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RETINAL DYSTROPHIES AND SYNDROMES

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Macular Dystrophies  
 

Macular dystrophies encompass a group of progressive degenerations of the retina and/or choroid affecting the macular area. They represent phenotypical...

Macular dystrophies encompass a group of progressive degenerations of the retina and/or choroid affecting the macular area. They represent phenotypical manifestations of metabolic disorders or mutations in genes expressed in the posterior retina.

They are characterized predominantly by changes in the posterior pole of genetic etiology, and are often bilateral and symmetrical. The disease usually begins at an early age, has a slow progression, and leads to decreased central visual acuity and central scotoma. At present, there are no treatment modalities to prevent disease progression.

Sorsby’s macular dystrophy is inherited in an autosomal dominant fashion, manifests usually between the 4th and 5th decades of life, and is characterized by a rapid and progressive loss of central visual acuity and peripheral visual dysfunction. The phenotype includes serous and hemorrhagic detachment of the macula, interspersed with pigmented changes.

Dystrophies of the posterior pole:

  • Adult vitelliform macular dystrophy
  • Best disease
  • Autosomal recessive bestrophinopathy
  • Central areolar dystrophy
  • Cone dystrophy (early and late-onset)
  • Pattern dystrophies (e.g. Butterfly shaped)
  • Sorsby’s macular dystrophy
  • Stargardt’s disease (and other ABCA4-related dystrophies)
  • Viteliform dystrophy
  • North Carolina macular dystrophy
  • X-linked retinosquisis

Dystrophies associated with systemic disease:

  • Bassen-Kornzweig disease (includes acanthocytosis)
  • Bardet-Biedl syndrome
  • Cockayne syndrome
  • Hallgreen syndrome
  • Laurence-Moon syndrome
  • Myotonic dystrophy (Steinert)
  • Refsun syndrome
  • Saldino-Mainzer syndrome
  • Sjögren-Larsson syndrome
Con-Rod Dystrophies  
 

Cone-Rod Dystrophies (CRD) are inherited progressive diseases that cause deterioration of the cone and rod photoreceptor cells and frequently lead...

Cone-Rod Dystrophies (CRD) are inherited progressive diseases that cause deterioration of the cone and rod photoreceptor cells and frequently lead to blindness.

The symptoms of CRD include an initial loss of color vision and visual acuity followed by nyctalopia and peripheral visual loss.

There is a wide variety of phenotypical expression of this group of disorders. Fundus findings at an early stage include a normal macula or macular RPE granularity. At later stages, the fundus picture discloses a pale optic disc, peripheral bone spicule-like hyperpigmentation and generalized atrophic changes of the peripheral retina. Attenuation of the retinal vessels evolves with disease progression.

Electroretinography shows the cone-isolated ERG waveform proportionally worse than the rod-isolated signal, and both are abnormal, progressing to complete extinction of detectable retinal activity using ISCEV guidelines.

Examples of genes associated with cone-rod dystrophies include the ABCA4 gene associated with Stargardt disease and the ALMS1 gene associated with Alström disease.

Stargardt Disease  
 

Stargardt disease is the most common juvenile macular dystrophy, generally inherited in an autosomal recessive manner, and characterized by progressive...

Stargardt disease is the most common juvenile macular dystrophy, generally inherited in an autosomal recessive manner, and characterized by progressive loss of photoreceptors in the macular region leading to loss of central vision.

Symptoms begin in the first or second decades of life, with variable progression over time, loss of central vision but with preservation of peripheral vision. Patients complain of dyschromatopsia, usually accompanied by a central scotoma.

In the initial stages of disease, the fundus is completely normal. Subsequently, changes around the fovea develop, with a granular appearance of the retinal pigment epithelium (RPE). These lesions progress to RPE atrophy and perimacular yellowish fish-tail spots typical of fundus flavimaculatus are observed. These fish-tail lesions are typically hyperautofluorescent (lipofuscin and A2E accumulation) in contrast with atrophic hypoautofluorescent regions, giving sometimes a "bull's-eye" appearance. The electro-oculography is normal in the early stages and ERG tends to be subnormal.

At present, there is no effective treatment to improve the visual deficit and prevent the progression of this disease. However, ongoing clinical trials with gene therapy and stem-cell technology may represent a great hope in the near future.

Gyrate Atrophy  
 

Gyrate atrophy is a generalized choroidal dystrophy, inherited as an autosomal recessive disease. Patients with this condition have high levels...

Gyrate atrophy is a generalized choroidal dystrophy, inherited as an autosomal recessive disease. Patients with this condition have high levels of ornithine in their plasma due to a genetic deficiency of ornithine aminotransferase

The gene coding for this enzyme has been trace to chromosome 10. Different mutations in the gene have been identified, including missense, nonsense, and frameshift mutations. Molecular defects in the pyridoxine-responsive and pyridoxine-unresponsive gene are different, and have prognostic and therapeutic implications.

Symptoms at onset are difficulty in adapting to the dark and loss of peripheral vision (similar to those of retinitis pigmentosa) since the disease initially affects the midperiphery of the retina. The fundus findings are quite unique and, typically a diagnosis can be immediately established. Visual function tests are affected in the early stages of the disease, with constriction of visual field and absent photopic and scotopic responses in electroretinogram. Photoreceptor dysfunction precedes the ophthalmoscopic evidence of the disease.

