optic disc drusen

Microphthalmia with Retinitis Pigmentosa

Clinical Characteristics
Ocular Features: 

A decrease in visual acuity with night blindness begins in the third decade of life.  The axial length is decreased resulting in high hyperopia.  There is diffuse scleral thickening, macular schisis of the outer retinal layers, and drusen may be present in the optic nerve.  The retinal pigment epithelium is abnormal with both pigment clumping and bone-spicule formation.  Areas of hypo- and hyperfluorescence are seen on fluorescein angiograms.  The cornea is normal-sized with shallow anterior chambers but narrow angles were not reported.  Intraocular pressures were normal.  On ERG recordings rod responses are missing while cone tracings are severely diminished. 

Systemic Features: 

No systemic disease is associated. 

Genetics

Based on consanguinity in the parents of the single family reported, this seems to be an autosomal recessive disorder.  Molecular studies confirm that the four affected sibs are homozygous for mutations in the MFRP gene (11q23) while the parents are both heterozygous.

Another disorder of small eyes but with classical findings of nanophthalmos and retinitis pigmentosa has also been described (267760) (nanophthalmos with retinopathy) and may be the same disorder especially since no molecular mutation has been identified.  

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Low vision aids may be helpful, at least in early stages of the disease. 

References
Article Title: 

Nanophthalmos Plus Syndrome

Clinical Characteristics
Ocular Features: 

This is a recently described type of nanophthalmos with characteristic clinical features plus retinal degeneration and optic disc drusen.  Hyperopia is common and, like another recessive form of nanophthalmos (267760), patients have a progressive retinal dystrophy beginning with granular and mottled RPE changes and progressing to a bone spicule pattern resembling retinitis pigmentosa.  No synechiae have been reported in this syndrome however.  Macular retinoschisis and cystic changes with reduced foveal reflexes are commonly present.  The anterior chamber and angles are narrow but no reported cases have had angle closure glaucoma such as frequently occurs in other forms of nanophthalmos (267760, 609549, 600165, 611897).  Drusen of the optic nerve head can be demonstrated by ultrasound.  Scleral and choroidal thickening are usually present.  There is progressive deterioration of photoreceptors beginning with rod dysfunction and eventually involving cones as documented on ERG recordings.  Nyctalopia and visual difficulties begin in childhood and the visual field is concentrically constricted.  Visual acuity is in the range of 20/100 to 20/200.

Systemic Features: 

No systemic abnormalities have been reported.

Genetics

This is an autosomal recessive disorder caused by mutations in the membrane frizzled-related protein coding gene MFRP (11q23) expressed in retinal tissue.  Both homozygous and compound heterozygous mutations have been described.  It seems to be allelic to another nanophthalmos condition without retinal pigmentary degeneration which is caused by different mutations in MFRP (NNO2 609549).  However, there is considerable clinical overlap of the several nanophthalmos conditions and it is possible that this is simply clinical heterogeneity within the same disease.

A syndromic form (MCOP5) of autosomal recessive microphthalmia with retinitis pigmentosa (611040) is also caused by mutations in MFRP and may be the same disorder.

For other forms of nanophthalmos see:  267760, 609549, 600165, 611897.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Angle closure glaucoma is a constant threat in some nanophthalmic conditions but has not been reported in this disorder.  Nevertheless, it may be prudent to consider prophylactic iridotomies in high risk cases.

References
Article Title: 
Subscribe to RSS - optic disc drusen