Choosing the Right Lens
Every patient aspires to be able to see crystal clear at all distances and it is therefore imperative to set realistic expectations. Choosing an IOL is a combined decision involving both surgeon and patient...
Every patient aspires to be able to see crystal clear at all distances and it is therefore imperative to set realistic expectations. Choosing an IOL is a combined decision involving both surgeon and patient. Factors needing consideration include visual requirements of the patient, preference for distance dominated, intermediate or near dominated work, previous prescription, spectacle or contact lens wearing habits and satisfaction with the same, actual reading distance, ocular dominance, anatomy of the eye, refractive state including higher order aberrations (HOA). Ocular and systemic co-morbidities, personality and spending ability of the patient, and options for insurance coverage/co-payment also must be considered. Dr. Soosan Jacob, MS, FRCS, DNB reports
CHOOSING IOL TYPE:
Pre-operative assessment of visual needs:
Once cataract surgery is decided on, it is important to have a discussion with the patient. The Dell questionnaire developed by Steven Dell has many advantages: it easily and rapidly facilitates dialogue with the patient, establishes common vocabulary, helps explain that optical compromises are often required, and sets patient’s expectations. It also reduces pre-and post-operative chair time and helps avoid dissatisfied patients. Pre-operative contact lens trials, images showing expected photic phenomena and contrast levels, and simulations such as SimVis (2EyesVision) can also help the patient understand what might be expected after surgery.
Monofocal IOLs may be used in patients who do not mind wearing spectacles. Monovision and micromonovision are useful strategies adopted with monofocals to attain reasonable freedom from glasses for many activities. Good distance visual acuity in dominant eye and either intermediate or near vision in non-dominant eye can be aimed for depending on the patient’s requirements.
Monofocals are also useful in patients with ocular comorbidities such as macular pathology or glaucoma where they provide good optical quality without photic phenomena or loss of light/contrast sensitivity. They have also been used successfully in middle to lower income economies for high volume camp based surgeries as they provide an inexpensive means to get good visual quality, albeit relying on spectacles for an uninterrupted range of vision.
Monofocal aspheric IOLs are helpful in various situations. Negative spherical aberration IOLs may be used in patients with large pupils, nighttime driving needs, or post-myopic LASIK. Corneal positive aberrations are neutralized completely by Tecnis®, AMO (-0.27microns of spherical aberration) and partially by AcrySof IQ Aspheric®, Alcon (-0.20microns). Zero spherical aberration IOLs (Akreos AO®, B&L) are useful with subluxated cataracts and decentred pupils. Traditional spherical IOLs with positive spherical aberrations are preferred in post-hyperopic LASIK cases. The newer TECNIS Eyhance® IOL (J&J Vision) has a larger landing zone giving good distance and some amount of intermediate vision.
Pseudoaccommodative IOLs are a popular choice for patients who want greater freedom from glasses. The new trifocals provide good intermediate and near vision with fewer side effects. Trifocals such as the AT Lisa (Zeiss), FineVision (PhysIOL), Alsafit (Alsanza) and Acriva Reviol (VSY Biotechnology) have two add powers at 40 and 80 cm in addition to distance. The quadrifocal, PanOptix (Alcon) has add powers at 40, 60, and 120 cm. Redistribution of intermediate focal point at 120 cm to distance results in its behaving as a trifocal with higher transmission of light (88%) with a 3mm pupil, unlike other trifocals, thereby improving contrast sensitivity and quality of distance vision.
The extended depth of focus (EDOF) IOLs such as Tecnis Symfony (AMO) and AT LARA 829MP (Zeiss) provide an elongated area of focus that extends depth. EDOF IOLs cause less glare, halos, and loss of contrast and give reasonably clear vision at all distances though slightly less for near than trifocals. A micromonovision strategy may be used with EDOFs to attain good binocular vision at all distances. The Tecnis® Synergy is a far to near continuous range of vision IOL that eliminates visual gaps present in trifocal and other multifocals. These IOLs are preferred over multifocals in eyes with maculopathy, irregular corneas, large angle kappa, glaucoma, and in those patients with greater night driving needs.
Newer accommodative IOLs both in-the-bag and sulcus placed, such as Synchrony dual-optic accommodating IOL (Visiogen, Alcon), Tetraflex (Lenstec), 1CU IOL (HumanOptics), Dynacurve IOL (Nulens) may become popular if they can provide safety as well as long term, continuous range of high quality vision without photic phenomena.
