Post-laser vision correction cataract surgery: What makes it challenging?

With an increase in the number of post-laser vision correction (LVC) patients seeking cataract surgery, IOL power calculation, targeting post-surgery emmetropia, and managing patient expectations have become more challenging than ever. This has become more intriguing with the current platform of intraocular lenses (IOLs) available for selection, moving from monofocal to premium IOLs ranging from torics, multifocals, extended depth of focus (EDOF), trifocal IOLs, and light-adjustable lenses (LALs). In India, understanding post-LVC cataracts is important, as, in contrast to the West, there exists a group of LVC patients who undergo refractive surgery in their early twenties or thirties and another group who undergo presbyopic LVC surgery. With both these groups being similar in their desire to be spectacle-independent, the demand for "lifestyle ophthalmic care" seems to have risen manifold. This places great stress on the surgeon's ability to comprehend the delicate interweave of post-LVC cataract surgery, premium IOLs, and corneal aberrations, along with optimally customizing the needs of the patients and their expectations. The resultant outcomes may not always be as desired.[1] Preoperative workup in post-LVC cataracts differs from routine evaluations as there needs to be a greater emphasis on topography and aberration analysis besides biometry evaluations. Corneal topography helps to assess the type and perfection of the refractive ablation performed, the residual astigmatism, and the ocular surface tear stability. The documentation and analysis of the post-LVC corneal aberration status with the help of corneal diagnostic imaging by either aberrometers or topography is important to choosing the right IOL type for these patients. Erroneous corneal refractive power measurements and effective lens position (ELP) estimation are common in eyes with post-LVC cataracts. Detailed corneal imaging including tangential curvature maps, epithelial remodeling patterns, and Gullstrand ratio, has been recommended to help enhance the prediction accuracy of IOL power in these cases.[2] Refractive surgery corrections commonly performed range from myopic or hyperopic flap-based or surface ablation treatments, enhancements, kerato-lenticule extractions, or non-laser procedures, such as radial keratotomy (RK). Achieving postoperative refractive outcome of target emmetropia within ±0.5 D has been reported to be lesser than 70% in cataract surgery in eyes with a previous laser refractive surgery as compared with cataract surgery in eyes with no previous corneal refractive surgery, in which over 80% of eyes have been noted to achieve target emmetropia within ±0.5 D.[3,4] Intraoperative aberrometry has enabled the use of premium IOLs in post-LVC cataract eyes, helping ophthalmic surgeons to be independent of previous clinical history details and newer IOL power calculation formulas. Intraoperative aberrometry provides for the refinement of IOL power and axis in these eyes, enabling better refractive accuracy. Cautious use of post-myopic laser in-situ keratomileusis (LASIK) formulas such as the Shammas formulas and intraoperative aberrometry is required depending on the nature of the refractive surgery the patient has undergone. The operating surgeon needs to be aware of the limitations of the applicable formulas in accordance with the refractive correction undergone and the inadequacies with intraoperative aberrometry in post-RK eyes. Intraoperative aberrometry has been observed to be comparable to Barrett formulas for post-myopic LVC cataract IOL power calculations and normal eyes, whereas Barrett True-K formula was noted to perform better in post-hyperopic LVC eyes.[5] Conventionally, many surgeons prefer to use the available online calculators or formulas such as Shammas and Haigis-L formula for post-LVC cataract IOL power calculations.[6] The Camellin–Calossi formula is a new introduction that has recently been compared with Shammas, Haigis-L, Barrett True-K No History, Masket, modified Masket, and Barrett True-K formulas and can be considered as a good option for IOL power calculation in eyes with previous myopic LVC cataracts.[7] A recent study comparing the traditional post-LVC formulas (Barret True-K no-history and Haigis-L) with reflectometry data, and ray tracing IOL calculation software (OKULIX; Panopsis GmbH, Mainz, Germany) with OCT data (Heidelberg Engineering Anterion) reported ray tracing calculation based on OCT data from the Anterion device to provide equivalent or better results than traditional post-LVC formulas.