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.
Written informed consent to participate in the study
Men or women aged 18 years or older
Electroretinogram (ERG) responses compatible with the diagnosis of retinitis pigmentosa
Positive for mutation(s) in retinoid cycle related genes
Currently a smoker
Current use of vitamin A/ β-carotene supplements
Known mutations in the ABCA4 gene
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
Crossover
9-cis beta-Carotene-rich extract of Dunaliella alga
Dietary supplementParticipants will be instructed to take two soft-gel capsules twice daily (total of 4 capsules per day) for a period of 90 days. Each soft-gel capsule contains oil extraction of the alga Dunaliella, which is rich in beta-carotene (composed of approximately 70% 9-cis and 30% all-trans isomers). The capsules are manufactured by Hetchyn Ingredients Biotechnology Co., Ltd.
Placebo Corn Oil
Other interventionParticipants will be instructed to take two soft-gel capsules twice daily (total of 4 capsules per day) for a period of 90 days. The placebo capsules contain corn oil and are manufactured to be identical in appearance (size, color, and texture) to the active Dunaliella soft-gels to maintain masking.
Change in Retinal Sensitivity via Microperimetry
Microperimetry will be used to measure the mean retinal sensitivity (expressed in decibels, dB) in the central visual field. This test assesses the minimum light intensity a patient can perceive at specific points on the retina. An increase in dB indicates improved retinal function and light sensitivity.
Change in Full-Field Electroretinogram (ERG)
Measurement of the electrical response of the retina (b-wave amplitude in microvolts) to light stimuli under scotopic (dark-adapted) and photopic (light-adapted) conditions.
Change in Best-Corrected Visual Acuity (BCVA)
Measurement of visual sharpness using the ETDRS letter chart at a standard distance.
Change in Full Field Scotopic Threshold (FST)
Measurement of the lowest light intensity perceived by the patient across the entire visual field, measured in decibels (dB).
Change in Plasma beta-carotene Levels
Laboratory analysis of blood samples to measure the concentration of $\\beta$-carotene (mg/L) to correlate with clinical response and ensure washout efficiency.
Change in Pupil Response (Chromatic Pupilloperimetry)
Measurement of pupil constriction in response to focal chromatic light stimuli (red and blue light) to assess rod and cone function.
Change in Retinal Layer Thickness by SD-OCT
Use of Spectral Domain Optical Coherence Tomography (SD-OCT) imaging to monitor changes in the thickness of retinal layers (in micrometers)
Change in Ellipsoid Zone (EZ) Area (mm^2) as Measured by SD-OCT En Face Imaging
The Ellipsoid Zone (EZ) area reflects photoreceptor integrity. The total area of preserved EZ will be quantified in square millimeters (mm\^2) using semi-automated segmentation of SD-OCT volume scans. The outcome reported is the mean change in EZ area from baseline to each follow-up time point. A decrease in area represents disease progression.
Change from in Ellipsoid Zone (EZ) Length as Measured by SD-OCT
The Ellipsoid Zone (EZ) length (also known as the EZ width or trans-foveal EZ diameter) represents the horizontal extent of preserved photoreceptor integrity. This measure is quantified in micrometers (µm) or millimeters (mm) using a standardized horizontal B-scan passing through the fovea (Spectral-Domain Optical Coherence Tomography - SD-OCT). A decrease in EZ length reflects the progressive constriction of the visual field typical of Retinitis Pigmentosa. The analysis will compare the rate of change during treatment periods versus the baseline measurement and washout period.
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