Cone-Rod Retinal Dystrophies

Inherited dystrophy of retinal photoreceptors and pigment epithelium characterized by simultaneous abiotrophic degeneration of rods and cones.

The incidence is unknown. Autosomal dominant inheritance is more frequent, but autosomal recessive and X-linked transmission and 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-qter segment. CRD Type II is more common, also autosomal dominant inherited and caused by mutations in the CRX gene (Cone-rod homeo box-containing gene) located on 19q13.3. However, genetic heterogeneity may exist.

The diagnosis of CRD II is based on a positive family history in association with the clinical findings (visual field defects and abnormal electroretinography). 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 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 shows cone-rod retinal dystrophy, “Bull's eye" macular lesions, widespread retinal pigmentation, and chorioretinal atrophy. The onset of decreased central vision with progredient shrinkage of the peripheral visual field and loss of visual acuity usually manifests before the age of 10 years. Onset of nyctalopia occurrs 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. CRD II is not associated with extraocular findings.

Beside the typical eye features described above, the patient with CRD I also suffered from hypogonadism and impaired hearing.

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

Leber Congenital Amaurosis (LCA) (Do not confuse with Leber Hereditary Optic Neuropathy): This is an inherited degenerative disease of the retina 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: This is the most common form of inherited juvenile macular degeneration. It is characterized by a reduction of central vision with a preservation of peripheral vision. Onset is usually before the age of 20 years. The macula presents with yellow-white spots of irregular shapes.