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Cataract Surgery | Jul 2015

Managing Residual Refractive Errors and Postoperative Astigmatism

Proper understanding of the patient's expectations and accurate measurement of residual refractive error are key.

Many cataract patients today expect emmetropia and spectacle independence postoperatively. In order to meet these expectations, an understanding of residual refractive errors and their management is increasingly important.

Residual refractive errors can be related to a variety of factors. There may be errors in the preoperative assessments of axial length and corneal power, an unknown history of prior refractive surgery, incorrect IOL placement or positioning, or residual regular or irregular corneal astigmatism. Decreased visual acuity may also result from ocular surface pathology, posterior capsular opacity, and macular or optic nerve pathology. Not meeting patient expectations can make even small residual errors appear to be large ones.

ASSESSING THE ERROR

First and foremost, it is important to listen to the patient to understand the exact nature of his or her complaints. Does he or she desire improved distance vision, near vision, or both? Is he or she amenable to spectacles or contact lenses, or is further surgery required to achieve satisfaction?

Proper assessment allows accurate patient counseling on procedural options and helps set appropriate expectations. Good ocular surface health is necessary to optimize postoperative results; conditions such as blepharitis and dry eye must be cleared up and the refraction must be stable prior to planning further surgery. Additionally, the surgeon must accurately assess the spherical and astigmatic refractive error and differentiate between regular and irregular astigmatism. Conveying to the patient that enhancements are occasionally necessary is an important part of both pre- and postoperative counseling.

CASE PRESENTATIONS: WHEN TO ENHANCE

The decision of when to enhance is not related to a particular visual acuity. Enhancement becomes relevant when the patient is unhappy with his or her postoperative outcome. Options for enhancement include spectacles, limbal relaxing incisions (LRIs), laser vision correction, IOL exchange, and piggyback IOL placement. The following five case presentations illustrate when to utilize these options.

Patient No. 1. A 65-year-old man underwent uncomplicated phacoemulsification in his left eye. At 1 month postoperative, his UCVA was 20/50 OS. BCVA was 20/20 with a manifest refraction of -1.00 +1.50 X 85º.

This case illustrates decreased visual acuity from residual astigmatism despite a spherical equivalent near plano. Therefore, Patient No. 1 could be managed with paired LRI incisions on the steep corneal axis. Because of the coupling effect, LRIs can reduce astigmatism without changing the spherical power. This patient’s spherical equivalent was -0.25 D, making him a good candidate for this procedure. LRIs are relatively easy to perform, fairly inexpensive for the patient, and can be done in a minor operating room or at the slit lamp. Several LRI nomograms are available, including those by Louis D. “Skip” Nichamin, MD; Eric D. Donnenfeld, MD; and Douglas D. Koch, MD. The procedure can be performed with a diamond blade or femtosecond laser. Generally, the depth of the incision is 600 μm, depending on the patient’s pachymetry. It is important to remember that these procedures specifically treat postoperative refractive cylinder, not corneal astigmatism alone. This patient required paired LRIs with 40° of arc at the 85° axis to treat the refractive cylinder.

Patient No. 2. A 63-year-old pilot underwent cataract extraction and IOL implantation in both eyes. A monofocal implant was placed in each eye, and postoperative UCVA was 20/40 OD and 20/20 OS. A manifest refraction OD of -1.50 +1.25 X 80º yielded 20/20 BCVA; however, the patient was not interested in spectacle correction. Therefore, it was determined that the residual myopic astigmatism would best be corrected with laser vision correction. LASIK or PRK can be used in conjunction with toric and nontoric monofocal IOLs but should be used selectively in patients with multifocal IOLs.1

Because Patient No. 2 had a myopic spherical equivalent, he would not have been fully corrected by astigmatic keratotomy alone. An excimer laser procedure can treat both residual astigmatism and myopia, and this is currently one of the most accurate methods of refractive enhancement.2 Although LASIK leads to faster visual recovery and minimal discomfort, the procedure carries the potential for flap-related complications. PRK does not require a flap and leads to fewer basement membrane issues than LASIK; however, visual recovery is slower, and the procedure is associated with more pain and the risk of transient corneal haze. After a PRK enhancement, this patient was happy and 20/20 by about 3 months postoperatively.

Patient No. 3. A 60-year-old woman presented with a history of LASIK for myopia. She did not have access to any of her old medical records and had visually significant cataracts in both eyes. UCVA was 20/50 OD and 20/60 OS. The patient’s corneas were clear, with LASIK flaps noted in both eyes. Also in both eyes, the lenses had 2+ nuclear sclerosis, 2+ cortical spokes, and 1 to 2+ posterior subcapsular cataract changes. The remainder of the exam was normal.

