Ophthalmologists are on the brink of experiencing an upsurge in the number of patients with a phakic IOL who will require an explantation. Not only does myopia induce cataract, but the phakic lens itself also increases the chance of cataract formation. If a phakic IOL is implanted in an older patient, this may also affect the rate of cataract formation.
Simultaneous phakic IOL explantation and phacoemulsification makes the use of an IOL power calculation by standard ultrasound biometry particularly challenging. In eyes presenting with cataract that previously underwent bioptics (ie, phakic IOL plus corneal refractive surgery), this calculation is even more troublesome because we must account for the modification of corneal refractive power. Fortunately, there is a simple and reliable way to calculate IOL power in myopes without obtaining an axial length measurement or keratometry (K) reading.
INTRAOPERATIVE AUTOREFRACTION
Intraoperative autorefraction either checks the power of an IOL (pseudophakic technique)1 or calculates IOL power after the lens is emulsified (aphakic technique).2 In the aphakic technique, the nucleus is emulsified; the cortex is aspirated; and the aphakic spherical equivalent, which is converted into IOL power for emmetropia, is calculated with a handheld autorefractor (Nikon Retinomax 2; Nikon Corp., Tokyo).
The relationship between aphakic spherical equivalent (x) and IOL for emmetropia (y) is expressed by y = 0.07 x2 + 1.27 x + 1.22, which I have retrospectively calculated3 in a series of 82 eyes (Table 1). Intraoperative autorefraction does not account for the IOL's final position, making this calculation more accurate in myopic eyes in which a low-power IOL is implanted; it is not recommended in hyperopic eyes.
When explanting an anterior chamber phakic IOL, peribulbar anesthesia is recommended because it eases the pain associated with iris manipulation. Topical anesthesia is recommended for posterior chamber phakic IOL removal.
TECHNIQUE
First, create a limbal tunnel to remove the phakic IOL, keeping in mind that rigid IOLs may require an incision as large as 6 mm. Angle-supported phakic IOLs may induce angle synechiae, which must be delicately freed to avoid excess bleeding or iris dialysis.
After the phakic IOL is explanted, reduce the tunnel to the width of the phaco tip; we typically use two 10-0 nylon radial sutures. In some cases, posterior synechiae must be addressed, and an atonic iris may require disposable iris hooks for phacoemulsification (Figure 1).
Perform phacoemulsification, creating the capsulorrhexis and completing hydrodissection, nucleus ultrasound emulsification, and cortical aspiration. Next, reform the anterior chamber with balanced salt solution, and pull the microscope away from the eye. Wait a minimum a of 30 seconds to allow the patient to recover from the glare of the microscope light. Then, perform the autorefractometry (Figure 2). Before performing autorefraction, extreme hypotony or hypertony should be ruled out using a technique such as digital intraocular pressure evaluation. Then, it is safe to initiate the autorefraction. The patient should remain on the operating bed with the eyelid speculum still in place. Choose and implant the appropriate IOL.
In a recently published series, 19 eyes (15 patients) underwent combined phakic IOL explantation and phacoemulsification.4 The mean preoperative spherical equivalent was -16.27 D. The IOLs removed were angle-supported phakic IOLs in 13 eyes, iris-fixated phakic IOLs in two eyes, and posterior chamber phakic IOLs in four eyes. In six eyes, bioptics (ie, adjunctive photorefractive keratectomy [PRK]) was previously performed. The mean postoperative spherical equivalent was -0.56 D (SD 0.40; range, 0 to -1.50). Eleven eyes (58%) were within ±0.50 D of attempted refraction; 17 eyes (89%) were within ±1.00 D. No eye was more than 2.00 D from intended refraction.
CASE STUDY
Seven years ago, a 42-year-old woman with bilateral high myopia underwent bilateral implantation of rigid angle-supported phakic IOLs followed by PRK for astigmatic correction. No ultrasound biometry was performed, and all preoperative data were missing when she came to our facility. The patient had developed a grade 3+ nuclear cataract in her left eye, inducing -4.00 D of myopia. Her BCVA was 0.5.
I performed an intraoperative autorefraction, revealing an aphakic spherical equivalent of 2.00 D. I explanted the phakic IOL, performed phacoemulsification, and implanted a 4.00 D IOL (A-constant, 118.2) in the capsular bag. Postoperative refraction was plano; her UCVA was 0.9.
OTHER USES OF INTRAOPERATIVE AUTOREFRACTION
Intraoperative autorefraction is my favorite IOL calculation method for (1) cataract after corneal refractive surgery and (2) myopic refractive lens exchange. In the former, intraoperative autorefraction overcomes the difficulties of determining true corneal power after the corneal curvature has been modified. In the latter, this technique is more accurate than standard ultrasound biometry. In my last 55 consecutive cases of myopic lens exchange, final absolute mean spherical equivalent was 0.62 D (SD, 0.61). Only two refractive surprises occurred (ie, -2.00 D and -3.00 D residual error).
We also use intraoperative autorefraction when standard biometry provides an unexpected IOL power (eg, indicating a 28.00 D IOL in an emmetropic eye). In such cases, performing autorefraction before the patient leaves the operating bed may avoid later refractive surprises and/or the need for a second surgery. When the result is not between -2.00 D and 0.75 D, I exchange the IOL immediately. Verification of IOL power using intraoperative autorefraction is approximate (especially with high-powered IOLs) because the position of the IOL at the end of surgery is not definitive.
ALTERNATIVES
In some cases, intraoperative autorefraction is not the safest option, including (1) patients who squeeze their eyelids during surgery, which induces up to 5.00 D of with-the-rule astigmatism, (2) anxious patients who are unable to maintain fixation for a few seconds, (3) patients with decentered corneal refractive surgery, and (4) patients who have experienced intraoperative complications or vitreous pressure. If the corneal shape is not too altered, keratoconus is not an absolute contraindication.5
The main alternative to intraoperative autorefraction is partial coherence interferometry (IOLMaster; Carl Zeiss Meditec AG, Jena, Germany), providing reliable axial length measurements in eyes with phakic IOLs.6 Intraoperative ultrasound biometry, sometimes used for cataract surgery in silicone-filled eyes, is another option. This method is performed between silicone oil removal and cataract surgery.7
CONCLUSION
Intraoperative autorefraction is easy, inexpensive, and reliable in myopic eyes. It may solve difficult IOL power calculation situations, such as in eyes with a phakic IOL. Even after corneal refractive surgery, intraoperative autorefraction does not require an axial length measurement or K reading.
Antonio Leccisotti, MD, PhD, is a Visiting Professor at the School of Biomedical Sciences, University of Ulster, Coleraine, UK, and the Director of the Ophthalmic Department, Casa di Cura Rugani, Siena, Italy. Dr. Leccisotti states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +39 335 8118324; fax: +39 0577 578600; leccisotti@libero.it.
