Given the task definition and input, reply with output. Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.

Abstract: Clinical and histopathological studies of two patients with distinctly different inherited juvenile retinal dystrophies indicate that the ocular defect in mitochondrial cytopathy involves the underlying pigment epithelium, whereas in the Laurence-Moon-Biedl syndrome the photoreceptor cells are primarily affected.
Case Report