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Sunalp YAG laser lens technique can be used to mark corneal axis for toric IOL placement
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Cataract surgery has clearly advanced in technology, surgical techniques, IOLs and ophthalmic viscosurgical devices. This means our patients are seeing much better than their parents did after cataract surgery. With such advances in cataract surgery, there is an expectation of excellent visual quality that the surgeon needs to provide in order to attain postoperative patient satisfaction.
Postoperative visual quality is dependent on multiple factors, including ocular and corneal surface, quality of tear film, clear cornea without significant astigmatism, optimal IOL and absence of vitreous loss. When addressing these medical and surgical variables, astigmatism greater than 0.5 D often comes to the forefront and can play a role in degradation of visual quality. The extrapolated prevalence of astigmatism in the U.S. is estimated at more than 48 million people, based on Census Bureau population estimates from 2004. About 15% to 50% of cataract patients have associated corneal astigmatism. Therefore, astigmatism correction becomes an integral part of cataract surgery if the patient elects to have it surgically corrected. Such correction of astigmatism can be performed either on the cornea or intraocularly using a toric IOL. With the use of a toric IOL, proper IOL alignment to the selected axis is of paramount importance. Various methods of axis marking on the cornea have been developed.
In this column, Drs. Sunalp and Shehu describe their method of marking the axis on the cornea using a Nd:YAG laser and a newly developed disposable corneal lens.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
Because toric IOL alignment on the steep corneal axis is critical to achieve optimal visual acuity, correct reference eye marking pre-surgically is essential for precise alignment. Reference eye marking is necessary to allow for the change in the orientation of the eye from the sitting to the horizontal position (cyclorotation) of the patient during lens implantation. Because cyclorotation averages 3° and because for each degree the patient loses 3.3% of astigmatism correction, the average loss in astigmatism correction would be about 10%; however, in the considerable number of patients in which cyclorotation is 5% or greater, misalignment of the lens would have a significant negative effect on astigmatism correction.
A number of procedures have been devised to mark the axis of astigmatism to align the toric lens correctly. The oldest and the least accurate procedure uses ink. The axis of astigmatism is marked preoperatively at 0°, 90° and 180° meridians with ink; even though marking with ink is inexpensive and simple, it is not accurate because the ink mark is wide, diffuses and may even disappear.
Another method of marking the axis of astigmatism uses cautery to leave a mark. A small probe, the Wet-Field Osher ThermoDot marker (Beaver-Visitec), has been devised and marketed specifically for the purpose of marking the meridian of the eye. Using a cautery mark can be accurate, but it requires special equipment and the cautery may cause pain.
A digital method for marking the eye preoperatively captures a high-resolution image of the eye. A computer with special software detects scleral vessel, iris, pupil and limbus features, measures keratometry, pupillometry and other necessary parameters, and superimposes the image to the patient’s eye image with a tracking overlay so that preoperative features are paired to the patient’s eye to enable surgeon to see markings in real time, thus eliminating the need for manual marking, automatically accounting for cyclorotation, and assisting in the precise centering and alignment of the lens. This method is accurate and simple, but it requires specialized equipment, such as the Verion guidance system (Alcon), that may not be available to many ophthalmologists.
Images: Sunalp MA, Shehu MH
Intraoperative wavefront aberrometry is likely the most accurate means of achieving near-perfect vision after cataract surgery. This technology allows on-demand measurements of lens power, sphere, cylinder and axis, allowing the surgeon at any time during the procedure to assess the quality of vision, evaluate refractive findings, and refine IOL power, cylinder power and IOL alignment in real time. In addition, wavefront aberrometry accounts for both anterior and posterior corneal astigmatism and reduces the incidence of unintended residual postop astigmatism. Studies using the ORA aberrometer (Alcon) have shown that the number of patients who fall outside the intended astigmatic target are reduced by 54% compared with preoperative calculation of cylinder power and axis. Aberrometers are precise and simple, and they offer results superior to other methods of marking the eye; however, the instrumentation required is not available to the majority of ophthalmologists, especially those in a small practice.
To avoid the pitfalls of preoperative marking with ink or cautery, we have devised a method to mark the eye that is available to all ophthalmologists because it uses equipment that is the mainstay of an ophthalmic practice, specifically the YAG laser.
Procedure
A drop of local anesthetic (Ophthaine) is placed on the eye, and the patient is asked to place the chin on the chin rest of the YAG laser. The “Sunalp YAG laser lens” (Figure 1) is placed on the cornea with the lens 90° at 90° of the patient cornea, the YAG laser is focused at the mid-cornea thickness at 270° perilimbal, and with the YAG LaserEx LQP3106 (Ellex) preset at 0 µm, a single laser pulse of 5 mJ to 10 mJ is aimed at 270° with one to three pulses in line 0.5 mm apart. If necessary, the laser pulses can be aimed at toric IOL axis 180° apart. The laser pulse marks the cornea with a small disruption, and blanching of the stroma remains visible for 48 hours or longer (Figure 2). The long-lasting mark is important for those rare cases in which revisional surgery for lens realignment becomes necessary during the days after lens implantation. The Sunalp YAG laser lens (patent pending) is a single-use acrylic lens that will be available in the near future.
Even though there are other methods for marking the corneal axis, these either require specialized and expensive equipment or are not as precise as marking with the Sunalp YAG laser lens.
- References:
- Cha D, et al. J Refract Surg. 2011;doi:10.3928/1081597X-20101005-01.
- de Bernardo M, et al. Eur J Ophthalmol. 2014;doi:10.5301/ejo.5000415.
- Fea AM, et al. Eye (Lond). 2006;doi:10.1038/sj.eye.6701994.
- Hoffer KJ. Am J Ophthalmol. 1980;doi:10.1016/S0002-9394(14)74917-7.
- Ianchulev T, et al. Ophthalmology. 2014;doi:10.1016/j.ophtha.2013.08.041.
- Popp N, et al. J Cataract Refract Surg. 2012;doi:10.1016/j.jcrs.2012.07.039.
- Zhang B, et al. Int J Ophthalmol. 2015;doi:10.3980/j.issn.2222-3959.2015.04.16.
- For more information:
- Murad A. Sunalp, MD, MBA, FACS, and Myhidin H. Shehu, MD, MBA, can be reached at Sunalp Laser Vision, 800 E. Merritt Ave., Suite 109, Tulare, CA 93274; email: slv@sunalplaservision.com and dini@sunalplaservision.com.
- Edited by Thomas “TJ” John, MD, a clinical associate professor at Loyola University at Chicago and in private practice in Oak Brook, Tinley Park and Oak Lawn, Ill. He can be reached at tjcornea@gmail.com.
Disclosures: Sunalp reports no relevant financial disclosures but reports that the Sunalp YAG laser lens is planned to be manufactured and sold in the future. Shehu and John report no relevant financial disclosures.