Cataract extraction with IOL placement OD was uneventful; however, the postoperative UCVA in Patient No. 3 was 20/60 at 1 and 2 months postoperative. With 2.00 D of sphere, BCVA was 20/20. The small degree of hyperopic refractive error without astigmatism made her an ideal candidate for piggyback IOL implantation. Considerations for this procedure include adequate anterior chamber depth, healthy endothelium, a stable refraction, and minimal astigmatism. Contraindications include pigment dispersion syndrome, zonular weakness, pseudoexfoliation, presence of a capsular tension ring (CTR), low endothelial cell count, and significant astigmatism (although toric piggyback IOLs are available outside the United States).

Piggyback IOLs are usually of low power (-4.00 to 4.00 D). Two commonly used lenses have been the Clariflex (Abbott Medical Optics) and the STAAR AQ5010 (STAAR Surgical), although the former is no longer available. The STAAR AQ5010 is a three-piece silicone IOL with a thin profile and a 6.3-mm optic. It has a 14-mm overall diameter with 10° of posterior angulation to keep the lens optic away from the posterior iris. Silicone lenses avoid interlenticular opacity with a bag-fixated acrylic IOL.

The piggyback IOL’s power is entirely dependent on the pseudophakic manifest refraction. The spherical equivalent of the manifest refraction and the A-constant of the piggyback IOL are all that is necessary for power calculation. For patients with postoperative hyperopic refractive error, the spherical equivalent should be multiplied by 1.5 to find the proper piggyback IOL power. For patients with postoperative myopic refractive error, the spherical equivalent should be multiplied by 1.2 to find the proper lens power. IOL power calculations can also be made using the Holladay R formula, the Gills nomogram, or the refractive vergence formula from Warren E. Hill, MD. Because the postoperative manifest refraction in this case was 2.00 D of sphere, the patient required a 3.00 D STAAR AQ5010V piggyback IOL.

The surgical technique for inserting a piggyback IOL is similar to that for primary IOL implantation. A cohesive OVD is used to distend the ciliary space. At this point, the entire lens can be placed in the anterior chamber, or the leading haptic can be placed into the ciliary sulcus. The trailing haptic is then inserted into the eye and tucked under the iris using a hook. Positioning the piggyback IOL in the sulcus should create separation between the piggyback IOL and the IOL in the capsular bag. There should also be a slight separation between the anterior piggyback IOL and the posterior iris. Once the new IOL is in the appropriate position, the OVD is removed from the eye and corneal incisions are closed with either stromal hydration or sutures. The learning curve is short for most surgeons because the steps required to place a piggyback IOL are similar to the steps used in most cataract and anterior segment surgeries.3

Patient No. 4. A 72-year-old woman reported decreased vision in her left eye for 6 to 9 months. Her BCVA OS was 20/60 with manifest refraction of -6.25 +1.75 X 32º. Her exam was consistent with decreased vision from cataract. A standard surgical plan was created with biometry and IOLMaster (Carl Zeiss Meditec) calculations. The axial length of her left eye was 25.62 mm. The IOLMaster keratometry (K) reading was 42.67 X 45.00 at 120° - ∆K = 2.23, which was similar to the Orbscan (Bausch + Lomb) K reading of 43.1 X 45.3 at 122° - ∆K = 2.2. A Tecnis Toric ZCT400 one-piece lens (Abbott Medical Optics) was calculated to be oriented at 115°, with anticipated residual cylinder of 0.04 D at 115°. Surgery was uneventful, and a 17.00 D Tecnis Toric lens was placed at 115°. The target refraction for this patient was -1.60 D.

On postoperative day 1, Patient No. 4 achieved a near UCVA of J3; however, she complained of double images and ghosting. These symptoms could be caused by ocular surface irregularity, induced astigmatism related to wound healing, IOL decentration or tilt, axis alignment error, or an error in IOL power calculation. After 10 days, the patient’s near UCVA was the same. On slit-lamp exam, the IOL appeared to be oriented at 160° instead of the intended 115°. Although estimation of the postoperative toric IOL axis can be difficult, a slightly more precise measurement can be made at the slit lamp using the iHandy Level (iHandy; https://itunes.apple.com/us/app/ihandy-level-free/id299852753?mt=8) or Axis Assistant (designed by José Miguel Varas, MD, and coded by Evandro Souza; https://itunes.apple.com/us/app/axis-assistant/id843536178?mt=8) smartphone apps. With these apps, the rotated slit beam is first oriented with the axis of the toric IOL. Then, the axis of the virtual level is oriented with axis of the rotated slit beam, at which point freezing the level in the app will measure the exact axis.

At a Glance

• Factors contributing to residual refractive errors can include errors in the assessment of axial length and corneal power, an unknown history of prior refractive surgery, incorrect IOL placement or positioning, and residual regular or irregular corneal astigmatism.
• Proper assessment allows accurate patient counseling on the procedural options and helps set appropriate expectations.
• Spectacles, LRIs, LASIK or PRK, IOL exchange, or piggyback IOL implantation are all management options at the surgeon’s disposal for solving postoperative refractive issues.

