Intraocular lens (IOL) power calculation in post-refractive surgery cases poses a unique surgical challenge because of the altered corneal curvature in flap-based corneal ablative procedures.1,2 Different formulas have been developed based on clinical historical data and various corrective factors; however, up to 45% of eyes might fall outside 0.5 diopter (D) of the intended target refraction despite using these formulas to calculate IOL power.3–6 A postoperative refractive surprise can occur, and a high magnitude of residual refractive error might necessitate an IOL exchange.
Intraocular lens power calculation in post-refractive surgery pseudophakia is difficult in the absence of preoperative records. The Optiwave Refractive Analysis System intraoperative wavefront aberrometer (Wavetec Vision Systems, Inc.) provides real-time on-table refractive measurements to guide decisions during cataract surgery. We describe a case of intraoperative aberrometry–assisted IOL power selection in a post-refractive surgery patient with an IOL surprise after phacoemulsification.
A 46-year-old woman presented with a suboptimal gain in vision in the right eye 1 week after cataract surgery. She developed diminution of vision in the right eye for 6 months and was diagnosed as having presenile cataract, for which she had phacoemulsification with posterior chamber IOL implantation (SRK II formula: +12.5 D) 1 week before presentation. The patient had a history of laser in situ keratomileusis (LASIK) in both eyes 17 years previously.
On examination, the uncorrected distance visual acuity (UDVA) was 20/300 in the right eye and 20/20 in the left eye. The corrected distance visual acuity (CDVA) in the right eye was 20/20 with refraction of +4.50 +1.00 × 170. The right eye had a well-centered single-piece foldable IOL in the bag, and the left eye was phakic with a clear lens. Optical biometry was performed using the IOLMaster 500 system (Carl Zeiss Meditec AG). The axial length was 27.63 mm in the right eye, 27.82 mm in the left eye, and keratometry was 36.93 @ 90/37.25 @ 180 and 36.29 @ 179/37.17 @ 89, respectively. The specular microscopy count was 3284 cells/mm2 in the right eye and 3456 cells/mm2 in the left eye.
An IOL exchange with intraoperative aberrometry–assisted IOL power selection was planned. Written informed consent was obtained from the patient, and the procedure adhered to the tenets of the Declaration of Helsinki. No preoperative historical data or lens thickness data were available, which precluded the use of established formulas such as Haigis L, Wang-Koch-Maloney, or clinical history method for post-refractive surgery IOL power calculation. The power in the right eye with various remaining formulas (SRK/T, Shammas, Barrett True K, and No History) ranged from +16.5 D to +19.5 D.
Intraoperatively, the IOL was cut with Vannas scissors and explanted through a 2.8 mm temporal clear corneal incision after the endothelium was coated and the bag filled with a dispersive ophthalmic viscosurgical device (Figure 1, A). Intraoperative aberrometry was used to perform the aphakic refractive analysis, and the power estimated by intraoperative aberrometry was +20.0 D (target residual refractive error −0.15 D) (Figure 1, B and C). A +20.0 D monofocal IOL (Acrysof IQ, Alcon Laboratories, Inc.) was implanted in the bag.
One day postoperatively, the UDVA was 20/20 with a manifest refraction of −0.50 +0.75 × 137. The IOL was well centered and stable (Figure 2, A and B). The specular microscopy count was 2750 cells/mm2.
Post-refractive surgery IOL power calculation is challenging, and multiple formulas have been described to improve the accuracy of IOL power calculation in such cases.1–5 However, most of these formulas were developed for phakic eyes and require the input of historical data or anterior chamber depth with lens thickness.3–5 No formulas have been devised for pseudophakic eyes, and IOL power calculation in cases with an IOL surprise might not be accurate in the absence of adequate preoperative data.
In our case, the history of LASIK was not elicited by the initial operating surgeon, which resulted in the selection of the wrong IOL formula (SRK II7) and a hyperopic refractive surprise. It is essential to specifically elicit a history of previous refractive surgery in all young myopic patients presenting with presenile cataract.
Intraoperative aberrometry is more accurate than conventional formulas in post-refractive surgery IOL power calculation.8 It does not rely on preoperative data, which can be inaccurate or unavailable in post-LASIK patients. To our knowledge, this is the first instance in which intraoperative aberrometry was successfully used for IOL power calculation in a case of IOL exchange in a post-refractive surgery patient with an IOL surprise.
None of the authors has a financial or proprietary interest in any material or method mentioned.
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. Accessed November 22, 2017