Optometry and Vision Sciences - Research Publications
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ItemDoes the Swedish Interactive Threshold Algorithm (SITA) accurately map visual field loss attributed to vigabatrin?(Springer Science and Business Media LLC, 2014-12-23)BACKGROUND: Vigabatrin (VGB) is an anti-epileptic medication which has been linked to peripheral constriction of the visual field. Documenting the natural history associated with continued VGB exposure is important when making decisions about the risk and benefits associated with the treatment. Due to its speed the Swedish Interactive Threshold Algorithm (SITA) has become the algorithm of choice when carrying out Full Threshold automated static perimetry. SITA uses prior distributions of normal and glaucomatous visual field behaviour to estimate threshold sensitivity. As the abnormal model is based on glaucomatous behaviour this algorithm has not been validated for VGB recipients. We aim to assess the clinical utility of the SITA algorithm for accurately mapping VGB attributed field loss. METHODS: The sample comprised one randomly selected eye of 16 patients diagnosed with epilepsy, exposed to VGB therapy. A clinical diagnosis of VGB attributed visual field loss was documented in 44% of the group. The mean age was 39.3 years ± 14.5 years and the mean deviation was -4.76 dB ±4.34 dB. Each patient was examined with the Full Threshold, SITA Standard and SITA Fast algorithm. RESULTS: SITA Standard was on average approximately twice as fast (7.6 minutes) and SITA Fast approximately 3 times as fast (4.7 minutes) as examinations completed using the Full Threshold algorithm (15.8 minutes). In the clinical environment, the visual field outcome with both SITA algorithms was equivalent to visual field examination using the Full Threshold algorithm in terms of visual inspection of the grey scale plots , defect area and defect severity. CONCLUSIONS: Our research shows that both SITA algorithms are able to accurately map visual field loss attributed to VGB. As patients diagnosed with epilepsy are often vulnerable to fatigue, the time saving offered by SITA Fast means that this algorithm has a significant advantage for use with VGB recipients.
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ItemShort-Term Stability in Refractive Status Despite Large Fluctuations in Glucose Levels in Diabetes Mellitus Type 1 and 2(PUBLIC LIBRARY SCIENCE, 2012-12-28)PURPOSE: This work investigates how short-term changes in blood glucose concentration affect the refractive components of the diabetic eye in patients with long-term Type 1 and Type 2 diabetes. METHODS: Blood glucose concentration, refractive error components (mean spherical equivalent MSE, J0, J45), central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), axial length (AL) and ocular aberrations were monitored at two-hourly intervals over a 12-hour period in: 20 T1DM patients (mean age ± SD) 38±14 years, baseline HbA1c 8.6±1.9%; 21 T2DM patients (mean age ± SD) 56±11 years, HbA1c 7.5±1.8%; and in 20 control subjects (mean age ± SD) 49±23 years, HbA1c 5.5±0.5%. The refractive and biometric results were compared with the corresponding changes in blood glucose concentration. RESULTS: Blood glucose concentration at different times was found to vary significantly within (p<0.0005) and between groups (p<0.0005). However, the refractive error components and ocular aberrations were not found to alter significantly over the day in either the diabetic patients or the control subjects (p>0.05). Minor changes of marginal statistical or optical significance were observed in some biometric parameters. Similarly there were some marginally significant differences between the baseline biometric parameters of well-controlled and poorly-controlled diabetic subjects. CONCLUSION: This work suggests that normal, short-term fluctuations (of up to about 6 mM/l on a timescale of a few hours) in the blood glucose levels of diabetics are not usually associated with acute changes in refractive error or ocular wavefront aberrations. It is therefore possible that factors other than refractive error fluctuations are sometimes responsible for the transient visual problems often reported by diabetic patients.
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ItemInvestigation of Ocular Hemodynamics in Sturge-Weber Syndrome(LIPPINCOTT WILLIAMS & WILKINS, 2012-06)PURPOSE: Sturge-Weber syndrome (SWS) is a condition often associated with facial cutaneous angioma, vascular malformations in the brain, and ocular anomalies such as glaucoma. Reduced cerebral blood flow and ischemia have been well documented. Less is known about ocular blood flow despite the frequent associations between altered hemodynamics and the mechanisms underlying glaucomatous optic neuropathy. The aim of this research was to investigate retrobulbar hemodynamics in patients diagnosed with SWS. METHODS: The sample comprised 16 patients diagnosed with SWS and 16 age- and gender-matched normal control subjects. Four patients were diagnosed with both SWS and primary open-angle glaucoma (mean age 34.3 years; SD 26.9 years), three patients with both SWS and closed-angle glaucoma (mean age 23.3 years; SD 18.0 years), and nine patients with SWS and no glaucoma (mean age 17.2 years; SD 9.1 years). Systemic blood pressure and intraocular pressure were measured to determine the mean arterial pressure and ocular perfusion pressure. All patients and subjects underwent ultrasonography of the ophthalmic artery, central retinal artery, and short posterior ciliary arteries. RESULTS: No significant difference between groups for mean arterial pressure or ocular perfusion pressure (p > 0.05) was recorded. Participants diagnosed with SWS and primary open-angle glaucoma showed significantly reduced end-diastolic velocity (mean 0.036 m/s; SD 0.005 m/s) in their central retinal artery (p = 0.016) when compared against their age-matched normal controls (mean 0.054 m/s; SD 0.010 m/s). Participants diagnosed with SWS and no glaucoma also showed significantly reduced end-diastolic velocity (mean 0.038 m/s; SD 0.015 m/s) in their central retinal artery (p = 0.046) when compared against their age-matched normal controls (mean 0.054 m/s; SD 0.014 m/s). CONCLUSIONS: Retrobulbar hemodynamics appear to be altered in participants diagnosed with SWS irrespective of their diagnosis of glaucoma. Further research is needed to ascertain whether there are any long-term consequences of such changes to ocular physiology.