What if developers from a surgical device company actually asked an optometrist to design his or her ideal intraocular lens (IOL)? No, I’m not talking about one of those “Ph.D./O.D., optics guru-type” optometrists. I’m talking a real optometrist––one who has to fix broken toilets, fight with VSP, fit contacts, coach little league and refer patients for cataract surgery.
If given this opportunity, I’d be willing to bet that a majority of optometrists would be interested in designing a “premium monofocal IOL.” Although we have been thoroughly saturated with information about the advantages of multifocal and accommodating IOLs during the last decade, they simply aren’t appropriate for every individual.
O.D.s Want an IOL to:
Many patients, for example, are turned away by the potential for significant night glare or reduced contrast sensitivity. And let’s face it, in daily practice, most O.D.s see significantly fewer patients with multifocal/accommodating IOLs than single-vision lenses, anyway.
During the last five years, a variety of advanced monofocal IOLs have become available in the U.S. Many of these lenses have been designed to reduce the incidence of common postoperative problems, such as inflammation, posterior capsular opacification (PCO) and spherical aberration (SA). This article provides a review of the features that O.D.s should be most interested in when counseling a patient on monofocal cataract surgery.
What O.D.s Want
It’s no big secret––when it comes to cataract procedures, eye surgeons chiefly are concerned about the insertion technique, incision size, and how the IOL will sit in the capsular bag. While those surgery-related considerations may be somewhat relevant to a comanagement specialist, most O.D.s likely have a markedly different list of associated concerns.
Without question, optometrists chiefly are interested in the postoperative outcome and care of cataract surgery patients. More specifically, we want enhanced lens biocompatibility, improved optics and excellent postoperative safety.
Enhanced Biocompatibility
As an optometrist, the first feature I’d want in an IOL is biocompatibility. In short, I want the patient’s eye to “play nice” with this new piece of plastic.
For our purposes, biocompatibility can be assessed by measurements of uveal compatibility (which relates to inflammation within the eye) and capsular bag compatibility (which relates to PCO). It is important to note that these lens aspects are inversely proportional.
Typically, hydrophilic lenses exhibit greater uveal compatibility than hydrophobic lenses. Unfortunately, however, hydrophilic lenses have been shown to have a higher PCO rate than their hydrophobic counterparts.1 Recent studies of newer hydrophobic acrylic IOLs have shown that they do not create significantly more inflammation than hydrophilic lenses, even in eyes at an increased risk (e.g., patients with pre-existing uveitis).2 Therefore, more surgeons are now leaning toward the implantation of hydrophobic acrylic lenses, which have very low rates of inflammation and PCO.
Today, we also are witnessing improvements in the biocompatibility of the lens capsule. Accordingly, PCO rates continue to decline as IOL designs and materials improve.
There are several ways in which surgeons can help reduce PCO in single-vision cataract surgery patients:
• Lens material. In one recent study of rabbit eyes, Bausch + Lomb’s enVista IOL exhibited a trend toward lower PCO rates.3 The enVista lens, which recently received FDA approval in June 2012, is made of hydrophobic acrylic material with a 4% water content. It is important to note that this lens demonstrates both reduced inflammation levels and lower PCO rates––effectively combining the typical benefits of both hydrophilic and hydrophobic lens materials.3
• Lens design. In a 2012 study published in the Journal of Cataract and Refractive Surgery, researchers at the John A. Moran Eye Center in Salt Lake City evaluated a modified, one-piece, hydrophilic acrylic monofocal IOL (Zephyr, Anew Optics) that incorporated haptic perforations between the peripheral rings.4 The researchers determined that the IOL design produced low amounts of capsular bag opacification.4 They hypothesized that an open capsular bag enhances endocapsular inflow of aqueous––thus reducing PCO.4
Further, it appears that an IOL’s edge design has a direct impact on the amount of postoperative PCO. Many studies have shown that a square-edge or sharp-edge design yields a reduction in PCO.5 A mathematical model indicated that a square-edge IOL exerts 60% to 70% more pressure on the posterior capsule at the optic edge than a round-edge IOL.5 Also, it appears that sharp edges provide a physical barrier to lens epithelial cells as they migrate within the capsular bag.
