TO Yuen Ying Elaine
- MSc, Clinical Nutrition (Med Sci), University of Glasgow
- BSc(Hons), Biomedical Sciences, Glasgow C University
- Retinal nerve fiber layer imaging with spectral-domain optical coherence tomography
- Apps in mobile devices for visual field testing; quality of life in glaucoma patients
- To E, Yu M, Weinreb RN, Ye C, Liu S, Lam DSC, Leung CKS. Retinal nerve fiber layer imaging with spectral-domain optical coherence tomography – agreement with optic disc photography for measurement of RNFL defects. Ophthalmology 2011.
- Ye C, To E, Weinreb RN, Yu M, Liu S, Lam DS, Leung CK. Comparison of retinal nerve fiber layer imaging by spectral domain optical coherence tomography and scanning laser ophthalmoscopy. Ophthalmology 2011; 118:2196-202.
- Retinal Nerve Fiber Layer Imaging with Spectral-domain Optical Coherence Tomography (OCT) – A Review of the Cirrus HD-OCT, To, E, Lam, D. S. C., Leung, C. K. S. US Ophthalmic Review, 2011,4(1): 12-6.
(1) Retinal Nerve Fiber Layer Imaging with Spectral-Domain Optical Coherence Tomography- Agreement with Optic Disc Photography for measurement of RNFL Defects
Analysis of the OCT RNFL thickness deviation map could reveal additional RNFL changes not visible in optic disc photographs. A much more extensive RNFL thinning could be evident in OCT before it can be detected with optic disc photography. Although RNFL thinning measured by OCT extended beyond the boundary of RNFL defects visualized in optic disc photographs, the degree of thinning was not homogenous within a defect. There are regions with different gradients of RNFL thinning within a single defect. Following regional RNFL changes longitudinally is important to better understand the evolvement of RNFL defects in glaucoma.
Figure 1. Polar plots showing the frequency distribution for angular width of RNFL defects measured with optic disc photographs (A) and Cirrus HD-OCT RNFL thickness deviation map (B, RNFL defects in red pixels; C, RNFL defects in red and yellow pixels).
(2) Comparison of Retinal Nerve Fiber Layer Imaging by Spectral Domain Optical Coherence Tomography and Scanning Laser Ophthalmoscopy
The RNFL thickness deviation maps were aligned and overlaid with the corresponding CSLO RNFL photographs. The area and the angular width of RNFL defects from the corresponding retinal regions in the CSLO RNFL photographs and the OCT RNFL thickness maps were measured and compared. Their agreement was analyzed with the Bland-Altman plot. Bland-Altman plots revealed that a larger RNFL defect was associated with a greater difference in angular width between OCT and CSLO RNFL photography measurements.
Figure 2. The RNFL thickness deviation maps (50×50 pixels) generated by the OCT revealed the locations of abnormal RNFL thicknesses with abnormal pixels denoted in red (RNFL thickness less than the lower 99% normal distribution) or yellow (RNFL thickness less than the lower 95% normal distribution).
(3) Studying the quality of life in glaucoma patients and its significance with disease progression
Obtaining a visual field exam typically involves large and expensive visual field screening devices. In the current market there are a few apps within reach that can be downloaded and ready available to carry out visual field testing just about anywhere in the world. However, most of these apps show a high rate of false-positive results for normal patients. Although most apps can detect moderate or advanced glaucoma, the patient’s quality of life (QOL) may be affected from the beginning as early signs of glaucoma damage are relatively asymptomatic. A left eye with inferior loss can compensate a right eye of superior field loss. Therefore, visual field defects will not be clearly visible when viewed with both eyes due to defects overlapping.
Figure 3. These images represent what a scene may look like to someone with different visual field defects
Clinical parameters have provided strong evidence and reproducible measurements of structural and functional damage of the optic nerve. Visual field loss can influence daily activities of glaucoma patients such as walking, adjusting from a light to dark environment, performing daily household chores. We are currently designing and incorporating early QOL assessments in glaucoma patients that will provide us an insight on how quality of life affects various disease stages.