What is a clinical trial?

ClinicalTrials.gov includes both interventional studies and observational studies. They serve different purposes.

Interventional studies. In an interventional study, also called a clinical trial, researchers assign participants to receive a treatment, procedure, device, or another intervention. They then measure what happens. The treatment may be compared with standard care, an inactive treatment called a placebo (definition: An inactive treatment made to look like the real one, used in some trials so researchers can tell whether the actual treatment is responsible for any effect.), a sham procedure (definition: A procedure that mimics the steps of a real treatment, such as an injection, without delivering the experimental therapy — used for comparison in some trials.), or a group that does not receive the experimental treatment.

Observational studies. In an observational study, researchers do not assign participants to a new treatment. Instead, they collect information and follow what happens over time. For RP, these may be called natural history studies. They can help researchers understand how a particular form of RP progresses, which tests best measure changes in vision, and how future treatment trials should be designed.

Participation begins before anyone receives a study treatment.

The process may include:

• An initial phone call or questionnaire
• A review of medical and genetic records
• Eye exams, imaging, vision tests, or blood tests
• A screening visit to confirm whether you meet the study's requirements
• A detailed informed-consent discussion
• Study visits before and after treatment
• Long-term follow-up to monitor safety and changes in vision

A trial may require more visits, tests, travel, and time than ordinary medical care. Some studies last a few months, while gene or cell therapy trials may follow participants for several years. Participation may provide access to an experimental treatment, but there is no guarantee of a direct benefit.

Researchers often need a comparison group to determine whether a treatment is truly responsible for any changes they observe.

Randomization means that participants are assigned to study groups by chance rather than choosing their group.

Depending on the trial, the comparison group may receive:

• Standard care
• A placebo (definition: An inactive treatment made to look like the real one, used in some trials so researchers can tell whether the actual treatment is responsible for any effect.), which looks like the study treatment but does not contain the active treatment
• A sham procedure (definition: A procedure that mimics the steps of a real treatment, such as an injection, without delivering the experimental therapy — used for comparison in some trials.) that copies parts of the treatment process without delivering the experimental therapy
• No study treatment during the comparison period

Not every clinical trial uses a placebo (definition: An inactive treatment made to look like the real one, used in some trials so researchers can tell whether the actual treatment is responsible for any effect.) or sham procedure (definition: A procedure that mimics the steps of a real treatment, such as an injection, without delivering the experimental therapy — used for comparison in some trials.). The study team must explain the design before you decide whether to participate.

Every trial has eligibility criteria, also called inclusion and exclusion criteria. These rules help protect participants and ensure that researchers can interpret the results accurately.

For an RP trial, eligibility may depend on:

• The gene involved
• The specific genetic variant (definition: A change in a gene's DNA sequence. A variant can be harmless, or it can disrupt how the gene works and cause disease.)
• Age
• The type and stage of the condition
• Current vision and the amount of functioning retina that remains
• Previous treatments
• Other medical or eye conditions
• Whether you can attend the required visits and follow-up appointments

Meeting a few basic criteria does not mean that you qualify. The study team must review your information and complete any required screening before confirming eligibility.

A trial's status tells you where it is in the enrollment process.

• Not yet recruiting: The study plans to enroll participants but has not started.
• Recruiting: The study is currently looking for participants.
• Enrolling by invitation: The study is enrolling only people selected by the researchers.
• Active, not recruiting: The study is continuing, but it is no longer accepting new participants.
• Completed: The study has ended normally. Results may not be available yet.
• Suspended: Enrollment or study activity has been temporarily stopped.
• Terminated: The study ended earlier than planned after enrolling at least one participant.
• Withdrawn: The study ended before any participants were enrolled.
• Unknown: The study's current status has not been confirmed recently. Do not assume that it is still open.

Preclinical research is not a clinical-trial status. It refers to work conducted in laboratories or animals before a treatment is ready to be studied in people.

Before you join a trial, the study team must explain what the research involves. This process is called informed consent.

You should receive information about:

• The purpose of the study
• What will happen during participation
• Known and possible risks
• Possible benefits
• Other treatment or care options
• The study's length and required visits
• How your information and samples may be used
• Costs, payments, and possible travel support
• Who to contact with questions or concerns

Signing an informed-consent form is not a contract. Participation is voluntary, and you may choose not to join or decide to stop later. Informed consent (definition: The process of a study team explaining a trial's purpose, risks, and requirements so a participant can decide, with full understanding, whether to take part.) is an ongoing process, so the study team should tell you about important new information that could affect your decision to continue.

Clinical trials must follow rules intended to protect participants and produce trustworthy results.

In the United States, most trials are reviewed by an Institutional Review Board, or IRB (definition: An independent group (often abbreviated IRB) that reviews a clinical trial's design and protections for participants before and during the study.). An IRB is an independent group that reviews the study's purpose, design, risks, consent process, and protections for participants.

Study teams must monitor participants for safety, document problems, protect private information, and report certain findings to oversight bodies. These protections reduce risk, but they cannot make an experimental treatment risk-free.

Before deciding, ask the study team:

• What is the study trying to find out?
• What phase is the trial?
• What is already known about the treatment?
• What risks or side effects have been reported?
• Will everyone receive the experimental treatment?
• How are participants assigned to groups?
• What exams, procedures, and follow-up visits are required?
• How much travel and time will participation require?
• Which costs are covered, and is travel support available?
• Who will provide medical care if a problem occurs?
• What happens if I decide to leave the study?
• Will I be told the study's results?
• Will I be able to receive the treatment after the trial ends?

It can help to bring a family member, caregiver, or trusted friend to the conversation and discuss the study with your own eye doctor or genetic counselor.

A study listed on ClinicalTrials.gov has not necessarily shown that its treatment is safe or effective. Some trials are testing a treatment in people for the first time, and some treatments do not succeed.

Before making a decision, review the study with a qualified eye specialist or genetic counselor and speak directly with the study team.