Pearls on choosing presbyopia correction IOLs

With increasing systemic and environmental risk factors for presenile cataracts, there has been a progressive decrease in the age of presentation of visually significant cataracts.[1] Consequently, there has been a quantum jump in cataract surgeries worldwide, and the demand for satisfaction of patients has also increased. The younger generation is active in traveling and even daring sports activities. Therefore, they require sharp and bright image not only when viewing billboards and watching movies, but also while cooking and working on computers. This has led us to look deep into optics and opportunities for managing presbyopia with intraocular lenses (IOLs). The presbyopic correction IOLs mainly include three categories: extended depth of focus (EDOF) lenses, multifocal lenses (MIOLs), and accommodating IOLs.

For all these IOLs, it is essential to realize the need for the assessment of ocular surface and treatment of any abnormality before surgery, measurement of precise preoperative biometry including total corneal astigmatism, application of appropriate newer-generation IOL formulas, ruling out any posterior segment pathologies, and last but not the least, uneventful surgery to yield desired results.

EDOF IOLs, which are distant dominant lenses, have far focus, which extends longitudinally to the intermediate distance with a plateau of the corresponding defocus curve.[2,3] There are several types of designs of these IOLs, ranging from pure EDOF based on spherical aberrations to hybrid multifocal–EDOF with refractive and/or diffractive optics.[4] The typical EDOF IOLs are based on nondiffractive optics with a higher potential for dysphotic phenomena because of their central structure, compared to pure EDOF IOLs, also referred to as enhanced monofocal IOLs (an extended intermediate range), and may have to depend on pupil constriction for intermediate acuity.[5] On comparison in vivo, both these IOLs have produced excellent and similar visual and refractive outcomes.[6] The American Academy of Ophthalmology has published a consensus statement as well as recommendations on evaluation of the performance of these lenses.[7] Several studies have demonstrated that these lenses provide excellent intermediate vision (especially ranging from 67 cm to 1 m) and better optical quality compared to MIOLs.[8,9,10]

The bilateral implantation of EDOF lenses has led to the possibility of decent near vision with micro-monovision. The use of emmetropia for dominant eye and residual myopia ranging from 0.5 to 1 D has shown good tolerance of anisometropia with statistically better near vision compared to eyes with a postoperative target of emmetropia in both eyes.[11,12,13] We have seen that almost 40% of our patients implanted with bilateral EDOF lenses with a targeted myopia of 0.5–1 D in the nondominant eye had a postoperative binocular visual acuity of 6/6 on Snellen’s visual acuity with a binocular near vision of N6. We have hypothesized that there may be a component of pseudo-accommodation along with micro-monovision for this postoperative outcome. The use of micro-monovision with EDOF lenses does not lead to complete spectacle independence at all distances, and this needs to be highlighted during preoperative counseling to prevent postoperative frustration and improve patient satisfaction.

MIOLs split light into different focal points. In refractive MIOLs, the optical zone is partitioned into areas with different refractive powers, while in diffractive MIOLs, alteration of the step width and the ring width of the ring helps in their multifocality. However, the neuroadaptation required to process these different images takes significant time and patience. Traditional bifocal refractive MIOLs have slowly evolved, owing to better understanding and exploiting of optical principles, to trifocal and panfocal diffractive IOLs. The proportion of light energy allocated to different foci is different with various designs of trifocal IOLs and contributes to the visual acuity at that focus. Our experience agrees with literature that new-generation trifocals have proven effective in giving intermediate and near vision to the patient without compromising the uncorrected distance acuity, thereby providing spectacle independence to the patient. However, this comes at a cost of reduction in optical quality, which manifests as glare and haloes, and a reduction in contrast sensitivity.[10,14] The newer-generation trifocals have been based on sinusoidal functions and have smooth optical surface without any sharp edges. Initial studies on their outcomes show promise.[15] This may help fuel research to make better IOL designs and innovation using newer optical properties.

