Until recently, the main focus of cataract surgery has been to offer patients a safer, less traumatic procedure with few complications. Today, cataract surgery has evolved to such a level.
But, with this advancement comes an increased emphasis on the visual outcomes of successful cataract surgery. Thus, greater responsibility falls to optometrists to assume an aggressive role in shaping the refractive outcomes of cataract surgery.
Each of us must understand the wide assortment of choices that patients have when contemplating cataract surgery, so that we can be sure that our patients will achieve the most satisfactory visual outcome. So, your most important recommendation for your patients, other than a cataract surgeon, may be their intraocular lens (IOL).
Here, well review the increasing menu of intraocular lens options currently available.
Monofocal IOLs
These lenses provide a certain comfort level. After all, they have been around since Sir Harold Ridley first advocated their use in 1950, and they have remained relatively unchanged since then.
For many patients, these lenses may still be the best option. Monofocal lenses are an excellent choice in that they are stable, and they have a low rate of visual complications. In the correct power, monofocal lenses provide patients with excellent distance visual acuity and few symptoms of glare, halos or night vision problems.
As monofocal lens technology has evolved, advances in lens design have made these lenses easier to insert. Also, they achieve accurate lens position, and they can be inserted through increasingly smaller incision sizes. These lenses are likely to be used successfullyeven by surgeons with limited cataract surgical volume.
Refracting Pearls for Multifocal IOL Patients Do not rely on auto-refraction to determine the sphere. Push plus. Do not have the lights set too dim or too bright. On retinoscopy, expect a slightly hazy view and scissors-effect, similar to post-radial keratotomy patients. Use small narrow streaks to minimize the scissors effect. Use the red/green technique to confirm that the patient is not over-minused. (See Instructions for Red/Green Technique, below.)
Aspheric IOLs
As the human eye ages, nuclear and cortical lens changes diminish the amount of negative aberration in the crystalline lens and leave the eye with increasing positive spherical aberration. This may be partially responsible for a cataract patients symptoms of glare, halos and reduced contrast sensitivity. Removal of the crystalline lens and implantation of a spherical IOL with its own positive spherical aberration, however, leaves the patient with undesired positive aberration.
Today, two IOLs that help correct spherical aberration are available: the AMO Tecnis Z9000 and the Alcon AcrySof IQ. The Tecnis and the AcrySof have inherent negative spherical aberration to compensate for the positive spherical aberration in the average cornea. The result: reduced or eliminated spherical aberration, which leads to better subjective vision.
Also, the AcrySof IQ uses blue-light filtering chromophores to increase contrast sensitivity. This feature gives the AcrySof family of IOLs their characteristic yellow tint.
Two other aspheric IOLs awaiting approval in the
The Centers for Medicare and Medicaid Services (CMS) designated the two available lens designs as New Technology IOLs (NTIOLs), allowing a higher rate of reimbursement for facilities that use them. CMS based this on the results of more than 30 studies that clearly demonstrate an improved quality of vision and contrast sensitivity.
Also, the FDA has said that the Tecnis IOL reduces spherical aberrations, improves night driving and improves functional vision (the ability to see clearly under various lighting conditions). Clinically, this translates into improved patient safety, quicker reaction times while driving at night, and an overall increase in quality of life compared to traditional monofocal IOLs.
Preoperative Data No matter what type of IOL design the patient receives, the surgical outcome and the patients ultimate happiness with the postoperative result depend on accurate preoperative data, which determines the proper lens power. Most postoperative refractive errors should be within 0.25D to 0.50D of the planned result. Refractive history. An understanding of the patients refractive history offers an appreciation for the patients habitual refractive state. Visual function. An assessment of the patients visual demands and desires is an important part of any pre-surgical evaluation. This helps determine if a patient is ready to undergo cataract surgery. Several visual function surveys, such as the VF-14 or the VF-25, can help you and the patient set visual goals. Refractive error. An accurate refraction of all preoperative patients is vital for preoperative IOL planning and determining best-corrected acuity. Keep in mind that the cataract may change the patients refractive error. Keratometry. There is a one-to-one dioptric relationship between keratometry and postoperative refraction, so inaccurate keratometry readings will cause a visually significant error in the IOL calculation. To obtain consistently accurate keratometry readings, check the calibration of your keratometer regularly. Biometry. To achieve optimal refractive outcomes, biometry must be extremely accurate. Incorrect measurement of axial lengthseven by as little as 0.3mmwill result in a postoperative refraction of about 1.00D different than the planned refractive aim.
