29 of these were analysed.</p><p>Results: The statistical analyses showed that static retinoscopy has a higher correlation with monocular than binocular subjective refraction. Overall the correlation was high between all the refraction methods.</p><p>Conclusion: Static retinoscopy has a higher correlation with monocular than binocular subjective refraction in adults. Static and Mohindra retinoscopy are similar, and Mohindra retinoscopy is highly correlated with subjective refraction in adults.</p>

<p>Introduction: Research has shown that people become more myopic when performing nearwork. This phenomenon is called nearwork-induced transient myopia (NITM). Although this nearsightedness is temporary it is possible that it has an effect on individuals over time, causing permanent myopia, but from a more short-term and clinical point of view; can NITM have implications on the ordinary visual examination?</p><p>Aim: The purpose of this study was to investigate if prolonged nearwork can produce a change in the distance refraction significant enough to be measured with commonly occurring instrumentation used in clinics and if patients can be overcorrected because of this.</p><p>Methods: 23 emmetropic and myopic subjects with a mean age of 24 years were examined at two occasions; prior to and after approximately 2 hours of nearwork. The refraction was determined using a Topcon VT-10 manual phoropter and the end-point of refraction was defined using the duo-chrome test.</p><p>Results: When the data was averaged across all test subjects it revealed a statistically significant myopic refractive shift of 0.16 D. A subgroup analysis revealed an average myopic shift of 0.28 D in the myopic subjects (Student’s paired t-test; P < 0.05) and an average myopic shift of 0.05 D in the emmetropic subjects (Student’s paired t-test; P > 0.05).</p><p>Conclusion: Based on the data and results presented in this study and the results from earlier studies it is reasonable to say that there is a small risk that some patients could be overcorrected due to prolonged nearwork being performed prior to a visual examination.</p>

<p>Syfte: Syftet med studien var att undersöka myopiförekomsten i fyra städer i Nicaragua för att sedan jämföra resultatet med studier om myopiförekomst från andra delar av världen. Om resultatet skiljer mellan de olika studierna så skall dessa skillnader försöka förklaras.</p><p>Metod & material: Undersökningarna utfördes i fyra olika städer i Nicaragua av tre optikerstudenter och en legitimerad optiker. Försökspersonerna, som var mellan 6 och 95 år, fick själva uppsöka undersökningsplatserna efter det att olika organisationer spridit information om var och när undersökningarna skulle ske. En testtavla med Snellen E sattes upp på 5 meters avstånd och försökspersonerna refraktionerades binokulärt med provbåge och provglas. Sedan jämfördes resultatet med andra studier om myopiförekomst.</p><p>Resultat: Av de 1178 personerna som undersöktes så hade 73 stycken en myopi på minst -0,50 D vilket motsvarar en myopiförekomst på 6,20% hos försökspersonerna. Av de myopa försökspersonerna var 48 stycken kvinnor och 25 stycken var män. Högst myopiförekomst var det i åldersgruppen 65 år och äldre där närmare 21% var myopa. Då man jämförde myopiförekomsten i Nicaragua med andra studier fann man att den var lägre i Nicaragua jämfört med alla studier förutom två. De två studierna med lägre myopiförekomst undersökte barn mellan 5-15 år och var utförda i Nepal och Sydafrika. Störst skillnad var det mellan Nicaragua och en studie med studenter mellan 15 och 19 år från Singapore medan det var minst skillnad mellan resultatet från Nicaragua och det från en studie utförd i Ecuador med försökspersoner mellan 18 och 45 år.</p><p>Slutsats: Myopiförekomsten i den undersökta gruppen i Nicaragua var betydligt lägre än de flesta studier resultatet jämfördes med. Orsaken till detta kan vara skillnader i hur mycket närarbete försökspersonerna utför samt genetiska faktorer då myopi kan ärvas vilket ökar myopiförekomsten i vissa delar av världen.</p>

<p>Introduction: Quite new on the Swedish market are orthokeratology lenses, used for both correction and myopia control. At the moment there are 22 practitioners in Sweden fitting orthokeratology lenses and 5 of those stands for 75 % of all fittings. Measuring the intraocular pressure in the eye is an important part of an eye- examination, because high intraocular pressure can result in glaucomatous changes. When using the orthokeratology lenses the corneal thickness changes, it decreases in the central epithelium and increases in the midperipheral stroma. The corneal thickness is affecting the intraocular pressure value.</p><p>Aim: The aim of the study was to evaluate how the intraocular pressure, measured with a non-contact tonometer, changes when using orthokeratology lenses.</p><p>Method: 7 people were fitted with orthokeratology lenses. The intraocular pressure was measured before using the lenses, after the first night, after the third night and after the seventh night. 12 eyes were measured after the tenth night, because of drop- out of two eyes.</p><p>Result: Already after the first night a significant decrease in the intraocular pressure occurred with 1, 34 mm Hg (p= 0,049). Day ten the intraocular pressure had an average decrease of 2, 67 ± 2, 14 mm Hg, which was a significant change (p= 0, 002 ).</p><p>Discussion: This study shows when wearing orthokeratology lenses a decrease in 2, 67 ± 2, 14 mm Hg at day 10 can be expected.</p>