• Surgical improvements. One additional way to marginalize the impact of PCO is via improvement of the surgical procedure itself. A consistent, uniform overlap of the anterior capsule and the IOL edge prevents epithelial cells from migrating beyond the edge of the lens. Femtosecond lasers used in cataract surgery create a more circular capsulorhexis, which could create a regular seal at the IOL edge and potentially reduce PCO rates. But, because femtosecond cataract surgery in the United States still is a relatively new procedure, published study data is somewhat limited.
In another recent study in the Journal of Cataract and Refractive Surgery, researchers documented less PCO in patients who underwent small-incision cataract surgery than in patients who had a micro-incision procedure.6 The advantage of micro-incision cataract surgery is a tendency for less postoperative astigmatism. But, with increased use of femtosecond lasers and toric IOLs, postoperative astigmatism likely will become less of a concern during the next several years.
Improved Optics
Following enhanced biocompatibility, I want a monofocal IOL with excellent optics. Because we are considering only single-vision IOLs, the most important variables are how effectively the device addresses spherical and chromatic aberrations as well as postoperative astigmatism. Wavefront analysis has increased our knowledge of the eye’s refractive properties. Specifically, spherical aberrations have been shown to reduce contrast sensitivity in both phakic and pseudo-phakic patients.7
• Spherical aberration. Current technology can measure the amount of SA that is attributed to the cornea vs. the lens using corneal topography and wavefront aberrometry technology. This data can be used to determine the required amount and type of SA to correct for during the implantation of an aspheric IOL. In this instance, the surgeon’s primary goal is to achieve an optimum SA in the given eye, which will translate to maximal contrast sensitivity.
Today, we know that the cornea has positive SA that does not vary with advancing age. On average, corneal SA has been reported to be +0.27µm in patients with pupil diameters of 6mm.6 Different IOL manufacturers have designed monofocal lenses that neutralize a fixed amount of SA. For example, the Acrysof IQ Aspheric (Alcon) provides 0.20µm of SA; the Tecnis 1-Piece (Abbott Medical Optics) provides 0.27µm; and the SofPort AO Aspheric (Bausch + Lomb) provides 0.00µm.
It appears that, for the aforementioned IOLs to make a difference, the patient must exhibit a pupil diameter greater than 3mm.9 By neutralizing SA, patients can achieve a better quality of vision––especially for night driving. It is worth noting that the Tecnis 1-Piece was tested specifically in night driving situations, and was shown to yield better vision function than traditional, non-aspheric IOLs.10
• Astigmatism. While it is nice to reduce the number of higher-order aberrations following cataract surgery, patients still require––and often demand––precise correction of lower-order aberrations to be happy with their postoperative visual outcome.
During the last 15 years, optometrists have come to realize that astigmatism correction is fundamentally critical to the success of cataract surgery. To put this consideration in better perspective, imagine only being able to use spherical contact lenses in your patients. Many patients would report that their vision was completely inadequate.
Today’s advanced monofocal toric IOLs can correct more than 4.00D of astigmatism in the corneal plane. Because the crystalline lens is removed during a cataract procedure, it is important to evaluate corneal astigmatism––not lenticular astigmatism.
Currently, Alcon’s Acrysof IQ toric is one of the leading astigmatism-correcting IOL on the market. It is comprised of the same materials as other IOLs in the Acrysof portfolio, and has been shown to exhibit very little rotation within the capsular bag.11,12 Therefore, as an optometrist recommending this IOL, I do not have to worry about lens rotation in the same way I might with a contact lens.
To determine the appropriateness of the Acrysof IQ toric, the surgeon uses an online lens calculator, which accounts for the incision site, size, keratometry in determining the proper power, and location of the toric IOL. For patients who have more than 0.75D of corneal astigmatism, I’ll often recommend a toric IOL.
Postoperative Safety
Ideally, an IOL will exhibit physiological properties that are at least the same as––if not better than––those offered by our natural lens. Our crystalline lens blocks most UV light within the spectrum of 300nm to 400nm. So, it’s only natural for our patients to expect the same level of light protection from an IOL.
• UV/blue-blocking. There has been considerable debate about whether the blockage of blue light is a benefit or a hindrance to our patients. Fifty-six reports on topics related to blue-blocking lenses, including sleep disturbance, visual outcomes, cataract surgery success, lens transmittance, sunlight exposure and macular disease, were published in peer-reviewed journals from 1962 to 2009.14 Only one independently written article showed a deleterious impact on scotopic vision and circadian rhythms in patients who were fitted with blue-blocking IOLs.14 However, none of the other studies documented any associated complications.14
The primary purpose of blue-blocking IOLs is to protect the macula from harmful light rays associated with macular degeneration. But, what’s up for debate is how effective these lenses are in protecting the retina from blue-light exposure, and/or if completely blocking blue light is, in fact, truly beneficial to patients.15
Clinical science points to a correlation between photo-oxidative stress and macular degeneration; however, published epidemiological studies suggest mixed results.15 Bottom line: The postulation that age-related macular degeneration can be attributed to UV light exposure is seductive, yet still unproven.
