Förster-Fuchs retinal spot

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

What is a Förster-Fuchs retinal spot?

A Förster-Fuchs retinal spot is a raised, pigmented, circular scar on the retina. This form of retinal scarring follows areas of degeneration and neovascularisation related to high myopia. It is named after Ernst Fuchs, who described a pigmented lesion in 1901, and Carl Förster, who described neovascularisation of the retina in 1862.

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

In patients with high myopia (6 dioptres or more) and progressive myopia, the back of the eye is prone to degenerative change characterised by pale, well circumscribed, tessellated patches of chorioretinal atrophy. These occur both centrally and peripherally, and their size is related to the degree of myopia. Breaks in one of the retinal layers - the Bruck's membrane - are prone to develop which results in cracking throughout the lesion (like lacquer cracks). Subsequent neovascularisation and macular haemorrhage lead to a pigmented scar known as the Förster-Fuchs spot. This raised, pigmented, circular lesion develops after the macular haemorrhage has been absorbed.

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

How common is a Förster-Fuchs retinol spot? (Epidemiology)

• The prevalence of progressive myopia shows geographical variation (eg it is high in Spain and in Japan). However, generally it is thought to occur in 1-10% of myopic eyes.

• Up to one third of severely myopic eyes can show degenerative changes.¹

• This 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 3,654 elderly people, giving a prevalence of 0.1% in this age group.²

Risk factors

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:

• Stickler's syndrome.

• Marfan's syndrome.

• Ehlers-Danlos syndrome.

• Down's syndrome.

• Gyrate atrophy of the retina.

• Congenital rubella.

• Albinism.

Presentation

Symptoms of Förster-Fuchs retinal spot

• Deteriorating vision (increasing myopia).

• Distortion of sight of straight lines near the fovea.

• There may also be complaints of visual distortion with wavy lines (metamorphopsia).

• Central or paracentral scotoma.

• Impairment of colour vision.

• Prolonged recovery from light stress.

• As in macular degeneration, therefore, central vision is affected.

Signs of Förster-Fuchs retinal spot

• Ability to read the Snellen chart may deteriorate by two lines or more in a fairly short space of time.

• The Förster-Fuchs spot may be seen near the fovea but there are wide variations in the appearance.

• The neovascularisation phase is short, and vision is lost early.

Differential diagnosis

• Age-related macular degeneration.

• Diabetic retinopathy.

• Presumed ocular histoplasmosis syndrome

• Trauma.

• Angioid streaks.

Investigations

Fluorescein angiography shows subretinal neovascularisation from the choroid as the basic underlying disease process in most cases.³

Management of Förster-Fuchs retinal spot⁴

Drugs

Pharmacological treatment is a new area with studies just emerging now. Intravitreal bevacizumab is the most recent candidate drug.⁵ This needs to be given every three months (the invasive nature of intravitreal injections means there are risks of complications) but a 12-month prospective study has shown some promising results - albeit on a very small number of eyes.⁶

Surgical

Conventional treatments of laser photocoagulation or surgical extraction of the area of neovascularisation have shown limited effectiveness, partly due to the limitations of not being able to laser over the foveal area (this destroys it and central vision with it). Newly developed treatments such as foveal translocation or photodynamic therapy had favourable results in the short term.⁷ but no benefit has been seen in the longer term. Anti-vascular endothelial growth factor is now considered to be the first-line treatment and current data suggests that there is a clinical response within the first 1-3 injections.⁸

A vitrectomy may be carried out to prevent the particular type of posterior vitreous detachment (PVD) which affects these eyes from leading to a traction maculopathy.⁹ In one study, surgical excision of subfoveal choroidal neovascular membranes in high myopia brought improvement of visual acuity of at least two lines in 45% and no change in 37%.¹⁰ Another trial showed similar results with the visual acuity improved by 2 or more Snellen lines in 39%, decreased in 35% and unchanged in 26%.¹¹

Complications

Without treatment, atrophy occurs around the affected area.⁷ The new vessels also cause traction on the retina which can lead to a retinal detachment. These patients are also at greater risk of developing macular holes.^{9 12}

Prognosis

A study from Moorfields Eye Hospital in 1983 showed a generally poor prognosis without intervention, with 43% of the patients losing two or more lines of vision, while 60% were less than or equal to 6/60 at last follow-up.¹³ 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.

Older patients tend to have a poorer outcome than younger ones.¹⁴

Prevention

Optical coherence tomography can detect this condition at its early stages so that early intervention may take place.¹

Dr Mary Lowth is an author or the original author of this leaflet.