To the Editor:
In the so-called bioptics approach, a secondary excimer laser procedure is performed for residual ametropia after primary intraocular lens (IOL) implantation.1 Recently, three patients presented who developed a hyperopic defect following LASIK for residual ametropia after cataract surgery with a refractive multifocal IOL. Subjective refraction before LASIK ranged between −1.00 and −1.50 diopters (D), with corrected distance visual acuity (CDVA) ranging between 20/32 and 20/25. After uneventful myopic LASIK in one eye of each patient, all three eyes presented a hyperopic outcome of +2.50 D with CDVA of 20/20 in every case. Retrospective examinations of ablation reports in all three eyes excluded any possible source of error.
A likely explanation for the hyperopic surprise found in these patients is presented herein: subjective refraction for CDVA was obtained using the near focus of the multifocal IOL, therefore, the eyes were not myopic of −1.00 to −1.50 D, but hyperopic of +1.00 to +1.50 D. Hence, the myopic ablation resulted in a more hyperopic residual defect.
Distance vision in an eye implanted with a multifocal IOL can be corrected by using either of the two principal foci of the IOL, but only if the far focus is in-focus for far vision, will the near focus be useful for near vision. The Figure shows the typical defocus curve of a refractive multifocal IOL. Given an eye with an actual residual hyperopia of +1.00 D after refractive multifocal IOL implantation, CDVA can be obtained using the real ametropia of +1.00 D (point A in the Figure: far focus in-focus for far and near focus in-focus for near) or −1.25 D (point B in the Figure: far focus out-of-focus for far and near focus in-focus for far and out-of-focus for near). Before any secondary intervention, it is necessary to confirm that the far focus of the multifocal IOL is being used for distance subjective refraction. This can be done by any of the following tests:
- Once CDVA has been determined, distance-corrected near visual acuity should be measured and it should be similar or slightly inferior to CDVA, depending on the multifocal IOL model.
- A +2.25- or +2.50-D lens should be placed on top of the refraction for CDVA, and far vision should be measured again to show a dramatic decrease.
- A −2.25- or −2.50-D lens should be placed on top of the refraction for CDVA, and far vision should be measured again to show a slight decrease, because the near focus of the IOL is being used for distance vision.
Figure. Defocus curve of a refractive bifocal intraocular lens (IOL). “A” represents the vision through the far focus of the IOL and “B” represents the vision through the near focus of the lens. Errors result when the far refraction is obtained through the near focus (B).
Unexpected outcomes in any of the three tests indicate the possibility of having used the near focus of the refractive multifocal IOL for far vision, leading to a false diagnosis of myopia in an eye that actually presents with low hyperopia.
Pseudomyopia in eyes with multifocal refractive IOLs has been reported using automatic refraction, and therefore, autorefractometers are not helpful in this situation.2,3 Careful subjective refraction before LASIK enhancement in bioptics using refractive multifocal IOLs is mandatory.
César Albarrán-Diego, PhD
Gonzalo Muñoz, PhD, FEBO
Teresa Ferrer-Blasco, PhD
- Zaldivar R, Davidorf JM, Oscherow S, Ricur G, Piezzi V. Combined posterior chamber phakic intraocular lens and laser in situ keratomileusis: bioptics for extreme myopia. J Refract Surg. 1999;15(3):299–308.
- Muñoz G, Albarrán-Diego C, Sakla HF. Validity of autorefraction after cataract surgery with multifocal ReZoom intraocular lens implantation. J Cataract Refract Surg. 2007;33(9):1573–1578. doi:10.1016/j.jcrs.2007.05.024 [CrossRef]
- Muñoz G, Albarrán-Diego C, Sakla HF. Autorefraction after multifocal IOLs. Ophthalmology. 2007;114(11):2100. doi:10.1016/j.ophtha.2007.05.049 [CrossRef]