Advanced Glaucoma Progression Study

Glaucoma is one of the leading causes of blindness in the world. The key to prevention of visual loss from glaucoma is early detection of the disease or its progression and timely treatment. The proposed study will investigate the role of various tests in improving detection of disease progression in advanced glaucoma. Evaluation of the peripheral field of vision (visual field examination) remains the current standard for detection of progression in glaucoma. However, there is a lot of variability or inconsistency in eyes with advanced glaucoma, which could make it difficult to detect worsening of glaucoma with visual fields. The optic nerve demonstrates significant damage in such eyes and hence oftentimes repeat imaging of the optic nerve head is not helpful for detection of change. Therefore, imaging of the central retina (the innermost sensitive tissue lining the inside of the eye), called macula, has been proposed to supplant imaging of the nerve in eyes with severe glaucoma. The macula aids in detailed central vision. Since the macular retinal neural cells are the last ones to be affected in glaucoma, measurement of macular retinal thickness could provide significant information with regard to the course of glaucoma. In the proposed study, glaucoma patients will be tested and followed with various measurements done with newer versions of optical coherence tomography (OCT) imaging and visual field machines. The patients will undergo repeat imaging and visual field testing every 6 months over the course of 5 years. Rates of change will be estimated. We will explore if changes in various outcome measures derived from imaging are correlated with the corresponding visual field changes in glaucoma, and whether the former can be used as an alternative method for detecting simultaneous or subsequent glaucoma progression. The hypothesis for this proposed research is that macular OCT parameters are valid structural measures that can be used especially in advanced disease to follow the course of glaucoma.

Glaucoma is a major public health issue worldwide and manifests clinically as a chronic progressive optic neuropathy with concomitant visual field (VF) loss. Glaucoma can cause significant visual disability and decreased quality of life (1). Based on WHO's report in 2002, glaucoma is the second cause of blindness. The key to prevention of visual loss from glaucoma is early detection of the disease or its progression and timely treatment. Glaucoma can be quite advanced at the time of initial detection. The prevalence of advanced glaucoma at the time of diagnosis varies but can be quite high. For example, the average VF mean deviation (MD) in patients diagnosed with glaucoma in the Los Angeles Latino Eye Study was -9.6 dB (2), which represents moderately advanced to severe glaucoma. Detection of progression in advanced stages of glaucoma continues to be challenging. Visual field examination remains the gold standard for detection of progression in advanced glaucoma. However, long-term VF variability or noise in such eyes is significant, which could confound detection of change. The optic nerve head and peripapillary retinal nerve fiber layer (RNFL) demonstrate significant damage in such eyes and hence are not helpful for detection of change. About 50% of retinal ganglion cells (RGCs) are located within 4-5 mm of the macular center (3). Since the macular RGCs are the last ones to be affected in glaucoma, measurement of macular retinal thickness or retinal sublayers could provide significant information with regard to the course of advanced glaucoma.

The macular retinal sublayers can now be measured with reasonable accuracy with SD- OCTs. There is some evidence that measurement of the macular ganglion cell complex (GCC, combined thickness of RNFL, RGC and inner plexiform layer or IPL), or macular retinal thickness or volume may detect early glaucoma with a performance that approximates that of circumpapillary RNFL thickness measurements (4,5). In addition, such macular measurements have proved to be very reproducible (4,6). Given this excellent reproducibility, macular outcome measures would be the main candidates for following glaucoma eyes with advanced damage, in which the macular region is essentially the only retinal area with residual RGCs.