Vitelliform macular dystrophy (VMD) is an inherited eye condition that leads to progressive vision loss. The condition disrupts cells in a small area near the center of the retina (the macula). The macula is responsible for the sharp central vision needed for detailed tasks such as reading, driving and recognizing faces. The German ophthalmologist Friedrich Best described the condition in 1905, which is also known as Best’s disease, although there are minor differences between VMD and Best’s disease.
- Vitelliform macular dystrophy (VMD) / Best’s disease
- Types
- Eye disease epidemiology
- Causes and heredity of eye disease
- Symptoms: Decreased vision and decreasing acuity
- Diagnosis
- Treatment of eye problem
- Prognosis eye defect
- Eye disease contact groups
Vitelliform macular dystrophy (VMD) / Best’s disease
Best’s disease initially presents with normal vision. The macula, located in the retina, contains light-sensitive cells necessary for central vision. Patients with Best’s disease develop a yolk-like (= vitelliform) mass on the macula. The yellow/orange and fatty mass (= lipofuscin) manifests itself on the macula , eventually breaks and spreads through the macula. However, proper functioning of the macular cells is necessary for clear central vision (visual acuity). This implies that patients with this condition often lose central vision, have blurred vision or distorted vision (metamorphopsia). Vitelliform macular dystrophy does not affect side vision (peripheral vision) or night vision.
Retinal abnormalities are generally not present at birth. These abnormalities usually only manifest themselves from the ages of 5 to 10 years. However, the age of onset is variable. 7 to 9% of affected patients remain asymptomatic, while others have severe visual impairment.
Types
Two types of vitelliform macular dystrophy have been described. The early form (known as Best’s disease) usually appears in childhood. However, the onset of symptoms and severity of vision loss vary widely. The adult form starts later, usually in middle age, and is more likely to cause relatively mild vision loss. In both types of vitelliform macular dystrophy, the ophthalmologist sees characteristic changes in the macula during an eye examination.
Eye disease epidemiology
The condition is rare; the incidence is approximately 1/10,000. Furthermore, the disease is most common in patients of European descent, but can also be found in patients of African and Latin American descent. There is no known gender preference.
Causes and heredity of eye disease
Change in a gene
The cause of Best’s disease is mutations in the BEST1 and PRPH2 genes . BEST1 mutations are responsible for Best’s disease and sometimes for the adult form of vitelliform macular dystrophy. Mutations in the PRPH2 gene also lead to the adult form. It is striking that less than a quarter of all adult patients have mutations in the BEST1 or PRPH2 gene. In most cases, adult-onset diabetes is the cause of vitelliform macular dystrophy.
The BEST1 gene is responsible for the production of bestrophin. This protein acts as a channel that directs the movement of charged chlorine atoms (chloride ions) into or out of cells to the retina. Mutations in the BEST1 gene likely lead to the production of an abnormally shaped channel that prevents chloride flow. Researchers do not yet fully understand the correlation between these disturbed channels, the accumulation of lipofuscin in the macula and progressive vision loss.
The PRPH2 gene provides instructions for making the protein peripherin 2. This protein is essential for normal photoreceptor function (seeing light) in retinal cells. Mutations in the PRPH2 gene cause vision loss because the structures in these cells contain light pigments. It is unclear why PRPH2 mutations cause only central vision loss in patients with vitelliform macular dystrophy due to adult-onset diabetes.
Inheritance
Best’s disease is inherited in an autosomal dominant manner , meaning that one copy of the mutated gene in each cell causes the condition. Most patients diagnosed with Best’s disease have an affected parent.
The inheritance pattern of adult vitelliform macular dystrophy is uncertain. Some studies report that this occurs in an autosomal dominant pattern. However, this is not clear as many affected patients have no family history, and only a small number of affected families have been reported. Other eye problems including hyperopia, esotropia (inward strabismus with abnormal eye position), and sporadically shallow anterior chambers with glaucoma have also been reported.
Symptoms: Decreased vision and decreasing acuity
Initially, patients have normal vision, which then gradually deteriorates in childhood or early adolescence. Acuity vision is affected, but peripheral and night vision usually remains intact.
Diagnosis
Best’s disease is diagnosed by studying the fundus, making an electro-oculogram (EOG), an ERG (electro-retinogram) and/or an OCT scan. Family history is also essential. Affected patients have a typical macular lesion during the fundus examination. This looks like a yellow egg yolk. The injuries are often bilateral, but sometimes also unilateral. Furthermore, prenatal testing is possible in families in which the mutations are known. Adult vitelliform macular dystrophy resembles Best’s disease, but has a later onset, usually presents with small macular lesions, and the EOG is normal.
Treatment of eye problem
Treatment is mainly symptomatic and supportive. In everyday life, low vision aids are sometimes required. Fundus lesions or choroidal neovascularization (new blood vessels under the retina of poor quality) and hemorrhages can be treated with laser photocoagulation. Patients should stop smoking to prevent retinal neovascularization. Intravitreal injections are also possible in some patients.
Prognosis eye defect
Some people have no symptoms for their entire lives even though the disease is progressive. However, it is important to have fundus lesions regularly monitored by the ophthalmologist. Therefore, a thorough ophthalmological examination is required annually for patients of all ages. This is especially important in children to prevent the development of amblyopia (this is the medical term for “a lazy eye”). In most patients, visual acuity only deteriorates from the age of 40 to such an extent that it affects daily life.
Eye disease contact groups
An English-speaking support group for Best’s disease is available. In addition, a Dutch vitelliform macular dystrophy group has been established for Dutch-speaking patients.
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