CLUSTER ANALYSIS FOR FUNCTIONAL CLASSIFICATION OF INTRAOCULAR LENSES BASED ON VISUAL ACUITY DEFOCUS CURVES

Intraocular Lenses (IOLs) have historically been classified as multifocal (MIOL), either bifocal or trifocal, extended depth of focus (EDoF), monofocal with enhanced depth of focus (Mono-EDoF), and monofocal. The growth of IOLs in the market has led to knowledge gaps about what of these historical classifications based on technical concepts can enclose new IOL models, sometimes being difficult to classify a new IOL in one of these categories. The aim of this study was to categorize intraocular lenses (IOLs) according to their functional attributes by primarily focusing on monocular distance corrected visual acuity defocus curves (VADC).

Scoping Review and Cluster Analysis

A systematic search of 436 clinical studies was performed on PubMed. Studies chosen for analysis were those published in English after 2010, involving patients who had undergone uneventful cataract surgeries or refractive lens exchange. Exclusion criteria were studies with patients with ocular comorbidities, a history of corneal laser refractive surgery, postoperative complications as the primary study focus, eyes requiring toric IOL implantation or additional corneal incisions (corneal astigmatism > 1.5 D), combined different targets (micro-monovision), or different IOL models (mix-and-match) between eyes. Two impartial reviewers scrutinized the search results for eligibility of 69 studies that comprised monocular VADCs and extracted data. Cluster analysis was applied to assess two main end-points: the Range of the depth of Field (RoF) and the increment in visual acuity from intermediate to near distances (ΔVA).

The retrieved VADCs involved a total of 2523 subjects and 3298 eyes implanted with 32 different IOL models. Two primary classifications emerged by the cluster analysis based on the achieved RoF at 0.2 and 0.3 logMAR levels: Full Range of Field (FRoF) and Partial Range of Field (PRoF) IOLs. For FRoF, three subcategories were distinguished by the cluster analysis based on ΔVA: Continuous (FRoF-C), Smooth (FRoF-Sm), and Steep (FRoF-St). Conversely, PRoF IOLs showed a consistent decline in visual acuity and were divided into two subgroups based on the RoF achieved: Narrowed (PRoF-N) and Extended (PRoF-Ex). An extra subcategory, Enhanced (PRoF-En), was established for 7 studies that fluctuated between PRoF-N and PRoF-Ex, depending on whether 0.2 or 0.3 logMAR was employed as the cut-off for RoF calculations.

Based on RoF and the shape of monocular VADCs, six distinct functional types of IOLs can be statistically identified by cluster analysis. Particularly PRoF-En, generally knows as enhanced monofocals, cannot be classified only by the RoF at 0.2 logMAR as it is usually described by international standards, requiring also of the RoF at 0.3 logMAR. This classification allows the surgeon to identify IOLs according to the visual acuity achieved along the range of the depth of field instead of technical concepts.