Everything you ever wanted to know about EDOF IOLs
Knowing what lenses are available for different patients is essential
Currently available presbyopia correcting IOLs can be classified as pseudoaccommodative IOLs – multifocal IOLs, segmented bifocal and trifocal IOLs including the AT LARA ® (Carl Zeiss Meditec), FineVision (PhysIOL, Belgium), PanOptix (Alcon); RayOne Trifocal (Rayner) and extended depth of focus (EDOF) IOLs; partially accommodative IOLs, such as Crystalens (Bausch + Lomb) and Synchrony dual optic IOL (Abbott Medical Optics) and accommodating IOLs such as FluidVision (PowerVision), Juvene (LensGen) etc. EDOF IOLs have become a popular choice because of better intermediate vision with less light scatter than monofocals, smaller haloes and glare than multifocals while working unlike accommodative IOLs.
Certain precautions are, however, still important while using EDOF IOLs, such as precise IOL power calculation; preoperative identification and if possible treatment of ocular comorbidities such as dry eye, epithelial basement membrane disease; surgical challenges such as pseudoexfoliation, subluxation, small pupil etc as well as conditions affecting postoperative outcome such as epiretinal membrane, diabetic macular oedema, age-related macular degeneration etc. However, EDOFs are preferred over multifocals in eyes with maculopathy, irregular corneas or glaucoma.
Proper patient counselling and understanding patient needs is important, as is setting realistic expectations, especially with regard to the possibility of needing reading glasses, as well as the occurrence of some glare and haloes.
While multifocal IOLs have two distinct foci with blurry vision in between, EDOF IOLs work by having one elongated focal area giving an extended depth of focus. As peak resolution is only minimally affected, reasonably clear vision is obtained at all distances (especially far and intermediate) with lesser side-effects of glare, haloes or loss of contrast as compared to multifocals. The AAO Task Force consensus statement requires EDOF IOLs to be within one line of BCVA of monofocal IOLs; to have 0.5D more of defocus than a monofocal at 20/30 level (approximately 1.25D defocus) and lastly, 50% of patients to be better than 20/30.
Although EDOF IOLs give good uncorrected distance and intermediate vision, near vision with a higher add multifocal is better. Therefore, bilateral EDOF with -0.5 to -0.75D micromonovision strategy or a mix-and-match strategy with EDOF in the dominant eye together with +3.25 near add multifocal in the non-dominant eye may be used if the patient desires more near vision.
EDOF IOLs work on different principles:
A) Echelette design: The Tecnis Symfony IOL (AMO, California) was FDA approved in 2016. It is a biconvex, anterior aspheric and posterior achromatic diffractive surface IOL with an echelette design and the ability to reduce chromatic aberration. Bilateral implantation with micromonovision has shown to give very satisfactory vision at all distances. The Symfony Toric IOL can also correct coexistent astigmatism. The AT LARA 829MP (Carl Zeiss Meditec) is another EDOF lens that, in pre-clinical studies, has shown higher visual acuity over a wider range of focus than Tecnis Symfony. A diffractive aspheric design, chromatic correction and smoother phase zones with shallower angles optimise contrast sensitivity and minimise light scattering and visual side-effects.
Postoperatively, patients can show over minus values on both autorefractor and manifest refraction. The highest plus possible should therefore be prescribed by using a fogging technique.
B) Small-aperture IOLs: The IC-8™ (AcuFocus) is a single-piece hydrophobic 6mm optic monofocal IOL utilising a pinhole principle (a non-diffractive 3.23mm diameter opaque PVDF mask with 1.36mm central aperture), similar to the Kamra corneal inlay, to increase depth of focus to about 3D. It is especially effective in post-LASIK eyes and corneas with irregular astigmatism. Results have shown good distance, intermediate and near vision, especially when targeting for -0.75D of myopia and it can improve up to -1.5D of astigmatism. It is also more forgiving of missing target refraction. Posterior fundus imaging is possible through the small aperture and vitreo-retinal surgery can be performed when required. The XtraFocus Pinhole implant (Morcher) designed by Trinidade et al. is a small-aperture sulcus IOL made of black acrylic with a central pinhole that extends depth of focus and can be used for high corneal irregular astigmatism such as post-RK patients.
C) Low-near add multifocal IOLs: These are now sometimes added under the EDOF group as they are directed mainly at improving distance and intermediate vision. This includes the Lentis Comfort (Oculentis), which has an asymmetric near sector and a near add of +1.5D translating to +1D at spectacle plane. Though the add power is lower, there is still a split of light into two or three foci, which results in some contrast sensitivity loss.
D) Combination/customised technologies: A combination of EDOF technology on accommodative lens optics can add to overall benefit and increase the range of vision further. The Swiss Advanced Vision (SAV-IOL) allows IOL customisation using a web-based configurator to obtain desired visual outcomes by offering differing light distribution ratios for near, intermediate and distance vision.
The Mini Well Ready IOL (SIFI Medtech), based on wavefront technology, has an aspheric profile with three circular zones – central distance, surrounding distance with spherical aberration of opposite sign and a peripheral distance with monofocal characteristics that together give a range of focus.
Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India and can be reached at email@example.com
Comment from Marie-José Tassignon:
Extended Depth of Focus, also called Extended Range of Vision, is another name for low-grade accommodative range IOLs. EDOF can be achieved by different optical principles, monocular or binocular e.g.: small-aperture corneal inlays, spherical aberrations, diffractive/ refractive IOLs, mix-and-match implantation of IOLs, monovision etc. EDOF IOLs propose an intermediate solution for the patient. While bifocal (and to a lesser degree trifocal IOLs) provided sharp vision at far and at near, patient’s intermediate vision was often poor. The new profile of EDOF IOLs proposes to compensate for this intermediate vision but will not give full correction at near. This compromise will most probably be more acceptable for a larger range of patients, namely those who prefer better image quality than getting rid of spectacles for 100% of their daily activities. It will be easier for the prudent ophthalmologist to propose an EDOF to their patients. Toric EDOFs will increase patient satisfaction, provided they are well centred. Centration remains the big issue – however, slight decentration will be better tolerated with EDOF IOLs.
Marie-José Tassignon MD, PhD, Professor Emeritus and Immediate Past Head, Department of Ophthalmology, Antwerp University, Antwerp, Belgium