A corneal astigmatism over 0.5 D can lead to a compromised visual performance, with maximum decline in depth of focus in multifocal lenses.[16,17] In terms of structure, plate loop haptics provide more rotational stability compared to C-loop haptics. Since most of the MIOLs have anterior diffractive elements, the toricity is usually incorporated on the posterior surface. The use of toric EDOF and toric multifocal lenses has shown effective postoperative visual and refractive outcomes when placed in the correct orientation, with good rotational stability, improving patient satisfaction and enabling spectacle independence.[18,19]

There have been multiple studies over the years that have compared the visual acuities in photopic, scotopic, and mesopic light conditions, the defocus curves, and patient satisfaction including spectacle independence among the two broad categories of EDOF lenses and MIOLs, with many having implemented the “mix-and-match” approach (EDOF IOL in one eye and multifocal in another) to prevent any biases.[20] In a recently concluded meta-analysis, the contrast sensitivity was better, especially at lower spatial frequencies, and the haloes were lesser in EDOF lenses compared to all other multifocal lenses, which highlights the advantage of EDOFs over multifocal lenses, especially for distance and intermediate visual acuities.[10] However, the decentration and tilt of IOL have more distinct effects on EDOF lenses compared to MIOLs (refractive more than diffractive in subgroup analysis).[21] Spectacle independence was similar for intermediate distances between both the groups. As expected, the trifocal IOLs fared better in freedom from spectacles at near distances (>92%) compared to EDOF lenses (70%).[9,22] There are lenses that bring the best of both worlds, that is, they have the combined the advantages of both these IOLs: hybrid multifocal–EDOF IOLs, which have also been shown to provide good continuous range of vision for the entire range of near to far distance, even in low-lighting conditions.[23]

Although the photic phenomena happen at a higher frequency in cataract surgery cases after corneal refractive surgery as anticipated, the implantation of presbyopia-correcting IOLs has shown a predictable response after corneal ablative procedures with improvement in all visual acuities and good postoperative satisfaction.[24,25]

An ideal IOL should be able to accommodate like a crystalline lens and help the patient see like a pre-presbyopic individual at various distances. Thus, the accommodating IOLs have been tried and tested. Most of these IOLs have a single optic and use the optic-shift principle. It was proposed that this could either be done using vitreous pressure or circumferential compression of haptics during ciliary body contraction that would vault the optic anteriorly. There have also been attempts to rely on fluid polymers inside the IOL and the elastomeric hinge of haptic to cause IOL movements, but the success has been quite limited.[26,27] However, this will not stop our quest in the development of an ideal accommodating IOL that will be the game changer in terms of presbyopia correction.

With such a wide range of options to choose from, preoperative counseling and understanding patients’ needs and demands are prerequisites to match them to the postoperative outcomes.

About the author

Prof Sudarshan Kumar Khokhar, MBBS (AIIMS), MD (AIIMS), FRCS (Edin). is currently working as Professor and Head of unit at Rajendra Prasad Centre, All India Institute of Medical Sciences New Delhi, India

Prof Khokhar is an expert in cataract and refractive surgeries like ICL, SMILE and LASIK. He has special interest in Myopia

Prof Khokhar over last 2 decades has been conducting instruction course on cataract and refractive surgery including pediatric cataracts at different national and international conferences like AAO, ESCRS, APAO, WOC, AAPOS etc,

Prof Sudarshan Khokhar has authored over 90 indexed publications in peer-reviewed journals and has six chapters in Textbook including a text book on Art of refractive surgery

He has authored pediatrics cataract ATLAS one of its kind

Prof Khokhar also authored pediatrics cataract surgery book with 54 videos for learning for residents

Prof Khokhar has devised and designed a cannula used for capsular painting in white cataracts which goes by his name “Khokhar’s capsular painting cannula” Prof Khokhar is the pioneer in using Plasma blade in PFV eyes

He was invited for live demonstration of his techniques in pediatric cataract at Westmead Children’s hospital Sydney

He was honored by Achievement awards by international bodies like APAO (2016) and AAO(2017),2018 (Siva Reddy oration award)

Prof Khokhar has more than 40 years of clinical teaching and Research experience at AIIMS New Delhi