Byline:
Based on research by Andrii Ruban et al., published in the Asia-Pacific Journal of Ophthalmology (2025)
🧠 Why Surgeons Needed a New Metric
For decades, the Minimum Linear Diameter (MLD) has been the go-to OCT measurement for classifying idiopathic full-thickness macular holes (iFTMH) and predicting surgical outcomes. But MLD has a blind spot: it measures the narrowest point of the hole, not the true tissue gap that must be bridged for closure.
This means two holes with the same MLD can require vastly different surgical efforts—and yield different outcomes. The new study introduces the Foveal Actual Defect (FAD) as a more functionally relevant biomarker.
📐 How FAD Is Calculated
FAD is measured on a horizontal OCT B-scan through the fovea, using the External Limiting Membrane (ELM) as a reference.
Formula:
FAD = Basal Diameter (BD) – (Detached Nasal Retina Length + Detached Temporal Retina Length)
By subtracting the lengths of the detached retina from the basal diameter, FAD captures the actual neurosensory tissue gap—the distance that must be closed for primary healing.
📊 Study Design and Results
- Sample: 57 eyes from 53 patients with iFTMH
- Procedure: 25G pars plana vitrectomy (PPV), ILM peeling, SF₆ gas tamponade
- Tailored Techniques: Surgical method chosen based on FAD size
- Follow-up: Mean 35 weeks
Key Outcomes:
- Primary closure rate: 94.7%
- Final closure rate: 100%
- Day 1 closure: 89.5% (linked to better functional recovery)
- BCVA improvement: From 0.8 logMAR pre-op to 0.1 logMAR at 6 months
- Predictive power: FAD correlated more strongly with 6-month BCVA (ρ = 0.37) than MLD (ρ = 0.34) or BD (ρ = 0.23)
🛠️ The FAD-Based Decision Support System (DSS)
The authors propose a new classification and surgical roadmap:
| FAD Size | Classification | Surgical Goal | Recommended Technique |
|---|---|---|---|
| ≤ 200 µm | Small | Minimal displacement | ILM peeling ± subretinal fluid drainage |
| 200–400 µm | Medium | Moderate displacement | ILM peeling + drainage + edge apposition |
| > 400 µm | Large | Maximum displacement | Hydrodissection or subretinal BSS injection + centripetal displacement |
📚 Case Studies: Same MLD, Different FAD
Four patients with similar MLDs (~420–460 µm) had very different FADs—and required different surgical approaches:
| Case | MLD (µm) | FAD (µm) | Technique | Closure Timing | BCVA Outcome |
|---|---|---|---|---|---|
| #1 | 412 | 144 | ILM peeling + drainage | Day 1 | 0.9 |
| #2 | 419 | 275 | ILM peeling + drainage + edge apposition | Day 2 | 1.0 |
| #3 | 426 | 338 | ILM peeling + drainage + edge apposition | Day 1 | 0.7 |
| #4 | 459 | 422 | ILM peeling + hydrodissection + drainage + edge apposition | Day 1 | 0.9 |
Takeaway: MLD alone would have classified all as “large” holes, but FAD revealed the true complexity and guided more effective, individualized surgery.
💡 Why Day 1 Closure Matters
The study emphasizes that primary intention healing—closure on the first postoperative day—yields the best anatomical and functional results. If the intraoperative retinal displacement meets or exceeds the FAD, closure is likely immediate. Delayed closure often involves glial tissue filling (“secondary intention”), which correlates with poorer visual outcomes.
⚠️ Limitations and Future Directions
- Manual measurement: Subjective and grader-dependent
- Automation potential: AI integration into OCT could standardize FAD measurement and even calculate defect surface area
- Additional biomarkers: Combining FAD with photoreceptor integrity and MH height could further refine prognosis
🧠 Conclusion
The Foveal Actual Defect is more than just a new number—it’s a paradigm shift. By quantifying the true retinal gap, it enables surgeons to choose the right technique for the right patient, improving closure rates and visual recovery.
The authors believe FAD should join the core set of OCT biomarkers for iFTMH, forming the backbone of a personalized surgical strategy.
Reference:
Ruban A, Prudyus V, Zolnikova A, et al. Foveal actual defect (FAD): A novel OCT biomarker for prognosis and surgical decision support in idiopathic full-thickness macular hole. Asia-Pacific Journal of Ophthalmology. 2025. Read the full study here.
