Commentary: Macular hole area index - Is it a research index or clinical index?

Macular hole (MH) was an untreatable disease till 1991, when Kelly and Wendel suggested the role of pars plana vitrectomy (PPV) to achieve MH closure.[1] This was on the basis of the pathogenesis of MH as proposed by Gass et al.[2] However, they could achieve only 58% success in closing MH with PPV and gas tamponade alone. Eckardt et al. and Park et al. later in the year 1997 and 1999, respectively, introduced the concept of internal limiting membrane (ILM) peeling in addition to PPV and gas tamponade to achieve better closure rates.[34] They achieved >90% success in closing MH. After the addition of optical coherence tomography (OCT) to the armamentarium, the entire perspective of looking at MH has changed. The modern-day classification of MH is on the basis of OCT. The international vitreomacular traction study group classified MH as small, medium, and large on the basis of aperture size (minimum hole diameter).[5] It is well proven that MH size is the most important prognostic factor that determines the success rate in MH closure. Michalewska et al. introduced the concept of inverted flap surgery for large MH (aperture size >400 μm).[6] Since then, various modifications and newer techniques have been proposed for large MH. In the Manchester large macular hole study with conventional ILM peeling, the success rate was >90% till 650 μm aperture size.[7] Beyond that, the success rate decreased significantly to 76%. It is time that we revise the definition of a large MH and accordingly, the criterion for performing inverted flap MH surgery. Various MH indices were proposed in the past like macular hole index (hole height/base diameter), diameter hole index (minimum diameter/base diameter), and tractional hole index (maximum hole height/minimum diameter). However, none of these are popular among clinicians as the predictive value has not been widely reproducible. The minimum diameter and base diameter are the most important and independent prognostic factors that determine the success rate.[8] It is interesting that Venkatesh et al. have come up with newer indices on the basis of area rather than linear metrics.[9] They have processed the scans in Image J software and analyzed the correlation between various newly proposed indices and success rate and found out that MH area index (MAI) predicts outcomes better than the rest. However, the authors have not suggested any grading on the basis of MAI and also not performed or commented on inverted flap surgery. The mean minimum hole diameter in the series was 938.3 ± 398.9 μm. The authors have performed conventional MH surgery with a success rate of 59%.

Also, exporting the scans to Image J and processing it over there to obtain all these newer indices may not be user-friendly for many clinicians especially if they are not tech-savvy. In contrast, minimum hole diameter and base diameter are simple and very easy to measure by anyone using the calipers that are inbuilt in the OCT machine. Nevertheless, if MAI is proven to be at par or superior to aperture size in predicting the success rate, the OCT manufacturers might incorporate MAI in the OCT software itself. This may simplify the entire process. Similar to the Manchester study, we need to understand how this MAI can help us achieve better success rate. I hope the authors take this forward and come up with a classification system on the basis of MH area with calculated success rate in the future. And if that gets incorporated in most of the standard OCT machines, MAI will be value addition. Till then it will be research index rather than a clinical index.