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At a glance

An inherited dystrophy of the retinal photoreceptors and pigment epithelium characterized by simultaneous abiotrophic degeneration of rods and cones.

Incidence

The incidence is unknown.

Genetic inheritance

Autosomal dominant inheritance is more frequent, but autosomal recessive and X-linked transmission as well as sporadic cases have also been described. Cone Rod Retinal Dystrophy (CRD) Type I refers to an autosomal dominant inherited form of CRD that has been described in one patient only and is caused by a deletion of the 18q21.1-q21.3 segment. CRD Type II is more common, also autosomal dominant inherited and caused by mutations in the CRX (Cone-Rod Homeo Box-Containing) gene located on chromosome 19q13.33. Several (>80) genetically different types of CRD exist.

Diagnosis

The diagnosis of CRD II is based on a positive family history in association with the clinical findings (visual field defects and abnormal electroretinography).

Clinical aspects

The clinical signs are limited to the eyes with initial loss of color vision (cone-mediated; most often red-green or blue-yellow defects) and loss of visual acuity, then followed by nyctalopia (night blindness; rod-mediated) and peripheral visual field loss and early blindness. Severe photophobia and a fine nystagmus are common and chorioretinal atrophy may occur in severe cases. Examination confirms cone-rod retinal dystrophy, “Bull’s eye” macular lesions, widespread retinal pigmentation, and chorioretinal atrophy. The onset of decreased central vision with progressive shrinkage of the peripheral visual field and loss of visual acuity usually manifests before the age of 10 years. Onset of nyctalopia occurs in the third decade of life, and after the fifth decade of life, visual function is severely reduced. Unfortunately, progression to complete lack of light perception in CRD is inexorable. Besides the typical eye features described above, the patient with CRD I also suffered from hypogonadism and impaired hearing.

Precautions before anesthesia

Routine preoperative assessment is considered adequate.

Anesthetic considerations

No specific anesthetic considerations should arise from this disorder. Dealing with a blind patient who is unable to see what is happening around him/her requires more explicit explanations in general and clear warnings before any painful procedures in particular.

Pharmacological implications

None specific to this disorder.

Other conditions to be considered

  • Leber Congenital Amaurosis (Do not confuse with ☞Leber Hereditary Optic Neuropathy): This inherited degenerative disease of the retina is characterized by severely decreased vision manifesting already at birth or shortly thereafter. Other ocular anomalies may include sensory (wandering) nystagmus, amaurotic pupils, and deep-set eyes. Central nervous system anomalies have been described in some of these patients.

  • Stargardt Syndrome (Stargardt Disease; Stargardt Macular Degeneration; Familial Juvenile Macular Degeneration; Juvenile Hereditary Disciform Macular Degeneration; Fundus Flavimaculatus; Central Retinitis Pigmentosa):...

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