Best corrected visual acuity (BCVA) has served as the cornerstone functional efficacy endpoint in ophthalmic clinical research for many decades.
Its dominance is reflected in guidance from both the US Food and Drug Administration (FDA),1 and the European Medicines Agency (EMA),2 where BCVA remains the primary endpoint for key indications such as neovascular age-related macular degeneration (nAMD),3 diabetic macular edema (DME),4 and other retinal diseases. The result is a vast legacy dataset—tens of thousands of patients across hundreds of trials—anchoring BCVA’s place in evidence generation.
Yet the limitations of a fovea-centric, high-contrast measure gain significance in an era where earlier disease detection and more nuanced, structure-function relationships are becoming increasingly important. As the field accelerates toward AI-enabled analytics, home-based testing, and biomarker integration, the central question becomes: How long will BCVA retain its status as the gold standard?
This article reviews why BCVA gained—and still holds—its central role; where it falls short; and how emerging objective and digital visual assessment tools, alongside traditional subjective measures, may reshape the future of clinical trials and patient care.
BCVA as the gold standard functional endpoint
One of the strongest arguments for BCVA’s continued use is its intuitive clinical meaning. Gains or losses in letters on an Early Treatment Diabetic Retinopathy Study (ETDRS) chart provide a direct, interpretable measure of foveal-centered function.5 For clinicians and regulators, BCVA changes are straightforward to communicate and relate well to common, real-world visual tasks.
BCVA is also highly sensitive to major functional changes, particularly in conditions where central vision is directly compromised. Anti-vascular endothelial growth factor (VEGF) therapies, for example, demonstrated dramatic, paradigm-shifting improvements in nAMD, with treatment benefits detected through high contrast, photopic BCVA gains, particularly in diseases where foveal involvement directly impacts BCVA sensitivity.6
In cataract surgery, BCVA reliably captures moderate to large improvements in optical clarity and in many posterior segment diseases,7 BCVA remains strongly correlated with therapeutic benefit.
Equally important is the depth of historical data supporting BCVA. Major registration trials over several decades have relied on this endpoint, creating a robust comparative framework. When sponsors design new studies, the ability to contextualize outcomes against extensive, well-characterized benchmarks remains invaluable for scientific interpretation and regulatory assessment.
Why BCVA remains reliable: The power of standardization
A major reason BCVA maintains regulatory favor is its standardized, reproducible testing environment.
The ETDRS protocol introduced strict controls around:8
- Testing distance
- Chart illumination
- Character size and spacing
- Chart design and contrast.
With 5 letters per line and 0.1-logMAR progression, ETDRS charts avoid the nonlinear steps inherent to Snellen charts.9 This linearity ensures each letter carries equal weight, reducing variability and increasing statistical power in clinical trials.10
Standardization extends beyond charts. Certified technicians apply:
- Uniform patient instructions
- Consistent refraction procedures
- Tightly controlled testing conditions
This disciplined protocol minimizes site-to-site variability, a critical factor in multicenter trials. Test-retest variability for ETDRS BCVA typically falls within 5 to 7 letters, whereas other visual acuity charts may vary by more than 10 letters without standardized lighting or scoring.
Strict BCVA training and certification programs, such as those developed by Lexitas, remain essential for maintaining data integrity and reproducibility. Reinforcing best practices—including consistent illumination control and accurate refraction—is central to ensuring reliable, regulatory-grade outcomes.
Recognized limitations of BCVA
Despite its strengths, BCVA’s limitations are increasingly evident as the field aims to detect disease earlier and assess more nuanced functional changes.
Four of the most documented limitations include:
- Poor sensitivity in early disease
- Ceiling effects
- Floor effects and low-end variability
- Weak correlation with real-world functioning
Poor sensitivity in early disease
In many chronic eye conditions, structural abnormalities precede functional decline detectable via high contrast, photopic BCVA:
- Early AMD: Drusen accumulation and subtle RPE changes may be evident on imaging while BCVA remains near normal.11
- Early glaucoma: As a fovea-centric measure, BCVA cannot detect early retinal ganglion cell loss.12
- Dry eye disease: Fluctuating vision, glare, and quality-of-vision symptoms are not reliably captured by high-contrast acuity testing.13
- Early DME: Retinal thickening and edema can be substantial before BCVA begins to decline.14
Because BCVA reflects only central, high-contrast recognition, it lacks sensitivity to contrast deficits, localized scotomas, distortion, or functional impairment under real-world lighting conditions.
