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Key steps ensure success with toric IOL implantation
A specialist offers pearls for maximizing surgical results when correcting astigmatism during cataract surgery.
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Cataract surgery has advanced considerably, with surgical techniques that offer smaller entry incisions on the cornea, foldable IOLs that can correct astigmatism and presbyopia, better viscoelastic materials, precise and reproducible laser-assisted capsulorrhexis, and advanced phaco technology. All of these advancements have moved cataract surgery to a different platform, a higher level of precision that often translates to better quality of vision postoperatively and higher patient satisfaction.
In the era of targeting optimal visual quality after cataract surgery, we need to consider the impact of ocular wavefront aberrations. Ocular aberrations degrade the overall visual quality due to their effect on retinal image quality. Ocular wavefront aberration represents the difference between the ideal and actual wavefront. While lower-order aberrations such as myopia (positive defocus), hyperopia (negative defocus) and regular astigmatism contribute to 90% of the overall ocular wavefront aberration, the higher-order aberrations (eg, coma, trefoil and spherical aberration) only contribute to the remaining 10% of the overall ocular wavefront aberration. Using a toric IOL effectively decreases postoperative astigmatism and improves uncorrected visual acuity, thus contributing to overall patient satisfaction. However, we need to continue clinical studies on wavefront aberrations associated with toric IOLs. Any induced postoperative wavefront aberrations should be monitored, and any effect on overall postoperative visual acuity should be followed over time.
Thomas John
In this column, Black provides a number of useful clinical and surgical pearls that can help achieve optimal results following the use of a toric IOL.
Thomas John, MD
OSN Surgical Maneuvers Editor
A large-scale study of cataract patients by Ferrer-Blasco and colleagues demonstrated that 34.8% of eyes have greater than 1 D of corneal astigmatism. Surgeons have employed a variety of means to correct astigmatism during cataract surgery, the most common being limbal relaxing incisions. However, evidence shows that arcuate keratotomy significantly increases the potential for both higher- and lower-order aberrations. In addition, studies have shown that toric IOLs are more effective at correcting corneal astigmatism than limbal relaxing incisions. While some surgeons may be hesitant to use toric lenses, following a couple of key steps will help to ensure a successful surgery.
Daniel A. Black
IOL selection, biometric evaluation
When presented with a cataract patient, a surgeon’s first thought is what lens to use. Among the astigmatism-correcting IOLs, the Tecnis toric IOL (Abbott Medical Optics) differentiates itself due to its ability to reduce overall spherical aberration as well as reduce chromatic aberration. These two characteristics contribute to Tecnis being in a unique position compared to other platforms.
In my practice, when patients make appointments, we try to flag the files of those who may have cataracts so that biometry is the first test we perform when they arrive at our office. If we do not realize that someone is a cataract patient until they have had their pupils dilated and cornea applanation performed, we will have them come back another day to perform their biometry tests. If the cornea applanation is performed, topical anesthetic is instilled and the patient is dilated before the physician determines that biometry should be done, at this point the tear film is very unstable and the biometry results will not necessarily be accurate.
Once the lens is selected, the surgeon must consider how to use this technology to get the best results. The cornerstone to any successful procedure is good biometry. It is very important to remember that with biometry, you are not measuring the actual physical curvature of the cornea, but rather the reflection from the tear film. This makes it imperative that biometry is performed with the best tear film possible.
Lens power calculation
The second step is IOL power calculation. Most major companies have their own online calculators, so determination of which power of lens to use is pretty straightforward, as long as the biometrical data is transcribed correctly. This may seem basic, but typographical errors can happen very easily. I use a program that uploads the biometric measurements directly into my calculator, ensuring there is no risk of transcription error.
The surgery itself is straightforward and only requires meticulous surgical technique. In particular, the axis of astigmatism must be marked while the patient is in an upright position to minimize error from cyclotorsion, and the capsulorrhexis must be correctly centered and sized. The IOL must be in the bag and have a fairly uniform 360° overlap to ensure predictable results. The femtosecond laser can provide consistency with size and centration of the capsulorrhexis. In the absence of a femtosecond laser, you can use a capsulorrhexis marker.
IOL implanted in the bag with 360° overlap of optic by the capsulorrhexis.
Images: Black DA
Drops and applanation disrupt the tear film. It is imperative that biometry be performed with the best tear film possible.
Axis marking. The axis of astigmatism must be marked with the patient in an upright position to minimize from cyclotorsion, and the capsulorrhexis must be correctly centered and sized.
Final steps
The last step during surgery is to ensure that all ophthalmic viscosurgical device used is removed from behind the lens. Leaving any behind can possibly disrupt the orientation of the lens.
After surgery, it is important to perform a very thorough postoperative refraction once the eye has stabilized. This allows the surgeon to get feedback and audit the surgical results. Unless you are tracking your results, you will not know how a particular surgical technique or lens performs for you. In my practice, we have all postoperative examinations done by the same technician, in the same lane. This creates a standard endpoint that allows us to determine if one lens is superior to another or whether a specific surgical technique is having an impact on our results.
In my practice, approximately 40% of patients that come in for routine cataract surgery receive a toric lens. In the same vein that an optometrist would not prescribe glasses that did not correct a patient’s astigmatism, I feel that all cataract patients should have their astigmatism corrected at the time of surgery. While one should never be complacent when performing surgery, it is important to note that there is some leeway with placement of toric lenses. My experience coincides with the data published by Alpins, which show that if the lens is placed 10° off axis, the result will be a loss of about 6% of the effect. This contradicts the common myth that every 1° of misalignment represents a 3% loss of effect.
Good biometry and attention to detail are the key requirements for success with any cataract surgery, and it is no different when implanting a toric IOL. I have performed nearly 1,000 cases and not been disappointed with the results. Once you are in the mindset of “I can do this, and it’s going to work well,” you will find toric lenses to be an excellent option for your patients. Just do not forget the importance of good biometry.