The goal of this observational study is to define the course of the retinal degeneration in a ZSD patient cohort. The objective of this study is to gather information so the investigators can: 1. define the course of the retinal degeneration in a ZSD patient cohort with retinal degeneration 2. define what tests best monitor the progression of the retinal degeneration 3. generate prognostic information about vision loss in ZSD. At each yearly visit, the participants will answer a functional vision questionnaire, have a physical evaluation, blood test, and participate in a variety of vision tests. The investigators will also collect pertinent medical history. Participants will travel to study site. The study will provide financial support for board and travel.