General Diagnostic Considerations
Hereditary diseases of the eye have bilateral symmetric involvement, with rare exceptions. If ocular involvement is unilateral, other causes—such as birth defects, intrauterine or antenatal infections, or inflammatory diseases—should be considered. Because retinal degenerations can also occur as part of a systemic disorder, obtaining a thorough medical history is crucial (see Chapter 14), as is ruling out any reversible or treatable cause of retinal dysfunction, such as vitamin A deficiency, autoimmune disorders, or paraneoplastic or infectious retinopathy.
Clinical diagnostic evaluation, assessment of disease severity, and monitoring the progression of chorioretinal dystrophies usually involve some combination of electroretinography, fundus autofluorescence, optical coherence tomography (OCT), and perimetric testing. Several photoreceptor dystrophies have typical phenotypes, such as the deep retinal white dots or flecks in retinitis punctata albescens (Fig 13-1), choriocapillaris atrophy in choroideremia (CHM), retinal thickening and loss of laminations resulting from mutations in CRB1, crystalline deposits associated with Bietti crystalline dystrophy (CYP4V2), or the preserved para-arteriolar RPE in CRB1-related retinopathy. Distinctive phenotypes are the exception, however, and in most cases of photoreceptor dystrophy, there are diffuse pigment epithelial changes that are secondary effects of the diffuse photoreceptor degeneration.
Generally, panretinal dystrophies or degenerations of the RPE and retina are divided into 2 groups: (1) nonsyndromic retinopathies and (2) syndromic retinopathies. The term nonsyndromic panretinal dystrophies refers to hereditary disorders that diffusely involve photoreceptor and pigment epithelial function; these conditions are characterized by progressive visual field loss, central vision loss, and abnormal electroretinogram (ERG) responses. The disease process is confined to the eyes and is not associated with other systemic manifestations. In syndromic (secondary) panretinal dystrophies, the retinal degeneration is associated with single– or multiple–organ system disease, such as hearing loss (Usher syndrome) or multisystem disorders (see Chapter 14). Occasionally, when the etiology is unknown and no associated disease is present, the term pigmentary retinopathy is used to describe the disorder.
Figure 13-1 Color fundus photograph of a patient with retinitis punctata albescens, showing numerous deep retinal white dots.
(Courtesy of John R. Heckenlively, MD.)
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.