Evidence-Based Functional Classification Of Intraocular Lenses

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 IOLs according to their functional outcomes by primarily focusing on monocular distance corrected visual acuity defocus curves (VADC).

Scoping Review and Cluster Analysis

436 clinical studies were retrieved from PubMed. Studies chosen for analysis were those published after 2010, involving patients who had undergone uneventful surgeries. Exclusion criteria were studies with patients with ocular comorbidities, history of laser refractive surgery, postoperative complications as the primary focus, corneal astigmatism > 1.5 D, combined different targets (micro-monovision), or different IOL models (mix-and-match) between eyes. Two 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 (ΔVA).

The retrieved VADCs involved a total of 2523 subjects and 3298 eyes implanted with 32 different IOL models. The cluster analysis resulted in 2 main categories for a cut-off of 2.3 D of RoF at the VA level of 0.2 logMAR (PARTIAL ≤ 2.3 D and FULL >2.3 D). Three subgroups were identified for PARTIAL-RoF IOLs: Narrowed (< 1.2 D), Enhanced (1.2 to 1.59 D) and Extended (1.6 to 2.3 D) at the VA level of 0.2 logMAR. On the other hand, for the FULL-RoF classification, the ΔVA led to three subgroups considering the cut-offs of 0.05 and 0.15 logMAR for ΔVA: Continuous (<0.05 logMAR), Smooth (0.05 to 0.15 logMAR) and Steep (> 0.15 logMAR). For the PARTIAL-RoF Enhanced IOLs, the RoF at the VA level of 0.3 logMAR should be also considered.

Based on RoF and the shape of monocular VADCs, 6 functional types of IOLs can be statistically identified by cluster analysis: Full Range of Field (FULL-RoF) and Partial Range of Field (PARTIAL-RoF) IOLs. For FULL-RoF, 3 subcategories were distinguished by the analysis based on ΔVA: FULL-RoF Continuous, FULL-RoF Smooth, and FULL-RoF Steep. Conversely, PARTIAL-RoF IOLs showed a monotonous decrease in visual acuity and were divided into two subgroups based on the RoF achieved: PARTIAL-RoF Narrowed and PARTIAL-RoF Extended. An extra subcategory, PARTIAL-RoF Enhanced, was established for 7 studies that fluctuated between Narrowed and Extended, depending on whether 0.2 or 0.3 logMAR was employed as the cut-off for RoF calculations.