Multi-luminance shape discrimination test shows reliability in low-vision RP population

A newly published observational study suggests that the Multi-luminance Shape Discrimination Test (MLSDT) may offer a reliable and clinically meaningful way to assess functional vision in patients with advanced retinitis pigmentosa (RP), a population in whom conventional visual acuity testing often fails to capture real-world visual performance.¹

The findings, published in Documenta Ophthalmologica, come as interest grows in alternative endpoints for inherited retinal diseases, particularly in the context of emerging therapies targeting patients with profound photoreceptor loss. In such populations, best-corrected visual acuity (BCVA) alone may inadequately reflect treatment benefit, prompting investigation into performance-based and patient-centered outcome measures.²

Study Design and Key Findings

The prospective observational study enrolled 35 participants, including 25 individuals with severe vision loss due to RP (defined as visual acuity ≥1.6 LogMAR) and 10 participants with normal vision.¹ The MLSDT evaluates functional vision by requiring participants to identify and grasp objects of varying shapes under different luminance conditions, generating quantifiable performance scores.

Test–retest reliability for the MLSDT exceeded 0.50, meeting commonly accepted thresholds for moderate reliability in early-stage validation studies.¹ Investigators also reported strong correlations between MLSDT performance and standard visual acuity measures, with correlation coefficients greater than −0.7.¹ A clinically interpretable relationship was observed: a 0.3 LogMAR difference in visual acuity corresponded to an approximately 2-level difference in MLSDT score.¹

In addition, MLSDT scores demonstrated moderate to strong correlations with visual field measures and patient-reported outcomes, supporting convergent validity.¹ Performance improved with higher luminance levels, underscoring the test’s ability to capture functional vision changes under varying environmental conditions.¹

Clinical Context: Limitations of Traditional Endpoints

Retinitis pigmentosa comprises a heterogeneous group of inherited retinal degenerations characterized by progressive photoreceptor loss, leading to nyctalopia, visual field constriction, and eventual central vision impairment.³ While BCVA remains a regulatory standard endpoint, it may remain relatively preserved until late disease stages and does not fully reflect mobility, object recognition, or daily visual function.²

This limitation has become increasingly relevant as investigational therapies—including gene therapies and optogenetic approaches—target patients with advanced disease, where traditional endpoints may lack sensitivity.⁴ Regulatory agencies, including the US Food and Drug Administration (FDA), have signaled openness to alternative functional endpoints in such contexts, provided they demonstrate validity and clinical relevance.⁵

Relevance to Emerging Therapies

The MLSDT has also been incorporated as a secondary endpoint in the phase 2b/3 RESTORE trial evaluating MCO-010, an investigational optogenetic therapy designed to confer light sensitivity to bipolar retinal cells. Although detailed peer-reviewed results from that trial remain limited, the sponsor has reported improvements of at least two luminance levels in MLSDT performance among treated patients at 52 weeks.

Optogenetic therapies represent a novel, mutation-agnostic approach that aims to bypass degenerated photoreceptors by targeting downstream retinal circuitry.⁴ Unlike gene replacement therapies, these approaches may not require genetic testing and could have broader applicability across inherited retinal diseases. However, demonstrating clinically meaningful benefit remains a key challenge, particularly in advanced disease populations.

Interpretation and Limitations

The current study provides preliminary evidence supporting the reliability and validity of MLSDT as a functional vision endpoint. However, several limitations warrant consideration. The sample size was small (n=35), and the study design was observational, limiting generalizability and precluding assessment of responsiveness to treatment over time.¹

Additionally, while correlations with established measures are encouraging, further validation in larger, multicenter cohorts is needed. Standardization, reproducibility across clinical settings, and sensitivity to longitudinal change will be critical for regulatory acceptance.

Independent replication and peer-reviewed data from interventional trials incorporating MLSDT will also be important to confirm its utility as a clinically meaningful endpoint. At present, published data supporting its use in registrational trials remain limited.

Broader Implications

The development of functional endpoints such as MLSDT reflects a broader shift in ophthalmology toward measuring outcomes that better align with patient experience. Similar efforts have been seen with mobility-based assessments and patient-reported outcome instruments in inherited retinal diseases.²

If validated in larger studies, MLSDT could complement existing endpoints by capturing aspects of vision that are directly relevant to daily functioning, particularly in patients with severe impairment.

References

1. Nanoscope Therapeutics. Validation of the Multi-luminance Shape Discrimination Test (MLSDT) in severe vision loss. Documenta Ophthalmologica. Published online 2026. https://link.springer.com/journal/10633

2. Massof RW. A systems model for low vision rehabilitation. Optom Vis Sci. 1995;72(10):725-736. https://journals.lww.com/optvissci/Abstract/1995/10000/A_Systems_Model_for_Low_Vision_Rehabilitation.5.aspx

3. Hartong DT, Berson EL, Dryja TP. Retinitis pigmentosa. Lancet. 2006;368(9549):1795-1809. https://doi.org/10.1016/S0140-6736(06)69740-7

4. Sahel JA, Boulanger-Scemama E, Pagot C, et al. Partial recovery of visual function in a blind patient after optogenetic therapy. Nat Med. 2021;27(7):1223-1229. https://www.nature.com/articles/s41591-021-01351-4

5. US Food and Drug Administration. Rare diseases: common issues in drug development guidance for industry. 2019. https://www.fda.gov/media/119757/download