[8] A clear understanding of the role of asphericity, aberrations, and premium IOL implantation in post-LVC cataract surgery procedures is imperative to optimize refractive outcomes in accordance with patient expectations. Higher-order aberrations influence functional visual acuity, especially spherical aberration and coma. The virgin cornea has low amounts of positive spherical aberration, which the crystalline lens counters in the initial years of life. The changes in the higher-order aberration profile that occur with aging are not best assessed by the routinely used high-contrast Snellen distance acuity charts or the Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity testing charts. There is an increase in the positive spherical aberrations commonly related to the internal optical changes resulting from lenticular changes, whereas the increase in coma is attributed to age-related corneal changes. It is imperative to understand the change in the aberration profiles of the human cornea, which in its normal state has a positive spherical aberration. A post-myopic laser correction cornea tends to have a slightly greater positive spherical aberration, whereas post-hyperopic ablation corneas have a negative corneal spherical aberration. Lower-order aberrations are tackled well with the conventional IOL power calculations and toric measurements. Higher-order aberrations resulting from laser ablation treatments interfere with the quality of post-LVC cataract surgery vision, which can worsen significantly with an incorrect choice of IOL. The reduction in contrast sensitivity and disturbing postoperative glare and haloes can significantly worsen the quality of vision, demanding a more optimal "lifestyle ophthalmic care delivery" in such cases. Incorporation of aspheric design into a majority of available toric, multifocal, and accommodating IOLs is prevalent in recent times. Aspheric IOLs use has been proclaimed to help in the reduction of the preoperative normal corneal-positive spherical aberration and improve visual function and contrast sensitivity in mesopic conditions. Lenses with negative or zero spherical aberration have replaced positive spherical aberration IOLs with literature demonstrating that countering the positive spherical aberration of the cornea helps to improve visual outcomes, enabling better contrast sensitivity, especially under dim light.[9] However, a meta-analysis on this did not report clinically relevant differences in BCVA between aspheric and spherical IOL implantation.[9] Following myopic LVC, in which there is an increased positive spherical aberration, the choice of an IOL with the most negative spherical aberration is recommended. In eyes that have had hyperopic LVC, the choice of an IOL with positive spherical aberration or an aberration-free lens is recommended. In cases where the LVC has resulted in a misaligned or irregular ablation treatment profile, aberration-free IOL is recommended as it is less sensitive to optical decentration. Although toric IOLs are acceptable, it will be prudent to avoid multifocal and other premium IOLs in post-LVC eyes, which tend to decrease contrast sensitivity and glare acuity further. Low corrections by laser ablations between −4.0 and +1.5 D may be tolerant toward adapting to premium IOLs; however, our understanding needs to evolve further to help refine refractive and visual outcomes in these eyes. The recent innovation of light-adjustable intraocular lens (LAL) is best recommended for post-LVC cataract surgery, which permits customized modification in postoperative IOL power to refine the refractive surprise and enable better refractive outcome.[10] Tailoring a special postoperative workflow and comprehending the alterations in the optical characteristics of the LAL that result from the light adjustment is essential when employing LALs in post-LVC cataracts. LALs allow for postoperative adjustments for defocus and astigmatism. However, the contrasting outcomes shown in clinical studies in post-refractive cataract surgery cases highlight the need to scrutinize the effectiveness of LALs in these eyes. The postoperative adjustability afforded by LAL in a recent study[11] on 45 eyes with single refractive surgery and 31 eyes with two or more refractive surgeries noted 66% to be within ±0.25 D and 86% to be within ±0.50 D of target refraction. The refractive outcome in this study showed 74% of the post-LVC cataract eyes achieving 20/20 or better uncorrected distance visual acuity (UCDVA), 88% achieving 20/25 UCDVA or better, and 93% achieving 20/20 or better best-corrected VA postoperatively. Whatever the method resorted to in IOL power estimations in post-LVC cataract situations, it is prudent to comprehend the realistic expectations of the patient. It is imperative to strengthen patient counseling pertaining to limitations of IOL power calculation methods and currently available devices to appraise the patient on the possibility of addressing post-cataract surgery refractive surprise with subsequent procedures such as kerato-refractive enhancement, IOL exchange, or piggyback lens after the cataract procedure. One also needs to pay particular attention to the patient's visual needs, existing binocular refractive status, and personality, before finalizing a decision on accommodating IOLs or mini monovision in these eyes. Understanding how the advancements in IOL calculation formulae apply to LVC cataract eyes is important besides preparing for a refractive surprise that might mandate an IOL exchange, especially while handling higher-end demanding clientele and if using diffractive technology and not having access to the LAL. Explaining to the patients, the limitations of outcome in post-LVC cataract surgery, including the imperfection involved in achieving target refractive outcome, the heightened concern of reduction in contrast sensitivity that would persist from higher order aberrations and disabling glare and haloes, is imperative. Image simulation demonstration can also help to acquaint the patient with the postoperative vision expectation. It remains to be observed in coming times how technological advancements can help us to further refine our outcomes in post-LVC cataract surgery.