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Ongoing development of increasingly customized IOLs provides an ophthalmic surgeon with the means to offer refractive cataract surgery patients a lens or a combination of complementary lenses that specifically address their individual needs.
Ongoing development of increasingly customized IOLs provides ophthalmic surgeons with the means to offer refractive-cataract surgery patients a lens or a combination of complementary lenses that specifically address their individual needs. Based on my recent experience, the first aberration-free accommodating IOL with aspheric optics (Crystalens Aspheric Optic [AO] IOL, Bausch + Lomb) epitomizes that trend.
The lens combines the accommodative architecture that this brand is known for, with an anterior and posterior aspheric surface optic that eliminates the induction of spherical aberration. The result is a lens that takes a step forward in terms of quality of vision and predictability in comparison to its Crystalens predecessors, without sacrificing the extended range of focus. The new optics incorporate uniform center-to-edge power so optical performance is less affected by pupil size, optic decentration, or tilt. This enhances quality of vision with minimal loss of range of focus.
When a patient chooses Crystalens, the AO is our model of first choice. We typically implant the lens in the dominant eye first if vision is similar between eyes in patients with cataracts. Most patients receive the same lens in their second eye, but I have had excellent success combining the aberration-free accommodating IOL with aspheric optics with a Crystalens HD in the nondominant eye. The Crystalens HD, while a little less forgiving due to its bispheric design, still has a place in my practice because of the increased reading vision and range of focus it provides. Understanding a patient's needs and lifestyle demands is critical in determining what type of lens to implant.
As with all Crystalens models, accurate preoperative measurements and astigmatism assessment are paramount. To maximize biometry readings, consider the use of a proprietary diagnostic system (IOLMaster, Carl Zeiss Meditec) to obtain keratometric readings before any eye drops, applanation, or corneal manipulation; if you do not have this device, then use immersion ultrasound to determine axial length. Take note of any dry eye or other ocular pathology that may affect the corneal surface. For contact lens wearers, ensure that contact lens use has been discontinued long enough to provide corneal stability. If necessary, it can help to take two readings 1 week apart showing stable measurements before accepting the final measurement for IOL calculations.
To ascertain accurate lens power calculations, the SRK-T formula should be used for eyes with axial lengths measuring 22.01 mm or more. The recommended starting A constant for the aberration-free accommodating IOL with aspheric optics is 119.1. The Holladay II formula should be used for eyes with axial lengths measuring 22 mm or less, and is suggested for eyes with K measurements flatter than 42 D or steeper than 47 D independent of axial length.
When identifying the optimal refractive target, select a lens that predicts between plano and –0.25 D in the distance eye and a lens that targets between –0.25 and –0.50 D in the near eye. Naturally, the lens power selection may have to be adjusted based on the refractive outcome of the first eye.
Ideal outcomes also are dependent on reducing any residual astigmatism to less than 0.50 D. It is important to ensure that the capsulorhexis is properly sized in the range of 5.5 to 6 mm, and that there are no tears or weak zonules.
Optimization of the ocular surface also is recommended. Preoperative assessment using tear break-up time and Schirmer testing can help plan treatment course. Artificial tears, topical cyclosporine, topical azithromycin, and oral agents (such as doxycycline and omega-3 fish oils) all are useful tools.
Postoperatively, maintaining a longer course of steroids is an effective way to avoid fibrosis and capsular contraction. The ultimate goal is to optimize the accommodative amplitude and enhance near vision outcomes. We treat our patients with 8 weeks of topical steroid and non-steroidal anti-inflammatory drops. We find that this therapeutic course reduces capsular fibrosis and maximizes capsular elasticity. This postoperative regimen can help to stabilize the refraction of the eye, and it also reduces the risk of cystoid macular edema.
Y. Ralph Chu, MD, is founder and medical director of Chu Vision Institute, Minneapolis. He is a consultant to Bausch + Lomb.