So, is there a definitive answer regarding the benefit of blue-blocking IOLs? Personally, I have worked with surgeons who implant both blue-blocking IOLs and clear IOLs. My experience has been that patients who have macular degeneration appreciate the implantation of IOLs that may be more protective of their retinas.
We are living in exciting times for cataract surgery. Several currently available monofocal IOLs easily meet and exceed our patients’ visual and physiological needs. Discussing appropriate single-vision lens options with your cataract patients is an important task, and should be part of your preoperative consultation.
Dr. Owen is a graduate of the Illinois College of Optometry and has a master’s degree in Business Administration from San Diego State University. He is the optometric director of Encinitas Optometry in Encinitas, Calif. and Vice President of Business Development for nJoy Vision.
1 .Saeed MU, Jafree AJ, Saeed MS, et al. Intraocular lens and capsule opacification with hydrophilic and hydrophobic acrylic materials. Semin Ophthalmol. 2012 Jan-Mar;27(1-2):15-8.
2. Tognetto D, Toto L, Minutola D, et al. Hydrophobic acrylic versus heparin surface-modified polymethylmethacrylate intraocular lens: a biocompatibility study. Graefes Arch Clin Exp Ophthalmol. 2003 Aug;241(8):625-30.
3. Ollerton A, Werner L, Fuller SR, et al. Evaluation of a new single-piece 4% water content hydrophobic acrylic intraocular lens in the rabbit model. J Cataract Refract Surg. 2012 Oct;38(10):1827-32.
4. Leishman L, Werner L, Bodnar Z, et al. Prevention of capsular bag opacification with a modified hydrophilic acrylic disk-shaped intraocular lens. J Cataract Refract Surg. 2012 Sep;38(9):1664-70.
5. Boyce JF, Bhermi GS, Spalton DJ, El-Osta AR. Mathematical modeling of the forces between an intraocular lens and the capsule. J Cataract Refract Surg. 2002 Oct;28(10):1853-9.
6. Gangwani V, Hirnschall N, Koshy J, et al. Posterior capsule opacification and capsular bag performance of a microincision intraocular lens. J Cataract Refract Surg. 2011 Nov;37(11):1988-92.
7. Piers PA, Manzanera S, Prieto PM, Gorceix N, Artal P. Use of adaptive optics to determine the optimal ocular spherical aberration. J Cataract Refract Surg. 2007;33(10):1721-6.
8. Beiko G. Measurement of the wavefront aberrations using the Oculus Easygraph Topographic System. Presented at ASCRS Annual Meeting, San Diego: May 2004.
9. Schmidinger G, Menapace R, Pieh S. Intraindividual comparison of color contrast sensitivity in patients with clear and blue-light-filtering intraocular lenses. J Cataract Refract Surg. 2008 May;34(5):769-73.
10. Tecnis foldable posterior chamber intraocular lens. Package insert. Abbott Medical Optics, Inc.
11. Zuberbuhler B, Signer T, Gale R, Haefliger E. Rotational stability of the AcrySof SA60TT toric intraocular lenses: a cohort study. BMC Ophthalmol. 2008 May 6;8:8.
12. Ferreira TB, Almeida A. Comparison of the visual outcomes and OPD-scan results of AMO Tecnis toric and Alcon AcrysofIQ toric intraocular lenses. J Refract Surg. 2012 Aug;28(8):551-5.
13. Qiu X, Kumbalasiri T, Carlson SM, et al. Induction of photosensitivity by heterologous expression of melanopsin. Nature 2005;433:745-9.
14. Henderson BA, Grimes KJ. Blue-blocking IOLs: a complete review of the literature. Surv Ophthalmol. 2010 May-Jun;55(3):284-9.
15. Mainster MA, Turner PL. Blue-blocking IOLs decrease photoreception without providing significant photoprotection. Surv Ophthalmol. 2010 May-Jun;55(3):272-89.
