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Description
Myopic degeneration is a condition associated with the axial elongation of the globe and the associated thinning and stretching of the retina, retinal pigment epithelium (RPE) and choroid. Physiological myopic degeneration is the more common benign form, whereas pathological myopic degeneration is often associated with an axial length of 27mm or more, demonstrates progression over time and is potentially sight threatening.
Symptoms
Progressive increase in refractive error causes a blurring of vision. Floaters may be reported related to posterior vitreous detachment. Rarely there may be acute symptoms in relation to complications.
Signs
(a) Physiological myopia
? Peripapillary atrophy (scleral crescent) is a hallmark of myopic degeneration, arising as the retina, RPE, Bruch’s membrane and choroid are pulled away from the optic nerve head as the globe elongates
? A tilted or obliquely inserted optic disc may be present
? Posterior vitreous detachment is more common at an earlier age in myopic degeneration.
(b) Pathological myopia
? Round circumscribed areas of chorio-retinal atrophy may develop across the posterior pole, and the scleral crescent tends to widen (>1/3 of a disc diameter)
? The peripheral retina shows a higher incidence of degenerative changes including white without pressure, pavingstone degeneration and lattice. The risk of retinal holes, tears or detachment is higher
? Scleral thinning and ectasia (posterior staphyloma)
? The RPE, Bruch’s membrane and choroid are stretched and thinned, creating the appearance of the ‘tigroid’ fundus and with more evident choroidal vessels
? Lacquer cracks refer to gradual ruptures in the RPE, Bruch’s membrane and choroid. These have a similar histopathology to angioid streaks or choroidal rupture
? Fuchs’ spots are areas of RPE hyperplasia at the macula
? Choroidal neovascularisation (CNV) occurs most often near the macula. CNV is more likely in the presence of lacquer cracks, Fuchs’ spots or macular haemorrhages
? Primary open-angle glaucoma is more prevalent, perhaps due to optic nerve compromise.
Prevalence
Most (greater than 1/10) patients with myopia show physiological degeneration; in moderate to high myopia (=6.00D) pathological degenerative changes are very common.
Significance
Possible vision-threatening consequences include retinal detachment and CNV.
Differential diagnosis
Retinal degenerations and dystrophies, Angioid streaks, small choroidal ruptures.
See also
Tilted and oblique inserted discs, Posterior vitreous detachment, Choroidal neovascularisation.
Management
Additional investigations
Fluorescein angiography is used to diagnose CNV and to direct treatment. Ocular coherence tomography may also be helpful in diagnosis. Periodic visual field assessment may be indicated as the abnormal disc appearance may render glaucoma detection more complex.
Laser and incisional surgery
CNV may be treated with laser photocoagulation, photodynamic therapy or anti-angiogenic drugs delivered by injection. Retinal detachment surgery may be required.
Refractive correction
Optimise refractive correction. Contact lenses will provide a larger ocular image than spectacles for myopia >5.00D and often improve visual acuity. Refractive surgery may also be beneficial, although limitations and possible surgical complications should be considered.
Advice
While genetic effects probably predominate in pathological myopia, advice on visual hygiene issues may still be of benefit eg good lighting, near working distance preferably more than 40cm, periodic rest periods during visual tasks and optimal refractive correction. The patient should be warned of possible retinal detachment symptoms and cautioned regarding ocular trauma and the benefit of protective eyewear.
Review
Annual review in pathological myopia is recommended in relation to risk factors for glaucoma, retinal detachment or CNV complications.