Ceiling effects
Patients entering trials with good baseline vision have limited opportunity to show measurable improvement, potentially obscuring therapeutic benefit.15
High-performing patients may show minimal BCVA change despite meaningful improvements in:
- Contrast sensitivity
- Low-luminance visual acuity
- Night vision
- Reading performance
- Driving capability
- Overall quality of vision
Floor effects and low-end variability
At low visual acuities, variability increases due to fatigue, learning effects, attention shifts, and environmental fluctuations. Small shifts in lighting or patient motivation can produce large swings, reducing BCVA reliability in advanced disease.
Weak correlation with real-world functioning
High-contrast letter recognition does not replicate daily visual demands under conditions involving:
- Glare
- Motion
- Low contrast
- Dynamic lighting
- Crowding
A patient’s functional vision may diverge meaningfully from chart-based BCVA performance.
The future of visual assessment: beyond a single endpoint
As the field continues to innovate, several emerging tools and methodologies may complement—or eventually challenge—BCVA’s primacy.
AI-derived structural biomarkers
Advances in AI now allow extraction of subtle retinal biomarkers from OCT and other imaging modalities to estimate BCVA or predict future functional change.16,17,18
These algorithms may support endpoints for:
- Pediatric populations
- Individuals with low vision
- Patients with limited cooperation
- Situations where BCVA cannot be reliably obtained
AI-driven structural biomarkers, like ellipsoid zone attenuation in geographic atrophy, may also detect disease progression earlier than standard BCVA loss, enabling more proactive therapeutic intervention.19 This may result in validated structural endpoints becoming the preferred approach to avoid functional decreases.
VR, AR, and at-home mobile testing
Immersive and remote technologies are rapidly evolving:
- Virtual and augmented reality (VR/AR) platforms can simulate real-world environments, capturing contrast sensitivity, motion perception, depth cues, and glare performance.
- A pilot study found that a virtual reality adaptation of the Pelli-Robson contrast sensitivity test produced results comparable to in-office testing on a commercial VR headset.20
- A prospective comparison of VisuALL VR perimetry against Humphrey automated perimetry in 43 glaucomatous eyes found strong parity in mild and moderate disease, though parity declined in severe visual field loss.21
- A study comparing three augmented reality devices (Ziru, IrisVision, NuEyes-Pro3) in patients with low vision found that two of the three produced significant improvements in distance and near visual acuity and contrast sensitivity.22
- Smartphone-based visual testing continues to improve precision, allowing longitudinal monitoring outside the clinic and supporting retention in long-term trials.
- The K-VA smartphone application was validated against the ETDRS chart in 171 patients with various ocular diseases, supporting its use for VA testing without requiring in-person clinic visits.23
- A smartphone-based visual acuity application demonstrated clinical-grade agreement with best corrected visual acuity measurements, reinforcing feasibility for remote, self-administered testing.24
As validation increases, these tools may supplement traditional clinic-based measurements with ecologically valid data.
Integrative, holistic endpoints
Future trial designs may rely on composite functional endpoints incorporating:
- BCVA
- OCT structural biomarkers
- Contrast sensitivity
- Reading speed
- Microperimetry
- Mobility testing
- Patient-reported outcomes (PROs)
Such multidimensional assessments could offer a more comprehensive view of visual function and its impact on quality of life.
Regulatory considerations
FDA typically considers a 15-letter (3-line) ETDRS change to be clinically meaningful in drug development. While agencies encourage innovation in endpoint design, sponsors bear the responsibility of validating these endpoints and demonstrating their relationship to meaningful functional outcomes.
Until regulatory frameworks evolve further, BCVA will remain central—though increasingly supplemented by multimodal structural and functional measures.
Conclusion
BCVA has earned its place as the gold-standard functional endpoint through decades of consistent use, intuitive interpretability, and rigorous standardization. But its limitations—particularly in early disease detection and real-world functional relevance—are accelerating the field toward more comprehensive and technologically advanced assessment strategies.
As AI-enabled analytics, high-resolution imaging, VR/AR platforms, and integrative endpoints continue to mature, ophthalmology may transition from a single dominant functional measure to a multidimensional, patient-centered assessment paradigm.
For the foreseeable future, BCVA will likely remain a key reference point, but not the whole story.