Todays IOLs demand precise preoperative measurements, consistent IOL formula calculations and predictable results.
Here are the essential elements of the preoperative examination that will guide the selection of the proper lens power:
Optometrists that perform their own preoperative A-scans should use either an IOL Master or an immersion ultrasound device to obtain the most accurate axial length measurements. Traditional contact biometry, in almost all cases, will measure a slightly shorter axial length secondary to corneal compression, which will lead to an unwanted residual refractive error.
IOL regression formula. Various regression formulas can be used to calculate the selected IOL power from the preoperative data. While the SRT-T formula for calculating IOL powers is probably the most widely used, it tends not to be as accurate as the Holladay II formula for hyperopic refractions or short axial lengths.
Each of these variables must be carefully measured to accurately determine the proper IOL power. Even small inaccuracies can result in a postoperative refractive surprise and leave the patient unhappy with the outcome. Also, realize that most surgeons will have their own preference when it comes to lens material, basic design, manufacturer and delivery system.
Toric IOLs
Surgeons have managed significant preoperative astigmatism in various ways. The most common approach: use of astigmatic limbal relaxing corneal incisions (LRIs) at the time of cataract surgery. But, there are several disadvantages to this approach. For example, LRIs:
Increase the amount of time needed for patient refraction to stabilize post-op, sometimes up to two months or longer.
Can aggravate pre-existing dry eye and may increase postoperative discomfort.
Achieve only a limited amount of actual astigmatic reduction. Even this limited amount varies, since results are directly related to surgical technique.
Toric IOLs are designed to neutralize preoperative corneal astigmatism themselves. For example, STAAR Surgical manufactures a plate haptic silicone lens with a cylinder of -2.00D that corrects -1.40D at the corneal plane, or a cylinder of -3.50D that corrects
-2.30D at the corneal plane.
Though these IOLs have been used successfully for years, they may rotate in the capsular bag after implantation, decreasing postoperative acuity. The patient may then need a second surgical procedure to rotate the lens back into proper position. A small amount of IOL rotation can begin to reduce its neutralization of astigmatism, and at 30 degrees of rotation, the astigmatism-correcting effect is completely neutralized. Beyond 30 degrees of rotation, astigmatism may actually increase and become greater than preoperative values.
Less than one year ago, the FDA approved the AcrySof Toric IOL (Alcon), available in cylinder powers of -1.50D, -2.25D, and -3.00D. This IOL has a more traditional haptic design, which may reduce lens rotation. Reports show good centration and minimal rotation of the AcrySof Toric when compared with plate haptic designs, so surgeons may prefer this toric IOL over astigmatic incisions.
A new toric IOL currently used in
Toric IOLs seem to be the next logical step in the quest for a
A January 22 ruling by the Centers for Medicare and Medicaid Services (CMS) now allows beneficiaries to choose implantation of an IOL that corrects pre-existing astigmatism at the time of cataract surgery. As with an earlier ruling for presbyopia-correcting IOLs, Medicare provides coverage for conventional cataract surgery and permits the beneficiary to pay for non-covered items and services associated with refractive errors.
Despite our best efforts, patients are occasionally left with residual refractive error after cataract extraction and IOL implantation. There are several options for correcting this, including: Lens exchange. This option is best for patients who have large residual refractive error. The lens is removed and replaced by a lens of different power. If this option is chosen, the procedure should be performed as soon as possiblebefore the capsular bag fibroses, making removal of the IOL difficult. Piggyback IOL. This procedure corrects residual refractive error without having to remove the initial IOL. The original lens remains in the capsular bag, while the piggyback IOL is placed in the posterior chamber in the ciliary sulcus. Refractive surgery. LASIK is more commonly used to correct residual refractive error following cataract surgery.
Options for Correcting Residual Refractive Error
Monofocal Monovision
Cataract surgery that uses monofocal IOLs to provide monovision is a viable option for presbyopic patients who have been successful with monovision contact lenses. But, O.D.s should educate patients about the limits of monofocal IOLs in a monovision arrangementnamely, the loss of binocular vision.
Until there were true presbyopia-correcting IOLs, monofocal monovision was the only way to keep a patient spectacle-free with functional vision at both distance and near following cataract surgery. The binocular vision loss was a welcome trade-off for many patients who wanted to remain independent of spectacles and who were able to adapt to monovision.
In our practice, fewer patients opt for monovision with monofocal IOLs. Still, it may be the ideal place to begin a discussion of IOLs with cataract patients, especially with those who have been successful with contact lens monovision in the past.
