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Best disease is the most common of the bestrophinopathies.
What is Best disease?聽
Best vitelliform macular dystrophy (BVMD),聽more聽commonly聽known as聽Best Disease is the most common聽bestrophinopathy, affecting聽the聽retinal pigment epithelium聽(RPE)聽cells at the back of the eye.聽The first case of Best disease was first discovered by clinicians at Moorfields Eye聽Hospital, but it was named after the聽German ophthalmologist,聽Dr.聽Friedrich Best,聽who聽examined a large family with this condition in the early 1900鈥檚. Best disease is categorized by the appearance of a vitelliform lesion (Latin for 鈥榚gg-yolk鈥�) on the聽macula, this is usually bilateral, meaning this yellow 鈥榚gg-yolk鈥� appearance of the macula is present in both eyes of the affected individual. Best disease follows a聽dominant聽mode of inheritance and can display聽incomplete penetrance and variable expressivity, therefore even though it is a disease which is passed down genetically, there can be differences amongst those affected with Best鈥檚, even within the same family.聽聽
Best Disease聽usually聽occurs in childhood, the 鈥榚gg-yolk鈥� lesion is mostly seen between the ages of 3 to 15 years of age. There have been many studies into how common Best disease is within different populations, it is thought to affect between 1 and 9 out of every 100,000 people.聽Adult聽onset聽versions of Best disease are categorised and聽termed聽Adult vitelliform Macular Degeneration.
How does Best disease affect the eye?聽
Best disease is thought to聽progress through聽a number of聽distinct stages:
Stage I 鈥撀燩revitelliform聽stage - Vision at this early stage of Bests is normal and can be as good as 6/6 on a聽Snellen chart.聽Previtelliform聽means that it is before the classic yellow 鈥榚gg-yolk鈥� lesion formation. The RPE may be normal or there could be very subtle changes such as small structures which resemble honeycombs being present. These may appear on the retina as yellowish pigment changes centrally.聽
- Stage II 鈥� Vitelliform stage 鈥� There may be mild vision loss in this stage of disease or vision could be normal. The vitelliform stage is the classic stage in which Bests is most easily identified, by聽the presence of聽a聽yellow 鈥榚gg-yolk鈥櫬爈ike聽lesion on the macula which is usually 2-3 mm in diameter.聽聽
- Stage III 鈥撀燩seudohypopyon聽stage 鈥� There may be mild vision loss in this stage of disease. The聽build up聽of fatty聽deposits, termed聽lipofuscin,聽can lead to聽the formation of聽聽pseudohypopyon,聽where聽cells involved in inflammation build up in the聽anterior chamber聽of the eye.
Stage IV 鈥� Vitelleruptive stage 鈥� Vision will be similar to earlier stages or even be mildly decreased from previous stages. At stage IV, the 鈥渆gg-yolk鈥� lesions breaks up leading to a lesion resembling a 鈥榮crambled-egg鈥�. Irregular yellow deposits can also be observed at the back of the eye鈥�
Stage V 鈥� Atrophic stage 鈥� Vision will be greatly reduced at this stage, classically vision can range from 6/12 on a Snellen chart to 6/60 or less. Death of the RPE in the macular region can lead to the cell loss of retinal cells, including the photoreceptor cells crucial for normal vision. Scar tissue forms at the back of the eye.聽
Stage VI 鈥� Choroidal neovascularization (CNV) stage 鈥� Vision in this stage is often 6/60 or even worse. This CNV stage occurs in around 1 in 5 patients suffering from Best disease. CNV is the growth of new blood vessels from the choroidal blood supply at the back of the eye. The RPE forms a barrier between the retina and the blood supply. When the RPE cells are lost from the macular region, new blood vessels can grow in from the choroid to the retina. Often, these new blood vessels are very weak and may even break and leak, causing the build-up of fluid in the retina. A sudden change in vision could indicate CNV, which can be treated using photodynamic therapy, laser treatment or through injections of VEGF therapy.
Loss of vision in聽Bests disease聽can be slow and聽gradual, or聽can occur rapidly, and progression through the disease stages can vary in individuals and families.聽Many patients report problems聽with reading small print聽(long-sighted)聽and聽may have聽astigmatism (a 鈥榬ugby ball鈥� shape eye). One in four patients may also have multiple lesions in the retina and some of these may be away from the macula.聽The image below is a schematic of a fundus which is characteristic of a patient with Best Disease:聽
How is聽Best disease聽diagnosed?聽
Best聽disease聽can be diagnosed by聽looking for the聽characteristic聽egg-yolk-like lesions at the back of the eye聽observed in the聽vitelliform stage. Other tests are available to confirm the diagnosis.聽
聽OCT can be used to localize the lesion and look at its thickness, this may reveal elevation of the RPE with build-up of both lipofuscin and fluid.聽聽
The build-up of fatty聽deposits聽at the back of the eye can be detected using聽autofluorescent聽imaging.聽Autofluorescence聽can聽increase聽during early stages of disease.聽
An electrophysiological test, known as an聽EOG聽can be used to detect Best disease in patients. The聽EOG聽test is used聽to assess the activity聽and health聽of the RPE cells at the back of the聽eye. The test is used to calculate the聽Arden ratio, typically patients with Best disease have a ratio of 1.5 or lower, however聽EOG recordings in聽some聽patients聽can聽be normal. ERG tests, which measure retinal function, are normal in Best disease patients.
Best disease can be confirmed by genetic testing.
Are there any complications of Best disease?聽
Complications of Best聽disease聽generally聽occur聽during聽the late,聽atrophic stages of disease,聽and can聽lead聽to a rapid聽deterioration聽of聽vision.聽聽
Geographic Atrophy
Late stage disease is associated with the formation of scar tissue as the RPE cells at the back of the eye degenerate. Death of the RPE causes more widespread death of the retinal photoreceptor cells, termed geographic atrophy, leading to progressive and irreversible loss of vision.
Choroidal neovascularization (CNV)
The loss of RPE cells during late stage disease can lead to聽the formation of聽new blood vessels聽from the choroid to the retina. These聽new vessels聽can be weak,聽and聽rupture聽easily,聽leading to聽leakage聽and the build-up of fluid under the retina,聽greatly reducing vision. These聽bleeds can occur聽with聽only聽modest trauma.聽
Macular hole
The formation of a macular hole is a rare complication of Best disease. A macular hole is a tear in the macular region, which can result in a sudden decrease in vision聽in one eye.聽聽
What are the treatment options for Best disease?聽聽
There聽are聽currently no medical or surgical treatment options聽available for Best disease, or any of the聽bestrophinopathies. Scientists are currently developing聽new treatments聽and聽research聽is ongoing聽
Treatments are available for the complications of Best disease聽
Long-sightedness (hyperopia)
Hyperopia聽and astigmatism聽can be corrected using聽prescription聽glasses and contact lenses.聽聽
Choroid neovascularisation (CNV)
CNV聽can be treated by injecting anti-VEGF drugs (e.g.聽Avastin,聽Bevacizumab)聽聽into聽the聽back of the聽eye in an eye clinic. These injections can stop the growth of newer vessels, with the aim to preserve vision.聽CNV can also be treated using photodynamic therapy or laser therapy聽to shrink or seal the leaky blood vessels.聽
Macular holes
Macular holes聽can be treated聽in a surgical聽procedure.聽
Research聽into treatments for聽Best disease聽is ongoing. Patients are encouraged to visit the many聽charities and support groups for聽bestrophinopathies.聽