V. SPECIAL CONSIDERATION FOR SPECTACLE INDEPENDENCE
Recent advances in multifocal and accommodative IOL design have led to a tremendous increase in patient satisfaction with spectacle independence. However, the most critical part of ensuring success with these lenses is the preoperative evaluation. Appropriately identifying patient’s visual goals is always the first step to choosing the best IOL. However, the patient’s goals must be consistent with the capabilities of the patient’s optical system. In the following section, we will discuss objective measurements that can help surgeons determine if accommodative, multifocal, or toric lenses are indicated.
A. The Ocular Surface
The microenvironment of the tear film changes as we age. Ocular surface disease is very common in an older population and the air/tear interface is responsible for 70% of the eyes’ refractive power. Maximizing the quality of the tear film and the ocular surface is critical to IOL performance. When considering these lenses, the surgeon needs to evaluate and treat for dry eye syndrome. Objective testing includes tear breakup time, Schirmer testing, osmolality testing, and physical exam. Treatment regimens including cyclosporine, omega-3 fatty acids, punctal occlusion, topical azithromycin, and others can help maximize quality of the ocular surface.
B. Corneal and Lenticular Astigmatism
Multifocal IOLs or accommodative IOLs are very sensitive to even mild amounts of astigmatism and the surgeon needs to try to limit the post- operative astigmatism to less than 0.5 diopters. For mild astigmatism, the surgeon may simply choose to operate on the steep axis to reduce astigma- tism to acceptable levels. If mild-to-moderate amounts of astigmatism are present, a concurrent limbal relaxing incision or astigmatic keratotomy can be performed to reduce the astigmatism. In patients with high amounts of astigmatism, the toric IOLs are the best option for achieving good distance vision. Although these lenses do not correct for presbyopia, patients can still achieve spectacle independence through targeting a monovision with these toric lenses. If residual astigmatism is present postoperatively, excimer laser treatment is the most accurate way to remove residual astigmatism. However, if the spherical equivalent is near plano, astigmatic keratotomies or limbal relaxing incisions can be used to decrease the astigmatism.
C. Topography and Tomography
Irregular astigmatism has a tremendous effect on the ability of presbyopia- correcting lenses to function well. Topography is important in all patients undergoing presbyopia-correcting lenses to make sure that irregular astigmatism is not present and to quantify and confirm the amount of regular astigmatism that is present.
D. Higher-Order Aberrations
Irregular astigmatism, anterior basement membrane dystrophy, and other factors can cause higher-order aberrations. Because both presbyopia- correcting IOLs and higher-order aberrations decrease contrast sensitivity, it is important to avoid multifocals in the setting of excessive higher-order aberrations. Wavefront aberrometers are able to predict how much of the higher-order aberrations come from the corneal surface and avoid multifocals in such scenarios. For example, the Nidek OPD III scan can perform this function and if the root means square is greater than 0.3, multifocals are generally avoided.
E. Angle Kappa
Angle kappa is the distance between the center of the pupil and the visual axis. If angle kappa is greater than half the diameter of the central optical zone of a multifocal IOL, the primary path of light may traverse one of the multifocal rings instead of the central optic, leading to unwanted glare. The ReSTOR 3.0 lens has a central optical zone of 0.8 mm and a Tecnis multifocal has a central optical zone of 1.0 mm. Therefore, an angle kappa of less than 0.4 for the ReSTOR (Alcon Laboratories) 3.0 or 0.5 for the Tecnis (Abbott Medical Optics) multifocal is probably acceptable (Figure 2-4).
F. 3-mm and 5-mm Refractive Zones
Patients can experience a phenomenon known as night myopia that is due to the increased curvature of the peripheral cornea. This is particularly true in patients who have had prior refractive surgery with smaller ablation zones. Instruments such as the Nidek OPD III scan and the iTrace (Tracey Technologies) systems can measure refractions at differing optical zones. If the 3-mm and 5-mm optical zone is different, then presbyopia-correcting lenses are of- ten avoided (Figure 2-5).
G. Optical Coherence Tomography of the Macula
Trying to achieve spectacle independence after cataract surgery is depen- dent on a healthy macula. Although a good funduscopic exam can pick up most subtle pathology of the macula, sometimes a small change in the foveal contour or an epiretinal membrane or posterior vitreous detachment or a subtle subfoveal drusen is picked up on optical coherence tomography (OCT) while missed on the exam. In these settings, we often avoid presbyopia- correcting lenses.
H. Ability to Use Laser Vision Correction in the Future
Despite the best preoperative evaluation and IOL calculations, a small percentage of patient will not achieve the refractive goal. The surgeon should consider any possible contraindications to laser vision correction prior to implanting a lens to minimize spectacle independence.
*Dikutip dari Buku Essentials of Cataract Surgery 2nd Ed, halaman 20-23