Doctoral Degrees (Ophthalmology)

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Browsing Doctoral Degrees (Ophthalmology) by Subject "Oculomotor system"

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    Congenital and genetic disruptions of human ocular motility and alignment – phenotypic / genotypic bi-directional algorithm
    (Stellenbosch : Stellenbosch University, 2019-04) Oystreck, Darren T; Meyer, David; Stellenbosch University. Facult of Medicine and Health Sciences. Dept. of Surgical Sciences: Ophthalmology
    ENGLISH ABSTRACT: Our understanding of congenital and genetic disruption to human ocular motility and alignment has expanded significantly over the past 15 years due in large part to advances in genetics. This has permitted identification of many underlying genetic causes in several conditions and provided new insight into the development and function of the oculomotor system. However, this information has also disturbed current classification systems based almost exclusively on ocular motility characteristics resulting in a knowledge gap between clinicians and researchers. As part of a team of researchers from several institutions a series of studies were conducted to better elucidate the clinical and genetic features in a large heterogeneous group of subjects with known or suspected congenital or genetic disorders affecting ocular motility and alignment. This dissertation is the outcome of this work. It also provided an opportunity to assess the value of the orthoptic evaluation by critically evaluating ocular motility and alignment patterns in this population. The main objective was to identify key patterns that can be used to predict underlying genotypes. This could provide a more rapid, cost effective approach to these disorders and better define the role for the general ophthalmologist in the investigation. This work spans over a decade and resulted in 47 publications that provide key pieces to the expanding body of knowledge in this field. Several publications served as reviews for knowledge translation for the ophthalmologist and one focuses on summarizing the orthoptic evaluation. In total 845 enrolled subjects received orthoptic evaluations. This included 40 different diagnoses and 25 different genes with mutations identified. The orthoptic information in these subjects formulated part of all research team publications. Despite only scratching the surface of the entire domain of genetic ocular motility and alignment disorders, this is likely is the largest and broadest collection of diagnoses in one report. A new classification scheme is proposed, one that is based on the underlying pathomechanisms accounting for disruption to ocular motility and alignment. A simplified clinical approach has been developed for the general ophthalmologist to utilize key orthoptic assessments as aids in appropriately classifying encountered subjects. This is important as each diagnostic category of conditions generally requires different investigations and management. This research also identified significant phenotypic overlap in genetically distinct disorders and phenotypic variability in the same genetic disorder. Therefore it is concluded that orthoptic features in isolation cannot be used to reliability predict the underlying genotype. The addition of information from other medical specialties improves this prediction. However, due to the currently small number of genotyped individuals in many of these rare disorders, more research is required before definitive genotype-phenotype spectrums can be identified. It is also emphasizes the need for standardization of the orthoptic assessment and reporting of the findings to ensure that similarities and differences be identified accurately.