Outer retinal layer thickness predicts visual acuity in diabetic macular oedema
Diabetes mellitus is a common health problem in developed countries, with diabetic macular oedema (DMO) being a major cause of visual loss. A variety of treatment modalities for DMO are available including laser, steroid and intravitreal anti-vascular endothelial growth factor (anti-VEGF) agents.
Introduction
Diabetes mellitus is a common health problem in developed countries, with diabetic macular oedema (DMO) being a major cause of visual loss.1 A variety of treatment modalities for DMO are available including laser, steroid and intravitreal anti-vascular endothelial growth factor (anti-VEGF) agents.2-6
Evaluating DMO with OCT scans
Over the past 10 years, optical coherence tomography (OCT) scans have been used to provide a quantitative assessment of DMO and to evaluate the efficacy of treatment as it provides a fast, objective and non-invasive way of detecting structural changes.7 The correlation between visual acuity and OCT-measured variables, however, has not yet been well established. Some reports of OCT-measured macular changes show a correlation with vision, but several studies have had conflicting results.7-11
Retinal microstructures can now be seen, as advances in OCT technologies have led to faster scanning and higher axial resolution. Therefore, we can study morphological changes in the outer retinal hyper-reflective bands, specifically the inner segment/outer segment (IS/OS) junction, and measure the length of the photoreceptor outer segment (PROS).
Both IS/OS integrity and PROS length have been reported to be indicators of visual acuity in DMO and other diseases. 12-13
Forooghian et al measured the distance between the IS/OS junction and RPE layer to approximate the PROS length and showed that vision correlated better with PROS length than with macular thickness in DMO.13
The inner segment of photoreceptor, however, is also important for vision because it contains mitochondria and provides energy for the phototransduction process.
A study was therefore designed to measure the distance between the retinal pigment epithelium (RPE) and ELM to approximate the length of inner and outer segments of photoreceptors, and to determine its correlation with visual acuity in patients with DMO.14
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