The different forms of myopic macular atrophy (META-PM classification11) have different appearances on OCT. 9 Simulations of retinal haemodynamics found that pathological alterations in eye shape equivalent to myopic eyes adversely affect the retinal vascular circulation, 10 which may affect function. 3,8 Posterior staphyloma and globe distortion also lead to reduced retinal sensitivity and visual field defects. Eyes with myopic macular neovascularisation have the least abnormal average curvature. The latter has been associated with a more conical, less spherical staphyloma shape. 7 Retinal curvature in OCT clearly relates to staphyloma shape, and increased curvature is associated with all myopic complications, with the mean curvature greatest in eyes with chorio-retinal atrophy, followed by myopic traction maculopathy. Irregular staphylomatous posterior segments (Figure 1C) have been associated with many of the manifestations of myopic maculopathy, and a correlation can be made between fundus photography, OCT profile, MRI appearance, staphyloma classification (Curtin classification), and visual acuity. There is a clear link between the degenerative shape features, their impact on retinal structure, and visual acuity Retinal myopic changes are degenerative and often affect vision later in life. Hence the macular BM area does not enlarge with myopic eye growth. BMO around the disc translates temporally with increasing myopia, contributing to the peripapillary gamma zone with associated increase in disc fovea distance. The size of the BM opening (BMO) near the optic disc enlarges as the eye elongates, whereas the distance between superior and inferior temporal arcades does not. The en face OCT, sometimes called the OCT C scan, can be very useful in mapping areas of abnormality in the posterior pole (Figure 1F and 1G). Rather than increasing their total volume, sclera and choroid thin post-equatorially with increasing myopia and age, whereas Bruch’s membrane (BM) does not. Choroidal thickness is the most significant predictor of visual acuity in high myopes in the absence of other macular disease, 6 and choroidal thinning has been used as a biomarker for myopic progression. Retinal thickness decreases markedly in the periphery with increasing axial length, while the neurosensory macula thinning is real but much more subtle. 4 While younger myopes often show little chorio-retinal pathology (Figure 1A and 1B), 5 changes in macular volume in myopia have been measured with SD OCT in pre-teens. 1–3 Like all degenerative processes, myopic pathology becomes more apparent and a greater burden with age, with changes typically appearing after the fifth decade of life. This irregularity can be seen with magnetic resonance imaging (MRI), and the increasingly irregular retinal contour of larger eyes can be quantified with OCT. Myopic eyes become both larger and more irregular in shape. The faster SS OCTs also have better resolution across the whole depth of the scan, providing greater detail of the vitreous, choroid, sclera and anatomy of staphylomata. This greater depth in particular, can be helpful in the more myopic staphylomatous eyes where it may be hard to visualise the entire macula in a conventional spectral domain (SD) OCT scan. Newer, faster, swept source (SS) OCT machines provide increased sampling size up to 16mm wide and 6mm deep. The principal limitation of OCT is the size of retina that can be sampled in a single scan. Most spectral domain (SD) OCT machines image a 6–12mm long retinal segment, with a depth of image of 2–3mm. Through imaging of the macula, disc, and mid-periphery, OCT reveals many of the pathological effects of myopia on retinal structure, function and vision. The OCT B scan (1G) is located at the horizontal marker line (blue). Identifies regions of patchy atrophy due to myopia. Post-operative image (1E), note choroidal thinning, with marginal recovery of the ellipsoid line in the post-op image, despite a good surgical result. Pre-operative image (1D), the eye required Figures 1D and 1E show myopic traction maculopathy with foveo-schisis. To the right generalised retinal thinning over diffuse choroidal atrophy. To the left outer retinal atrophy over the enlarged BM opening, and myopic choroidal thinning. Figure 1C shows a myopic staphyloma (SS OCT). Both have diffuse choroidal atrophy, but the older eye is more severely affected, with choroidal thinning, enlarged BM opening, and mild myopic traction maculopathy. Figure 1B from a 71-year-old myope, axial length 28.5mm. Figure 1A is from a 37-year -old myope, axial length 28.89mm. Myopic retinal degeneration increases with age.
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