Forster-Fuchs' Retinal Spot

Synonyms: Forster-Fuchs spot, Fuchs' retinal spot, disciform degeneration in myopia and choroidal neovascularisation in myopia.

Myopia ('short-sightedness') arises as a result of a high axial length of the globe (i.e. a long globe as measured from front to back) - see our record on Refraction and Refractive Errors for more details. In some highly myopic patients, the axial length never stabilises, a condition known as progressive myopia.

High myopia (6 dioptres or more) or progressive myopia are conditions prone to degenerative changes characterised by pale, well circumscribed, tessellated patches of chorioretinal atrophy both centrally and peripherally. These areas are prone to breaks in one of the retinal layers - the Bruch's membrane - resulting in cracks appearing throughout these lesions (like lacquer cracks). Subsequent neovascularisation and macular haemorrhage lead to a pigmented scar known as the Forster-Fuch spot. This raised, pigmented, circular lesion develops after the macular haemorrhage has been absorbed.²

Other changes include a tilted disc with associated atrophy, early age posterior vitreous detachment, zonular dehiscence (i.e. the zonules holding taut the capsular bag containing the crystalline lens) and pigment dispersion syndrome.

Forster described subretinal neovascularisation in severely myopic eyes in 1862 and Fuchs described a pigmented lesion at or near the fovea in 1901. They are both part of the same process.

• The prevalence of progressive myopia shows geographical variation (e.g. it is high in Spain and in Japan) but generally, it is thought to occur in 1-10% of myopic eyes.¹
• Up to one third of severely myopic eyes can show degenerative changes.³
• It can strike at any age but it is a very significant cause of blindness in young people in developed countries. A study in Australia found the spots in 3 of 3654 elderly people, giving a prevalence of 0.1% in this age group.⁴

This is a condition seen in high myopia. There may be genetic and environmental influences (excessive near work) contributing to the myopia. Other associations with myopia include:¹

• Stickler's syndrome
• Marfan's syndrome
• Ehlers-Danlos syndrome
• Down's syndrome
• Gyrate atrophy of the retina
• Congenital rubella
• Albinism

Symptoms⁵

• Presentation is with deteriorating vision (increasing myopia).
• There may also be complaints of visual distortion with wavy lines (metamorphopsia).
• Central or paracentral scotoma.
• Impaired colour vision.
• Prolonged recovery from light stress.

Signs

• Ability to read the Snellen chart may deteriorate by 2 lines or more in a fairly short space of time.
• The Forster-Fuchs spot may be seen near the fovea but there are wide variations in the appearance.

• Age-related macular degeneration
• Diabetic retinopathy
• Presumed ocular histoplasmosis syndrome
• Trauma
• Angioid streaks

Fluorescein angiography shows subretinal neovascularisation from the choroid as the basic underlying disease in most cases.⁶

Drugs

Pharmacological treatment is a new area with studies just emerging now. Intravitreal bevacizumab is the most recent candidate drug.⁷ This needs to be given every three months (the invasive nature of intravitreal injections means there are risks of complications) but a recent 12-month prospective study has shown some promising results so far - all be it on a very small number of eyes.⁸

Surgical

Conventional treatments of laser photocoagulation or surgical extraction of the area of neovascularisation have had limited effectiveness, partly due to the limitations of not being able to laser over the foveal area (this destroys it and the sight it imparts). Newly developed treatments such as foveal translocation or photodynamic therapy have had favourable results in the short-term,⁹ particularly in the younger patient presenting with larger lesions but with a better initial visual acuity.¹⁰ More RCTs are needed.

A vitrectomy may be carried out to prevent a particular type of PVD which affects these eyes, from leading to a traction maculopathy.¹¹ Surgical excision of subfoveal choroidal neovascular membranes in high myopia in a study brought improvement of visual acuity of at least 2 lines in 45% and no change in 37%.¹² Another trial had similar results¹³ with the visual acuity improved by 2 or more Snellen lines in 39%, decreased in 35% and remained unchanged in 26%.

Without treatment atrophy occurs around the area and prognosis is very poor.⁹ The new vessels cause traction on the retina which can lead to a retinal detachment. These patients are also at greater risk of developing macular holes.^11,14

A study from Moorfields in 1983¹⁵ showed a generally poor prognosis without intervention with 43% of the patients losing 2 or more lines of vision, while 60% were less than or equal to 6/60 at last follow-up. There was a direct relationship between visual acuity and the distance of the neovascular tissue from the fovea, and an inverse relationship between acuity and the size of the lesion. There seems to be a short neovascular growth phase, with early visual loss.

Older patients tend to have a poorer outcome than younger ones.¹⁶

Optical coherence tomography³ can detect this at its early stages so that intervention may take place.