Abstract

A 30 year male came to opd with complain of gradual, painless diminution of vision in both eyes, more in right eye than left. On examination best corrected visual acuity in right eye was 4/60 and left eye was 6/36. Both eye anterior segment was normal. Both eyes fundus examination showed yellowish colour, well delimited, about one disc diameter in size involving macula.

Introduction

The occurrence of heredo macular dystrophy in very young persons, sometimes considered congenital and usually accepted as appearing before the age of 7, was first described by Best (1905) who described a family of 59 members.

The lesion was round to oval and well delimited, covering macula or surrounding area. Zanen and Rausin termed it vitelliform cyst but in view of ophthalmoscopic appearance of cyst is deceptive and the name was subsequently changed to vitelline disc (Zanen and Harmans, 1961).

Case Report

A 30 year male came to opd with complain of gradual, painless diminution of vision in both eyes, more in right eye than left. There was no history of any systemic illness; no history of using spects. Family history was not significant.

On examination best corrected visual acuity in right eye was 4/60 and left eye was 6/36. Both eye anterior segment was normal. Pupils were briskly reacting to light. IOP was 17.3 mmHg in both eye. Both eyes fundus examination shows yellowish colour, well delimited, about one disc diameter in size involving macula.

On investigation, fundus fluorescence angiography showed blockage of choroidal fluorescence by lesion (Fig. 1 a and b). ERG was normal, EOG shows decrease Arden ratio (1.1).

Thus these finding went in favour of Best vitelliform macular dystrophy.

Case Report

A 30 year male came to opd with complain of gradual, painless diminution of vision in both eyes, more in right eye than left. There was no history of any systemic illness; no history of using spects. Family history was not significant.

On examination best corrected visual acuity in right eye was 4/60 and left eye was 6/36. Both eye anterior segment was normal. Pupils were briskly reacting to light. IOP was 17.3 mmHg in both eye. Both eyes fundus examination shows yellowish colour, well delimited, about one disc diameter in size involving macula.

On investigation, fundus fluorescence angiography showed blockage of choroidal fluorescence by lesion (Fig. 1 a and b). ERG was normal, EOG shows decrease Arden ratio (1.1).

Thus these finding went in favour of Best vitelliform macular dystrophy.

Discussion

Best Vitelliform Macular Dystrophy

This is an autosomal dominant disease that results in bilateral vitelliform (egg-like) lesions in the macula. This disease is caused by mutations in the VMD2 gene that encodes a chloride channel in the basolateral membrane of the retinal pigment epithelium (RPE), resulting in lipofuscin deposits in the RPE layer. The defective chloride channels result in an abnormal electrooculogram (EOG), i.e. low Arden ratio = light peak/dark trough. Patients will have bilateral, symmetric vitelliform lesions. Visual acuities are usually remarkably better than expected for patients with large macular lesions. A pseudohypopyon (aqueous-lipid fluid level) can be seen in the above lesions.

Best lesions may be associated with choroidal neovascular membranes and may have sub-retinal haemorrhage. Haemorrhage may also occur after minor globe trauma. The natural history is full recovery of vision after haemorrhage; thus, sub-foveal surgery is not indicated because patients who have undergone surgery do much worse than patients who are allowed to heal without surgical intervention. Visual potential is good. According to Dr. Edwin Stone, 95% of Best dystrophy patients will have vitelliform lesions by age 40, and 75% of Best dystrophy patients will have driving vision at age 60. Without a family history, only 25% of patients will have a mutation. The other patients will have another retinal dystrophy, e.g., pattern dystrophy (RDS gene), cuticular drusen, pigment epithelial detachment, central serous retinopathy, etc.

Fig. 1a : Best vitelliform macular dystrophy.	Fig. 1b

Symptoms

• Mild vision loss in the early stages.
• Moderate vision loss in the late stages.
• May be symptomatic, but most patients are discovered on routine examinations.
• May be associated with choroidal neovascular membrane (CNVM).
• Sub-retinal haemorrhage may occur with mild ocular trauma.

Sign

• Depending upon stage
• Stage 0 (Previtelliform) : Normal fundus with subnormal EOG
• Stage 1 : Pigment mottling at macula
• Stage 2 (vitelliform) : round egg yolk(sunny side up)
• Stage 3 (pseudo hypopyon) : part of lesion absorbed
• Stage 4 (vitelliruptive) : egg yolk begins to break up(scrambled egg)

Treatment

• Treat associated CNVM.
• Genetic testing
• Visual potential is usually very good.
• Avoid sub-foveal surgery because outcomes can be poor.

Differntial Diagnosis

• Pattern Dystrophy
• Central Serous Retinopathy (CSR)
• Pigment Epithelial Detachment (PED)
• North Carolina Macular Dystrophy

Bibliography

1. Allikmets R, Seddon JM, Bernstein PS, et al. Evaluation of the Best disease gene in patients with age-related macular degeneration and other maculopathies. Hum Genet 1999; 104 : 449-53.
2. Bascom RA, Liu L, Chen J, et al. A candidate gene for autosomal dominant retinitis pigmentosa (ADRP), Usher syndrome type 1, and Best vitelliform macular dystrophy. (Abstract). Am J Hum Genet 1992; 51 (suppl.) : A6.
3. Best F. Ueber eine hereditaere Maculaaffektion. Z Augenheilk 1905; 13 : 199-212.
4. Braley AE. Dystrophy of the macula. Am J Ophthal 1966; 61 : 1-24.
5. Braley AE, Spivey BE. Hereditary vitelline macular degeneration: a clinical and functional evaluation of a new pedigree with variable expressivity and dominant inheritance. Arch Ophthal 1964; 72 : 743-62.
6. Brecher R, Bird AC. Adult vitelliform macular dystrophy. Eye 1990; 4 : 210-5.

*Associate Professor; **Resident, Department of Ophthalmology, TNMC and BYL Nair Hospital, Mumbai - 400 008.