Why this study matters

Choroideremia is an inherited retinal disease in which degeneration progressively affects the retina and the supporting tissues needed for vision. For people living with choroideremia and their families, an important question is how quickly the central retina—the macula—changes over time. Answering that question is essential not only for understanding the disease’s natural history, but also for designing clinical trials that can reliably detect whether a potential treatment is making a difference.

A 2026 analysis from the multicenter NIGHT natural-history study examined changes in preserved autofluorescence (PAF) over a 12-month period. On fundus autofluorescence (FAF) imaging, PAF marks areas of the macula where autofluorescence remains detectable. Measuring the size and shape of these remaining regions can provide a structural view of retinal tissue loss in choroideremia.

The researchers found that macular PAF declined significantly in only one year. They also identified two baseline features—PAF area and PAF perimeter—that were associated with faster subsequent loss.

Measuring what remains in the macula

The study included 106 people with genetically confirmed choroideremia, contributing 163 eyes with gradable FAF images at both the first study visit and month 12. Researchers manually outlined PAF regions on the images, then used an automated ImageJ-based workflow to calculate two measurements:

  • PAF area: the total amount of preserved autofluorescent tissue in the macula.
  • PAF perimeter: the total boundary length around the preserved regions.

PAF regions can vary greatly between eyes and individuals. Some may be larger, while others may be fragmented into multiple separate areas. The investigators also assessed whether the fovea—the small central retinal region responsible for sharpest vision—was preserved, and whether PAF appeared as one region or multiple focal regions.

This approach allowed the team to look beyond a single snapshot and ask which baseline patterns were linked to structural change over the next year.

Key findings: measurable loss over 12 months

Across the study population, mean macular PAF area fell from 3.77 mm² at baseline to 3.37 mm² at month 12. This represented an average loss of 0.41 mm² over one year, a statistically significant change.

PAF perimeter also declined significantly, by an average of 1.04 mm. In practical terms, both the total preserved area and the boundaries of that area became smaller over the 12-month period.

The most notable result was that eyes with more PAF at baseline tended to lose more PAF during follow-up. A larger initial PAF area was independently associated with greater PAF loss. Likewise, a greater baseline perimeter was associated with greater subsequent loss.

This may reflect the fact that eyes with larger preserved regions have more remaining tissue at the edge of degeneration that can be lost over time. Perimeter may be especially informative because it captures the amount of border between preserved and affected tissue. A more extensive border could represent a larger area where degeneration is actively advancing.

In contrast, two features were not significantly associated with the amount of PAF loss over 12 months:

  • Whether the fovea was preserved at baseline
  • Whether PAF was present as one region or multiple focal regions

These findings suggest that, at least during this short follow-up period, the size and boundary characteristics of preserved macular tissue may be more informative for structural progression than foveal status or the number of separate PAF regions.

Implications for clinical trials and treatment development

The study supports macular PAF area measured with FAF imaging as a potential short-term structural endpoint in choroideremia research. An endpoint is a measurement used to evaluate change in a study. For clinical trials, useful endpoints need to change enough over the study period to be measurable and need to reflect meaningful disease-related biology.

Demonstrating significant PAF loss over 12 months is important because many inherited retinal diseases progress gradually. If an imaging-based measure can capture change within a year, it may help researchers evaluate investigational treatments more efficiently.

The association with baseline area and perimeter also has practical relevance for trial design. Studies may need to account for the amount and configuration of remaining PAF when enrolling participants or interpreting results. If people with larger preserved areas tend to show faster short-term loss, baseline structure could influence the expected rate of change in an untreated comparison group.

For treatment development, these results do not identify a therapy or show that an intervention slows disease. Instead, they help establish the measurements needed to test future approaches rigorously. A treatment intended to preserve retinal tissue could potentially be assessed by whether it reduces the rate of PAF-area decline compared with the decline expected from natural-history data.

Looking ahead

This NIGHT study analysis adds detailed evidence that structural macular loss in choroideremia can be detected over a relatively short timeframe. It also shows that the starting amount and perimeter of preserved autofluorescence matter when considering subsequent progression.

As researchers continue to develop and evaluate therapies for choroideremia, well-characterized natural-history data will remain central. Combining longitudinal imaging measures such as PAF area with carefully designed clinical trials may help clarify which approaches can preserve macular tissue and, ultimately, support vision for longer.