Toric IOLs are suitable for patients with astigmatism above 1 D on topography. Since uncorrected astigmatism degrades visual quality, toric versions of pseudoaccommodative IOLs should be used for best results. For less than 1 D of astigmatism, steep axis incision, limbal relaxing incisions, astigmatic keratotomies, or opposite clear corneal incisions work.
CHOOSING IOL POWER
IOL power calculation is crucial when implanting premium IOLs. Multiple, repeatable measurements with different instruments and devices help avoid errors. Variable measurements, irregular patterns on topography, and ocular staining may be indicative of dry eyes and measurements should be repeated after treatment of the dry eye. Consistent IOL power with different newer IOL formulae helps decrease error. Type and magnitude of astigmatism, amount of posterior corneal astigmatism, accurate biometry, and appropriate IOL formulae are all important for toric IOLs. Astigmatism from 0.75 D to 4.75 DC can be corrected using standard toric IOLs, which are available in the range of 1.5 D to 6.0 D cylinder, while higher powers may be made-to-order.
Post refractive surgery IOL power calculation is prone to errors using standard methods. Laser vision correction alters normal anterior/posterior curvature ratio causing errors. Radial keratotomy results in overestimation of routine keratometry value and with 2-variable formulae, also underestimates effective lens position. Various power calculation methods are described for these difficult eyes.
Multi-component IOLs with changeable optic component such as Precisight (IVO) and Harmoni (ClarVista Medical), capsular devices allowing IOL position adjustment like the Gemini Refractive Capsule (Omega), and small aperture IOLs using pin-hole principle—the IC-8™ IOL (AcuFocus) and XtraFocus Pinhole implant (Morcher), the pinhole pupilloplasty technique, Light Adjustable Lens (LAL –Calhoun Vision) and post-operative LIRIC (laser induced refractive index changing (Perfect lens, Perfect Lens LLC) are useful for these and other conditions such as ectatic corneas where IOL power calculation is difficult and has less predictability. Intra-operative aberrometry can also help select power. A technique for ectatic corneas that I personally prefer is two-stage: CAIRS (Corneal Allogenic Intrastromal Ring Segments), a technique described by me to flatten the cornea followed later by cataract surgery.
CHOOSING IOL MATERIAL AND DESIGN
A square edge design helps prevent posterior capsular opacification. Three-piece IOLs are preferred for sulcus placement. Truncated edges, surface reflectivity, and refractive index affect the incidence of positive and negative dysphotopsias, which are reported to be higher with acrylic than silicone or copolymer IOLs. Hydrophobic acrylic IOLs give controlled unfolding. However, all hydrophobic acrylic IOLs are not the same and many properties such as biocompatibility, glistening formation, etc. are affected by component monomers and manufacturing conditions such as thermal history.
Patients with complex pathologies require careful selection of IOL material. Hydrophilic acrylic IOLs should be avoided in patients who may require endothelial keratoplasty or pars plana vitrectomy as intra-cameral/intravitreal gas can cause IOL anterior surface/sub-surface opacification. Similarly, silicone IOLs should be avoided in patients who may require posterior segment surgery to prevent fogging during fluid-air exchange and to avoid persistent silicone oil droplets on the posterior IOL surface even after oil removal. Silicone IOLs may develop calcification of the posterior surface in eyes with asteroid hyalosis even without a broken PC. In-the-bag acrylic and heparin surface modified PMMA IOLs cause lower post-operative inflammation in patients with uveitis.
Blue and violet blocking chromophore IOLs may help prevent retinal phototoxicity. Since blue light is also needed for colour vision, night vision, sleep and circadian rhythms, selective violet-light filtering chromophore IOL combined with sunglasses worn during the day may decrease the risk of macular degeneration. Photochromatic IOLs (Matrix Aurium; Medennium) have also been developed which remains colourless indoors but turn yellow in the sunlight.
Finally, it will be interesting to see how the newer technology IOLs such as SmartIOL (Medennium), FluidVision (PowerVision), Juvene (LensGen), Sapphire IOL (Elenza), Dynacurve IOL (NuLens), Lumina lens (Akkolens/Oculentis) play out in the future.
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 firstname.lastname@example.org.