Beginning in the midperiphery there are focal areas of choroidal atrophy with well-circumscribed borders separating normal from abnormal tissue. These lesions progress toward the macula and ora serrata. These areas are initially round to oval and coalesce overtime to form large areas of atrophy, scalloped in appearance, forming a ring or a wreath (hence the term "gyrate"). The borders of the lesions show an extremely sharp demarcation from normal tissue, highlighted by hyperpigmentation. The macula is apparently the most resistant area, with central visual acuity preserved until late in the course of the disease.

Retinitis Pigmentosa  
 

Retinitis pigmentosa (RP) is a group of hereditary retinal diseases, which are characterized by progressive loss of peripheral vision, and...

Retinitis pigmentosa (RP) is a group of hereditary retinal diseases, which are characterized by progressive loss of peripheral vision, and poor night vision (nyctalopia) or poor vision in excessive light, and can later lead to loss of central vision.

There are several types of RP caused by numerous genetic mutations, whose pattern of inheritance can be dominant or recessive. RP is typically a dystrophy of photoreceptor cells in which the genetic defect causes cell death mainly in the rods and, more rarely, in the cones and the retinal pigment epithelium (RPE).

Usually the symptoms start to appear between 10 and 30 and disease progression is variable, presenting tunnel vision in the later stages.

Fundoscopy reveals RPE atrophy and hyper-pigmentation in the periphery of the retina and an average optic disc.  The presence of cells in the vitreous is common, and some patients develop cystoid macular edema. The macular pigment changes confer a “bull’s eye” appearance.

Systemic Diseases Associated with Retinitis Pigmentosa:

Systemic diseases associated with retinitis pigmentosa include a wide spectrum of disorders with diverse chromosomal, metabolic, and morphologic findings:

  • Alport syndrome
  • Bardet-Biedl syndrome
  • Kearns-Sayre syndrome
  • Mucopolysaccharidosis
  • Refsun disease
  • Usher syndrome
  • Waardenburg syndrome

All of the disorders in this group are genetically determined degenerations or dystrophies and in all of them the progressive degeneration of the photoreceptors leads to a combination of visual field defects, problems with night vision, and problems with central vision.

Usher Syndrome  
 

Usher’s syndrome is characterized by the association of retinitis pigmentosa and congenital sensorineural hearing loss, whether partial or profound. It...

Usher’s syndrome is characterized by the association of retinitis pigmentosa and congenital sensorineural hearing loss, whether partial or profound. It is classified into 4 types:

  • Type I – congenital deafness with early retinitis pigmentosa
  • Type II - congenital partial deafness and late onset of retinitis pigmentosa
  • Type III – initially normal hearing and vision that worsen with age; psychosis
  • Type IV – X-linked with retinitis pigmentosa, cataract, deafness, ataxia, and mental retardation.

Ocular symptoms include photophobia, nyctalopya, dark adaptation problems, dyschromatopsia, photopsias, and constriction of visual fields.

The classic fundus appears with dark pigmentary clumps in the periphery and perivenous areas (bone spicules).  Attenuated retinal vessels, waxy optic disc pallor, cystoid macular edema and fine pigmented vitreous cells may be found.

Molecular testing for specific forms of Usher’s syndrome will confirm the diagnosis.

Differential Diagnosis

  • Congenital hypertrophy of the retinal pigment epithelium
  • Congenital stationary night blindness
  • Vitamina A deficiency
Bardet-Biedl Syndrome  
 

Bardet-Biedl syndrome is an autosomal recessive disease characterized by pigmentary retinopathy with macular involvement (bull´s eye), polydactyly, congenital obesity, hypogenitalism,...

Bardet-Biedl syndrome is an autosomal recessive disease characterized by pigmentary retinopathy with macular involvement (bull´s eye), polydactyly, congenital obesity, hypogenitalism, mental retardation and renal abnormalities. Laurence-Moon was described a similar syndrome with spastic paraplegia and no polydactyly.

It manifests in infancy and one or more of the clinical signs may be absent, but sufferers always have retinal dystrophy with photophobia, and with a progressive decrease in visual acuity leading to severe visual loss in early adolescence.

Fundus findings range from a salt and pepper appearance to frank bone spicules, and macular changes with foveomacular hyperfluorescence on fluorescein angiography.

Senior-Loken Syndrome  
 

Senior-Loken Syndrome (or Leber Congenital Amaurosis with Nephronophthisis) is a rare ciliopathic and autosomal recessive disorder, characterized by nephronophthisis and...

Senior-Loken Syndrome (or Leber Congenital Amaurosis with Nephronophthisis) is a rare ciliopathic and autosomal recessive disorder, characterized by nephronophthisis and an early onset rod-cone retinal dystrophy of the Leber congenital amaurosis type. Retinal abnormalities manifest as congenital retinal blindness or retinitis pigmentosa. The gene most frequently mutated in Senior-Loken Syndrome is IQCB1/NPHP5.

Fundus findings are abundant pigmented spicules at the retinal periphery, associated with retinal pigment epithelium atrophy.

Clinical manifestations include cerebellar ataxia and skeletal abnormalities (cone epiphyses).