Todays presbyopia-correcting IOLs allow monovision patients to achieve similar results as with monofocal contact lensesbut, they remain binocular through their natural range of vision. Unlike refractive surgery patients, however, who can try monovision with contact lenses, those who have cataracts may not benefit from a similar trial; their visual acuity is already compromised by the cataract.
Instructions for Red/Green Technique 1. Reach the end-point of refraction with the best acuity noted. 2. Dim the room lights completely, and go to the 20/60 or 20/70 line with red/green. 3. Ask the patient to tell you on which sidered or green the letters appear blacker and/or sharper. If the answer is green, the patient is over-minused. Add +0.25D until the answer is red or same. If the answer is red, add -0.25D until the answer is same. 4. Go back to the best acuity and double check that the patient can still read. If the patient cant read, give him or her the extra -0.25D back. If that helps the patient to read, then keep that -0.25D. If it makes no difference, dont use it. This is the final refraction.
Accommodating IOLs
The development of accommodating IOLs has generated much excitement in recent years. Not surprisingly, an accommodating lens design has yet to be perfected; among experts, disagreement remains as to the exact cause and nature of presbyopia itself and how the natural crystalline lens works in accommodation. Several lens designs are currently being investigated, and one of them, the Crystalens (eyeonics), is approved for use in the
The Crystalens incorporates a hinge into the plate design, allowing the optic portion of the lens to move in a way analagous to that of the crystalline lens of the eye. Courtesy: Paul M. Karpecki, O.D.
The Crystalens IOL is made of the proprietary material Biosil, which is incorporated into a biconvex silicone plate with a square-edge design. The Crystalens incorporates a hinge into the plate design, allowing the optic portion of the lens to move in the eye in a way analogous to that of the natural crystalline lens.
During near-point activities, accommodation causes ciliary body contraction, which allows the lens optic to move anteriorly. This movement effectively increases the plus power of the lens in true accommodative fashion. When the focal point shifts to distant objects, the relaxation of the ciliary muscle allows posterior movement of the IOL back to its resting position.
Accommodating IOLs offer several advantages. First, the anterior-posterior movement of the optic provides the near-point add for the patient, and as a result, the optic is a single vision design. Therefore, the subjective quality of vision is usually very good, free of the glare and halos that can be seen with multifocal lens designs. Also, an accommodating IOL functions like the natural crystalline lens; there is a continuous range of vision instead of multiple individual focal points.
Some disadvantages do exist, however. The size of the Crystalens optic is small, only 4.5mm in diameter. This can be an issue with patients who have larger pupils or significant pupillary dilation in dim light, which can make them more prone to edge glare. Also, the lens may not move as much or as well as expected, resulting in myopia at distance or a reduced add at near. Recently, the Crystalens has been updated with a larger optic (5.0 mm) and a new redesigned haptic.
Perhaps the most significant disadvantage of the Crystalens accommodating IOL is the maximum near-point add that is usually seen, and the time it takes to reach that maximum. Patients can usually obtain +2.00D to +2.25D of effective near-point add, but it can take months.
The patient must be motivated, as the ultimate success of the lens depends on the patients willingness to do near-point activities to strengthen the accommodative system. Those patients who are looking for an immediate wow-factor may be disappointed initially, but those who are willing to work with the Crystalens usually have a good surgical result in the end, with a range of vision that affords them a high level of spectacle independence.
Several other accommodating lens designs are in the development pipeline and may overcome some of the disadvantages of the current lens designs.
Researchers have found variation in vision quality between an IOL with aspheric optics (B&L SofPORT AO, top) vs. a standard IOL.
Multifocal IOLs
The multifocal IOL options are currently the most widely used method of including presbyopic correction with cataract surgery. Options include:
AcrySof ReSTOR IOL (Alcon). On February 1, the U.S. Food and Drug Administration (FDA) granted approval of the AcrySof ReSTOR for the visual correction of aphakia following cataract surgery in adult patients with and without presbyopia.
One of the two new-generation multifocal IOLs, the AcrySof ReSTOR has a 6.0mm optic that is primarily distance oriented in the main refractive region. Alcon then uses a patented process called apodization to create a diffractive central 3.6mm zone. The apodization process involves a very gradual stepwise blending of 12 concentric rings to redirect light based on lighting conditions and visual demands.
The AcrySof ReSTOR IOL incorporates a process called apodization, a very gradual stepwise blending of 12 concentric rings to redirect light based on lighting conditions and visual demands.
