User:Dukeygooner/pathological myopia

Pathological Myopia

Pathological myopia, also known as high myopia, degenerative myopia or even malignant myopia, is a rare eye condition caused by a significant and progressive elongation of the eyeball throughout life (ref). This increased “axial length” leads to an array of secondary conditions that have the potential to severely impair sight, rarely to the extent of legal blindness or beyond (20/200 or worse in the USA). It is commonly stated that high myopia is a leading cause of blindness throughout the world (ref) but the condition is most noteworthy for the fact that visual impairment typically occurs much earlier in life when compared to other more common degenerative retina conditions such as age related macular degeneration. Age of onset of complications is usually in the third or fourth decades of life but in reality the condition is present at birth in true pathological myopes. The underlying cause of pathological myopia (and myopia in general) is still largely unknown but it is likely that environmental and genetic factors play a role (ref).

The diagnosis of pathological myopia has historically been based on axial length (>26 mm) and degree of refraction alone (>-6D to -8D) (ref). However, most patients who meet these criteria will not go onto develop true degenerative changes and therefore a diagnosis of pathological myopia should also consider the presence or absence of typical myopic changes at the posterior pole. These include a generalized retinal thinning (so-called “tigroid fundus”), lattice degeneration in the peripheral retina, lacquer cracks, tilted optic discs, optic disk atrophy, patchy RPE atrophy and posterior staphyloma (ref). Perhaps the most ominous of these is the posterior staphyloma involving the macula, a feature almost exclusive to high myopia and one which has been shown to reliably predict the degree and extent of myopic degeneration over time (ref). It is likely that a staphyloma of some degree is present at birth in most patients and progresses over time and it is thought that it is this that is the underlying cause of most of the retinal degeneration in pathological myopia.

Types of myopia

Myopia can be grouped into three general subtypes and the reader is referred to the excellent Wikipedia article on myopia for a more detailed discussion:

1)	Simple myopia 2)	Intermediate myopia 3)	High myopia

By definition, simple and intermediate myopia do not display any degree of retinal degeneration and are mainly refractive disorders which can be managed by optical correction alone, although for the purpose of this article this is somewhat an oversimplification. Nevertheless in these forms of myopia, progression typically slows or stops after the patient reaches post-puberty and does not progress any further and is not characterized by significant and relentless axial lengthening. This is a key point as high myopes demonstrate axial length progressions which are observable at any age and which may be interspersed by periods of stability.

(in progress)

Diagnosis and age of onset Pathogenesis and progression Complications Myopic CNV Posterior staphyloma