9-cis Beta-Carotene-Rich Extract of Dunaliella Alga in Retinitis Pigmentosa Patients

The goal of this clinical trial is to learn if a natural supplement called 9-cis beta-carotene (derived from the Dunaliella alga) can improve vision and retinal function in adults with Retinitis Pigmentosa. The study will also monitor the safety of the food supplement and how it affects levels of Vitamin A-related proteins in the blood. The main questions the study aims to answer are: (1) Does taking the supplement improve light sensitivity in the retina (measured by microperimetry)? (2) Does the supplement improve electrical responses in the eye (ERG) or other visual functions like contrast and color vision? (3) How do blood levels of beta-carotene and Vitamin A change during treatment? Researchers will use a crossover design. This means every participant will receive both the active supplement and a placebo (a "dummy" pill with corn oil) at different times during the study to compare the results. Participants will take two soft-gel capsules twice a day for 3 months, undergo a 6-month "washout" period where no study capsules are taken.Then they will take the opposite capsules (either the supplement or the placebo) for another 3 months. The participants will visit the clinic 4 times over the course of 12 months for eye exams, eye imaging (like OCT), and blood tests. Participants will also receive follow-up phone calls every 6 weeks to check on their progress and health.

Inclusion Criteria: 1. Written informed consent to participate in the study 2. Men or women aged 18 years or older 3. Electroretinogram (ERG) responses compatible with the diagnosis of retinitis pigmentosa 4. Positive for mutation(s) in retinoid cycle related genes Exclusion Criteria: 1. Currently a smoker 2. Current use of vitamin A/ β-carotene supplements 3. Known mutations in the ABCA4 gene 4. Active arterial disease within 3 months prior to enrolment in the study, e.g. unstable angina, myocardial infarction, transient ischemic attack, stroke, coronary artery bypass graft surgery 5. History of malignancy, excepting basal or squamous cell skin carcinoma 6. Women who are pregnant, or breast feeding, or are premenopausal but not using chemical or mechanical contraception 7. Uncontrolled hypertension, defined either as resting diastolic blood pressure \>95 mmHg (taken from the mean of 3 readings) or as resting systolic blood pressure \>180 mmHg 8. History of alcohol abuse or drug abuse or both 9. Intention to engage in vigorous exercise or an aggressive diet regimen 10. Uncontrolled endocrine or metabolic disease 11. Participation in another investigational drug study within 4 weeks prior to enrolment 12. Serious or unstable medical or psychological condition which, in the opinion of the PI, would compromise the subject's safety or successful participation in the study 13. Initiation of hormone replacement therapy or oral contraceptive therapy within 3 months prior to enrolment