macular dystrophy

This is a rare type of pigmentary retinopathy with few symptoms in many patients.  Pigment clumps in the form of bone spicules in a paravenous distribution appear as young as 1 year of age and may be present congenitally.  The pigment may begin peripherally and is often segmental but eventually progresses centrally along with chorioretinal atrophy involving the majority of the fundus.  For unknown reasons, males are more severely affected than females.  In one family the retinal changes were associated with hyperopia, esotropia and vitreous degeneration (cells and liquefaction).  There is considerable variation in expressivity among patients and the vision and fundus pigmentation can be highly asymmetrical in the two eyes.  ERG abnormalities likewise vary widely with decreased photopic responses in some individuals and complete lack of both scotopic and photopic responses in severely affected eyes.  Decreased night vision is not a symptom.

This is generally considered to be a stationary condition but long term follow up reveals progression of pigmentary changes, chorioretinal atrophy and increasing constriction of the peripheral visual field.  Symptoms of decreased vision may be noted as early as 3 months of age.  Some patients retain vision of 20/20 or 20/30 into midlife whereas others in the first decade already have count fingers vision.  Likewise the size of the visual field varies widely and is not correlated with age.

Only a few families have been reported.  The macular edema can be traced to retinal capillary leakage throughout the posterior pole as revealed by fluorescein angiography.  Scattered exudates and nerve fiber layer hemorrhages are sometimes seen.  Hyperopia and strabismus are often present as well.  Veils, strands, and white punctate deposits in the vitreous have been described.  Wrinkling of the internal limiting membrane may be present.  The ERG is normal except for elevated rod dark adaptation thresholds.  Light/dark ratios are abnormal on EOG testing and mild dyschromatopsia can be demonstrated.  Patients usually notice problems with their visual acuity in the second decade of life and it can drop to 20/200 at this time with progression to 2/120 - 2/200 in older individuals.  In later stages of the disease a central zone of beaten bronze macular atrophy can be seen.  Surrounding this central atrophy is often an area with pigmentary changes resembling retinitis pigmentosa which can extend into the periphery.

This would seem to be a unique disorder in spite of some similarities to retinitis pigmentosa in which macular cysts are often seen.  The clinical course is distinctly different and the presence of vitreous deposits and hyperopia also can be used as arguments for its separateness.  Molecular DNA evidence showing lack of allelism (Vida infra) is, of course the strongest evidence.

The earliest fundus findings consisting of a yellowish refractile sheen (about 1 disc diameter in size) with red fenestrations in the central macula were found in a 4 year old.  Changes in macular pigmentation were noted at the age of 16 years.  Visual acuity remains normal.  By the third decade of life an annular zone of hypopigmentation could be seen around the sheen and this gradually enlarged.  The sheen seemed to emanate below the retinal vessels but anterior to the RPE.  At the center a ‘bull’s eye’ pattern of hyperpigmentation appeared.  By the 6^th decade of life paracentral scotomas were present causing some visual disturbance.  Fluorescein angiography reveals no abnormalities in the sensory retina or retinal vasculature but an annular zone of window defects around the ‘bull’s eye’ can be seen.  The scotopic ERG can be normal while the amplitudes of the photopic ERG may show a mild reduction in amplitude and the EOG light-dark ratio can also be slightly reduced.  Mild red-green color deficits can be demonstrated.

The primary feature of this form of macular dystrophy is atrophy of the RPE and choriocapillaris centralized to the macula.  In early stages among young patients in the second decade of life, some pigment changes are seen in the parafoveal area.  Later, the central macula develops hypopigmentation followed by atrophy of the choriocapillaris.  The area is usually sharply defined but fluorescein angiography often shows multiple window defects beyond the edges.  The same region often has speckled autofluorescence.  Secondary dysfunction of the photoreceptors in this area leads to some mild degree of vision loss in adults between the ages of 30 and 60 years but this progressive disease may eventually result in legal blindness.  The ERG demonstrates a cone dystrophy. The rate of disease progression is highly variable.  Visual acuity varies considerably as does the appearance of the macula.  Older individuals may be misdiagnosed as having age-related macular degeneration. 

Patterned dystrophies of the macula are clinically heterogeneous.  It is common for different patterns to be seen among multiple members of a single family.  They can also be different in the two eyes of the same individual.  RPE changes can often be seen in the second decade of life but visual disturbances may not be noted until a decade or two later.  The process is progressive and eventually macular function is severely depressed with vision in the range of 20/200.  The pigmentary retinopathy occurs at the level of the RPE with the typical appearance of pigment but sometimes an accumulation of white or yellowish deposits is present.  The pattern of changes may appear in a configuration resembling the wings of a butterfly, hence the name.  However, vitelliform-like lesions have also been reported.  Paracentral tritan color defects have been described.

Subfoveal choroidal neovascularization can occur.

While the ERG may show some diffuse photoreceptor dysfunction in the presence of normal vision, there is little to suggest a primary rod or cone abnormality. Dark adaptation is normal.  Visual fields can reveal a small central scotoma and fluorescein angiography often shows window defects in the posterior pole. 

Granular pigmentation and a grayish coloration of the retina may be present.  The peripheral retina usually appears normal but the posterior pole and macula have pigmentary changes consisting of clumping and geographic atrophy.  Fluorescein angiography shows patchy areas of hyperfluorescence.  Patients in their 30s have been reported to have normal ERGs in one study.  Reduced acuity can be noted in the first decade but progression is slow.  Acuity levels in the 20/200 range may be seen in the fourth decade of life.