A 54-year-old man underwent uncomplicated cataract surgery with insertion of a Tecnis Multifocal IOL OS. He was very happy with his improved vision immediately following the surgery: on postop day one his uncorrected acuity was 20/25+2 at distance and J3 at near, but at week one his visual acuity was 20/50+2 and J3.
Mild punctate epitheliopathy of the central and inferior cornea was detected, and the patient was instructed to use non-preserved artificial tears qid. At the one-month postop visit he complained that his vision was still blurry and he was having difficulty with both distance and near vision.
On examination, his uncorrected vision was unchanged. With a manifest refraction of -1.25+0.50x60 his visual acuity improved to 20/20 and J1. An anterior segment exam showed a clear cornea with no punctate staining, a quiet anterior chamber, a well-centered multifocal IOL, and no posterior capsular opacity. The posterior segment exam was normal. The macula was flat with a sharp foveal reflex.
The patient had a myopic refractive surprise. What is the differential diagnosis for postop refractive surprise?
The differential diagnosis includes errors in preoperative measurements (i.e., axial length and/or keratometry, particularly in patients with previous corneal refractive surgery), very high or low axial length or keratometry values, use of improper IOL calculation formula, implantation of wrong power IOL, corneal pathology (i.e., edema, superficial punctate keratitis, anterior basement membrane dystrophy), cystoid macular edema (hyperopic shift), and displacement of the IOL due to capsular block (myopic shift), instability or capsular bag fibrosis.
Additional information: the patient did not have any prior corneal refractive procedures, his axial length and keratometry values were close to average and were consistent and reproducible on IOLMaster measurements, 3 IOL calculation formulas (Haigis, Holladay 2, and SRK/T) were in agreement, the correct IOL power was implanted, and there was no corneal or macular pathology present at the one month visit.
The patient was given a prescription for glasses by his optometrist and scheduled for a follow up exam 2 months later. At the subsequent visit, his vision and exam were unchanged except for trace folds in the posterior capsule. The patient did not want to wear glasses; therefore, he was told to return to his surgeon to discuss surgical correction with PRK/LASIK, IOL exchange, or piggyback IOL.
The surgeon attributed the residual refractive error to IOL movement from capsular contraction/fibrosis. This was discussed with the patient and a Nd:YAG laser posterior capsulotomy was recommended. On follow up exam one week after the laser procedure, the patient reported that his vision had improved. His uncorrected visual acuity was 20/20 and J1+. The manifest refraction was found to be -0.25+0.25x15.
Discussion: This case illustrates some important points:
- Subtle ocular abnormalities (i.e., tear film, SPK, ABMD, PCO, CME) can have a significant impact on visual acuity, especially in patients with multifocal lens implants. In this case, capsular changes caused the refractive surprise. Capsular contraction typically results in forward displacement of an IOL with a resulting myopic shift, as was seen in this patient. However, this typically does not present so quickly after surgery (except for anterior vaulting of a Crystalens), the shift often drifts over time as the capsule contracts and displaces the lens more, and usually some degree of capsular opacification is evident on slit lamp exam.
- Evaluation and management should occur in a step-wise fashion: 1) determine the etiology of the refractive error prior to performing any corrective procedure; 2) treat any tear film, corneal, and macular pathology first. Similarly, any posterior capsular fibrosis/opacification should be treated because even mild changes in the capsule can cause visual impairment, particularly with multifocal IOLs; 3) surgical correction can be explored if the refractive error persists and is stable.
- Remember that opening the posterior capsule during the early postoperative period after cataract surgery increases the risk of CME. Therefore, if a posterior capsulotomy is performed within 3 months of surgery, the surgeon should discuss the risk of CME with the patient and should consider prophylactic treatment with a topical NSAID and steroid.