In this scenario, a secondary surgery for IOL rotation should be considered if the poor postoperative vision is secondary to the IOL being off-axis. Higher toric corrections have a larger impact on visual outcome; a 10° error in placement can lead to a 33% loss of effectiveness in the final outcome.4 It is also important to ensure that there is no significant spherical equivalent error. If error in the spherical equivalent is the true cause of the postoperative refractive error, then rotating the IOL may not fully alleviate the patient’s visual complaints. Surgical planning for IOL rotation can be enhanced by using the Astigmatism Fix calculator (www.astigmatismfix.com) developed by John P. Berdahl, MD, and David R. Hardten, MD, FACS. Lastly, posterior capsule and zonular integrity is essential to successfully rotating an IOL.

IOL rotation is best done at 2 to 4 weeks postoperative when refraction and measurements are stable. In the operating room, the surgeon marks the intended axis, reinflates the bag with cohesive OVD, and rotates the IOL until the lens is close to the intended orientation. If intraoperative aberrometry is available, this can be used to check for residual cylinder once the IOL has been rotated. The OVD is carefully removed from around the IOL, and the orientation of the IOL is confirmed once more. The IOL can be left in the capsular bag, or reverse optic capture can be used to stabilize the IOL with or without the use of a CTR.

In this case, IOL rotation was performed 2 weeks postoperatively with the placement of a CTR. On postoperative day 1, near UCVA in Patient No. 4 was J1+ without ghosting. The IOL was oriented at 118°, and refraction detected minimal residual cylinder. After 2 weeks, her near UCVA was J1 with stable orientation of the IOL.

Patient No. 5. A 67-year-old engineer with recent multifocal IOL placement in both eyes presented with distance UCVA of 20/25 and near UCVA of J1 in both eyes. He complained of halos, glare, and trouble reading in low light. He was unhappy with his overall quality of vision, which was not improved after a trial in spectacles. Topography measurements and endothelial cell counts appeared normal. The patient wondered if an Nd:YAG laser procedure might help him. The best option for an unhappy patient after uncomplicated cataract surgery with a normal corneal endothelium, normal topography, and good distance and near refractive outcome may simply be an IOL exchange. For Patient No. 5, an uncomplicated IOL exchange did resolve the visual aberrations.

IOL exchange is useful if there is an error in the spherical or cylindrical goal or if the patient is unhappy with the quality of his or her vision, including glare and visual aberrations. If the exchange is planned early in the postoperative course and the bag is intact, an IOL exchange with placement of the new IOL in the bag is an option. If the exchange is planned late in the postoperative course and the posterior capsule is open, an exchange can be done with placement of the new IOL in the sulcus. The need for anterior vitrectomy in this setting is significant.

Considerations for IOL exchange include the type and placement of the initial lens implant, the endothelial cell count, and the presence of persistent inflammation. The need for microsurgical scissors and forceps, an anterior vitrectomy, use of suture fixation, and CTRs or capsular tension segments should be anticipated. Peribulbar local anesthesia should be considered, as the case may require extensive manipulation. During the procedure, OVD is injected between the capsule and the existing IOL, as this allows gentle rotation and prolapse of the IOL out of the bag. The old IOL is cut or folded to remove it from the anterior chamber, and the new IOL is placed in the sulcus or the bag depending upon capsular integrity.

CONCLUSION

The key to managing residual postoperative refractive error is listening to the patient, understanding his or her expectations, and accurately measuring the residual refractive error. Ensure that the refractive error has stabilized before performing further surgery. Also, always take corneal regularity, IOP, and macular health into account prior to surgery or subsequent intervention. Once the problem has been defined, spectacles, LRIs, LASIK or PRK, IOL exchange, or piggyback IOL implantation are all management options at the surgeon’s disposal for solving postoperative refractive issues. n

1. Piñero DR, Ayala Espinosa MF, Alió JL. LASIK outcomes following multifocal and monofocal intraocular lens implantation. J Refract Surg. 2010; 26(8):569-577.

2. Alio JL, Abdelghany AA, Fernandez-Buenaga R. Management of residual refractive error after cataract surgery. Curr Opin Ophthalmol. 2014;25(4):291-297.

3. Rubenstein JB. Piggyback IOLs for residual refractive error after cataract surgery. Cataract &Refractive Surgery Today. 2012;28-30.

4. Roach L. Toric IOLs: four options for addressing residual astigmatism. Eyenet. 2012;29-31.

Jill S. Zaveri, MD
• Ophthalmology Resident, Rush University Medical Center, Chicago
jill_s_zaveri@rush.edu
• Financial disclosure: None

Jonathan B. Rubenstein, MD
• Vice Chairman and Deutsch Family Professor of Ophthalmology, Rush University Medical Center, Chicago
jonathan_rubenstein@rush.edu
• Financial disclosure: None

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