The National Eye Institute (NEI) projects that by 2050, the amount of people in the US with cataracts will double to 50 million. Expectations are also on the rise for refractive outcomes as cataract surgery evolves into a solution for refractive conditions. This article will review the different IOLs available for cataract surgery, one of the many technologies now available to refractive surgery patients.
As primary eye care doctors, it’s important for us to discuss the refractive aspect of cataract surgery with our patients before their consultation with the surgeon. This allows them to understand the different options available so they are more educated on their future visits. Patients need to be educated on traditional vs laser surgery, and different intraocular lenses (IOL): monofocal, toric, multifocal, trifocal and extended depth of focus. Setting up expectations prior to surgery makes postoperative management easier.
Laser vs Traditional
Femtosecond laser technology (FSL) has been available since 2010. There are advantages and disadvantages to this technology. The purpose of FSL assisted cataract surgery (FLACS) is anterior capsulotomy creation, lens fragmentation, and accurate corneal incisions (especially to control corneal astigmatism). There are some contraindications such as corneal scarring (ex. arcus), mature cataracts, and small pupils < 5mm (may use rings or iris hooks). However, the FEMCAT study suggests that there is no statistical difference in postoperative refractive and visual outcomes with manual vs FLACS.
Some doctors prefer FLACS for maximum refractive outcomes, since it provides limbal relaxing incisions and centered capsulotomies that make it easier to center premium lenses. Surgeons prefer FSL when dealing with complicated cases such as Fuchs endothelial dystrophy (less phaco energy used inside the eye), white cataracts, pseudoexfoliation, or floppy iris syndrome.
I have advised patients that laser versus manual will both remove the cataract, but vision postoperatively may vary to the accuracy and precision of pennies vs quarters. Most patients prefer lasers over traditional, just due to the idea of a laser making incisions versus a blade. And in choosing a premium lens, some surgeons may include FLACS in the bundle cost instead of an ad on.
If a patient has less than 1D of corneal astigmatism, they are not a candidate for toric IOLs. The lowest cylinder amount that can be corrected in a toric IOL is at least 1.5D and can go up to 9.0D. If they have less, a standard monofocal lens should suffice. Toric IOLs have come a long way in better postoperative rotation stability. Preoperatively, corneal astigmatism can be measured with various techniques from manual to automated keratometry.
Key points to note are that with age, astigmatism increases and moves more towards becoming more against-the-rule (ATR). So in calculating the IOL power, corneal astigmatism can be decreased by ~0.5D in with-the-rule (WTR) astigmatism and increased by ~0.3D in ATR. Surgically induced astigmatism (SIA) can also be a factor depending on the corneal incision, location of the incision, patient age, and amount of preoperative astigmatism. There are several programs available to surgeons from lens manufacturers to help calculate IOL powers and personalized SIA.
Most toric IOL implants only have a small amount of residual astigmatism. Astigmatism less than 1D is noted in up to 88% of cases, and less than 0.5D in 67% of patients. Approximately 60-80% of patients boast spectacle independence for distance vision. The average rotation of the IOL is noted at 5 degrees or less.
Multifocal IOLs either refract, diffract, or do both. Here’s a summary table to understand the overall difference between these two designs:
|Lens Design||Several optical zones on the IOL||Gradual diffractive steps on the IOL creating smoother transition between focal points|
|Vision||Best for intermediate and distance vision. Small print may be difficult.||Best for near and distance vision. Fair intermediate vision.|
|Pupils||Dependent (>3mm diameter)||Less dependent|
|Contraindication||Those who read for long periods of time or in poor lighting may experience eye fatigue||Not ideal for those with increased computer work|
|Examples||ReZoom, Array||Tecnis, Restor, PanOptix|
These IOLs provide visual correction for distance, intermediate, and near. The new PanOptix has focal points at optical infinity, 60cm and 40cm, and what makes it unique is the amount of incoming light it utilizes. Other lenses available are the Restor 2.5 and 3.0.
Another option is an accommodative IOL which mimics the eyes’ natural ability to process accommodation. The lens has hinges that are connected to the ciliary muscle in a way that it moves forwards or backwards when the muscle contracts. This changes the focal points allowing the eye to focus at various distances. However, these IOLs have lower and varying amplitudes of accommodations, and have been known for unstable refractive outcomes.
Examples include Crystalens AO and Trulign Toric.
Extended Depth of Focus IOLs
These implants use chromatic aberration to create smoother transitions between optical zones, and fewer “dead zones” where vision is non-functional between focal points. It can provide around +1.50D of range, therefore requiring patients to rely on readers for smaller print or threading etc. Patients may have better contrast sensitivity and less aberrations, but higher levels of dysphotopsias (haloes, glare, starburst).
An example of such a lens is the Tecnis Symfony.
Toric Multifocal IOLs
These IOLs provide multifocal correction with astigmatism. In the preoperative assessment, it is crucial to correctly estimate the amount of corneal astigmatism and rotational stability. The rate of satisfaction with this procedure is greater than 84%.
Common lenses are the Restor and the newer PanOptix (unique technology that uses more incoming light).
Stated as the only lens that can be modified AFTER cataract surgery. The IOL is made of photoreactive ultraviolet absorbing material that can be customized using a light delivery device (LDD) in-office after surgery. The device is approved for post operative residual spherical values of up to 2D, and residual corneal astigmatism from 0.5-3.0D.
This monofocal lens has an aspheric lens design with a broader defocus curve allowing good distance and intermediate vision. The lens has more “sweet spots” compared to current monofocal options. The advantage is a decrease in diffractive haloes and better contrast sensitivity.
This is another monofocal lens but with an embedded pinhole allowing an extension of light rays to focus in the eye providing an expanded depth of field. The principle is similar to the Kamra inlay that only allows central, focused light to reach the retina filtering out peripheral defocused light. It may be used in irregular corneas. Clinical trials are being conducted that should complete in May 2020 in the USA.
This is a very future forward idea: this artificial capsule is implanted into the eye to create an environment for an array of ophthalmic options like IOL implantation, medication delivery, or even augmented reality technology!
It all starts with setting expectations before surgery. The most common postoperative complication is residual refractive error. Once the cornea has stabilized, patients can elect to have enhancements with LASIK or PRK. Patients often hear stories from their families, friends, or people in line at the grocery store or gym about how they no longer “need glasses” after surgery. We know everyone’s unique! So we need to do a better job informing our patients. Understand their hobbies, work life, day-to-day habits to determine what the best solution for them would be.
Many IOLs come with a compromise so there is somewhat of an “art” to choosing the right one or combination of two. Let your monofocal IOL patients know about the dependence on reading glasses. If you have a myope, they are probably used to seeing near, and may be happier with a slight myopic correction post surgery. Those with increased demand for distance vision (truck drivers, emmetropes, photographers, hunters) will likely prefer a monofocal or astigmatic correction vs presbyopic correction due to lower contrast sensitivity, and postoperative haloes.
It is never too early to start having these conversations. Discussing over the course of 2-3 visits allows patients to understand their options and targets the point home. Some may need a head start to start saving for premium options as well.
It is truly such a life changing experience for older (and younger) patients especially when we are able to decrease their dependency on glasses and improve eyesight as a whole. As F. Scott Fitzgerald wrote:
“The world only exists in your eyes. You can make it as big or as small as you want.”