The apodization process is also meant to reduce the amount of perceived glare and halos; it creates a very slow and gradual diffraction of entering light from zone to zone between the 12 rings. This process creates approximately +4.00D of near-point add, equal to about a +3.20D at the spectacle plane.
The ReSTOR lens includes a more immediate range of vision than the accommodating IOLs. The single greatest advantage of the AcrySof ReSTOR is its very good near visionthere is a very high degree of spectacle independence at near.
For some patients, however, the +3.20D effective add may be too much, and patients may need to reduce their usual working distance to see clearly at near. Another disadvantage is inherent in the multifocal design: the perception of glare and halos, especially early in the postoperative period. Rarely is it debilitating, but it is noticeable, even though it definitely does diminish over time.
Weve found that many patients do not complain of glare and halos unless specifically asked. While the ReSTOR offers an intermediate range of vision, this range is definitely not as clear as its near vision.
The ideal candidate for the ReSTOR IOL is an older patient who does not use a computer often, but who does have multiple near-point demands such as reading, puzzles or sewing. This type of patient has done very well postoperatively and shows a very high degree of spectacle freedom.
ReZoom (AMO). AMOs second generation multifocal IOL is loosely based on the companys original Array multifocal IOL platform, but with significant changes. AMO introduced the Array, the initial design for multifocal IOLs, in January 1998. The company no longer manufactures this lens.
ReZoom has a 6.0mm optic like the ReSTOR, but the design of the zones is very different. While the ReSTOR has the diffractive zones in the central 3.6mm of the optic surrounded by the main distance optics, the ReZoom blends five concentric zones throughout the entire optic portion of the lens.
The ReZoom IOL blends five concentric zones throughout the entire optic portion of the lens. Termed Balanced View Optics Technology by AMO, each zone is proportioned to provide good vision across a range of visual demands and lighting conditions.
Termed Balanced View Optics Technology by AMO, each zone is proportioned to provide good vision across a range of visual demands and lighting conditions. For example, the large central zone at the optical center of the IOL is dedicated to distance vision and bright light conditions. The outermost zone is the thinnest and dedicated to distance vision in low light conditions, in which the pupil would be maximally dilated (such as when driving at night). In total, there are three distance zones and two nearpoint zones, with intermediate vision coming from the interfaces between each zone.
The ReZoom provides a more natural range of vision, with very good distance and intermediate ranges overall. Most patients can work spectacle-free at a computer terminal. Near acuity is good, but with an effective add of approximately +2.75D at the spectacle plane, it may not be enough to see fine detail at near. Most patients can function well at near, but some may need a slight +0.75D add for prolonged or extremely fine near work.
As with the ReSTOR, a small percentage of patients will notice glare and halos, but these symptoms tend to diminish over time. The perceived visual side effects may be an acceptable compromise, though, for patients to be able to become spectacle-free most or all of the time.
Patients who may question the results of their surgery are usually quite surprised when a -3.00D trial lens is held in front of the eye, and they are asked to test their intermediate and near visual acuity. When told that the trial lens simulates their visual range with a monofocal lens, they are more likely to feel reassured in their selection of the multifocal IOL.
We find that the ReZoom is the better choice for younger patients who are still active in the workplace or older patients who spend more time on a computer than they spend at near.
We have also had success using a ReZoom in the first eye and letting the patient test his or her range of vision during the first two weeks post-op. If their range is good, and they can read comfortably, then we use a ReZoom in the fellow eye as well. If their near vision is not quite sharp enough, though, we will blend and use a ReSTOR in the fellow eye to boost their near acuity.
One issue common to both multifocal designs: a neurological adaptation period to the lens. A multifocal optical system does not naturally occur in the human eye, and it takes about 12 weeks for patients to fully experience the maximum benefits of multifocal IOL technology and adapt to the visual side effects that they may experience.
Are these IOL technologies perfect? Far from it. The ideal intraocular lens would probably be an accommodating toric IOL that has an aspheric surface. Perhaps that will be available one day. For now, however, the technology currently available can make a patient who is well informed extremely happy with his or her postoperative result.
Our role as optometrists is changing. Whether you personally believe in this expanding menu of IOL technologies or not, you should be able to have an informed discussion with the patients that you refer for cataract surgery and present them with all of their options.
You should discuss your patients visual needs, prioritize them, and explain how todays IOL technologies can help to improve their quality of life.
Dr. Quinn is the president of OMNI Eye Services of New Jersey. Dr. Veliky is the secretary/treasurer of OMNI Eye Services of New Jersey. Neither doctor has any financial interest in any of the companies mentioned in the article.
