Dystrophies

Fundus examination

Typical findings of RP are pallor of the optic nerve, vascular narrowing, and generalized RPE diffuse moth-eaten pattern that starts with a gray discoloration and depigmentation of the RPE and migration of RPE within the retina creating a bone spicule pattern. Typically, the fovea is not involved in the early stages, and patients may preserve central visual acuity. However, the presence of concurrent vitreous opacities, cystoid macular edema, or epirretinal membrane has been described, involving the central visual acuity ( Fig. 5.1 ).

Fundus autofluorescence

The affected areas in the periphery show a mottled pattern of hypopigmentation. This pattern is surrounded by a hyperreflective zone both in the periphery and also in the macula demarcating the involved retina and the preserved retina. Macular changes could be very useful to differentiate foveal sparing or fovea-involving ( Fig. 5.1 ).

Optical coherence tomography

The optical coherence tomography (OCT) scans in RP are characterized by a progressive loss of the ellipsoid zone of the inner segments of the photoreceptors and the external limiting membrane starting at the peripheral retinal and progressing centripetally through the fovea. Progressive photoreceptor loss is subsequently reflected by a reduced thickness of the outer nuclear layer (ONL) (nuclei of photoreceptors) and outer photoreceptor-RPE complex. The analysis of these patients by OCT is helpful in order to rule out treatable findings such as cystoid macular edema and their management ( Fig. 5.2 ).

Different studies have shown a decrease on choroidal thickness in RP patients; however, other studies have shown no significant difference on the choroidal thickness compared with age-matched controls. In addition, the potential correlation of these changes on the functional outcomes of RP patients is not well understood, and some results are inconsistent.

Other features

The electroretinogram shows a marked reduction rod signal initially, then both rod and cone signals in later stages (reduced a- and b-waves); with further progression of the disease, the electroretinographic responses may be undetectable.

Usher syndrome

RP may be primary, affecting only the retina as we have described above, or could be associated with other systemic disorders. The most common association is deafness and RP, known as Usher syndrome.

Usher syndrome is defined as the combination of congenital hearing loss and RP. Usher syndrome has an autosomal recessive inheritance, and mutations in more than 15 genes have been described. Usher syndrome has been classified in three types:

• Type 1: congenital sensorineural deafness, unintelligible speech, vestibular symptoms, and early onset of the retinal changes.

• Type 2: nonprogressive deafness, absence of vestibular symptoms, and later onset of the retinopathy. This is the most common form.

• Type 3: progressive deafness starting in the 2nd–4th decades and adult-onset retinopathy. This is the rarest form.

There is only one series of small cases analyzing the changes in choroidal thickness in cases diagnosed with Usher syndrome type 2, showing a reduction on the thickness of the choroid in these patients.

Further analysis is requested in order to better understand the influence of the choroidal changes in the pathogenesis of RP and Usher syndrome. Also, the recognition of clinical features in the daily practice that may predict the functional changes that has been demonstrated would be useful in the evaluation of these diseases and the potential effects of future therapeutic approaches.