The authors have no financial interest. Unintended Myopic Biometric Error in a Posterior Amorphous Corneal Dystrophy Patient Submitted to Anterior Segment Scheimpflug Analysis The authors have no financial interest.

Abstract One case of post-phacoemulsification refractive surprise in a posterior amorphous corneal dystrophy patient is reported herein. The refractive error´s likely causative factor, as well as our approach once it was detected are discussed in this report.

Introduction Postoperative refractive prediction is an absolutely relevant issue for the cataract surgeon1. According to an ASCRS members´ survey in 2003, inappropriate lens power selection was the most common reason for IOL explantation or exchange2. We present a case of refractive surprise for a patient with posterior amorphous corneal dystrophy (PACD) and cataract submitted to phacoemulsification and bifocal intraocular lens (IOL) implantation.

Case Report On a routine consultation, a 63-year-old female patient complained of slowly progressive blurred vision and also some perception of haloes and glare for both eyes. Manifest refraction: OD +3.00 Sph – 0.50 Cyl @ 80º (20/40) OS +3.00 Sph – 0.50 Cyl @ 105º (20/30) At slitlamp examination, both eyes showed increased mid-stromal corneal refringency, narrow anterior chamber angle and a slight-to-moderate nuclear sclerosis. No other abnormalities were detected. Cataract and PACD were diagnosed.

Case Report Scheimpflug (Pentacam/Oculus) readings: OD OS

Case Report Axial length was measured by immersion biometry (Ocuscan/Alcon). IOL power was calculated using the SRK/T biometric formula for both eyes (bifocal ReSTOR SN6AD3 IOL/Alcon). She had an uneventful procedure for her OD. But on the 7th postoperative day, the patient was unhappy with her near and distance uncorrected vision. No abnormalities were detected at biomicroscopy. Scheimpflug topographic anterior segment analysis and all biometric calculations were carefully rechecked – and confirmed. An apparently irrelevant detail gave us a starting point to our investigation: the central keratometric readings obtained from the computerized keratometer (Humphrey) were nearly 1.00 diopter steeper than those ones from Scheimpflug. This new data input, yields an IOL power calculation nearly 1.00 diopter weaker then that IOL power previously selected.

Case Report To further investigate the case, we decided to use another technology, in an attempt to assess the actual anterior corneal curvature for both eyes. We performed corneal topography based on Placido´s discs reflection (OrbscanII /Bausch&Lomb).

Case Report For the OS, IOL power was recalculated using the effective central corneal power obtained from Placido´s discs. The IOL power was then “reset” at + 24.00 diopters, 2.00 diopters weaker in comparison to the power predicted by the Scheimpflug keratometric readings. The patient had an uneventful surgery for her OS. On the 7th postoperative day, the patient was happy with her near and distance uncorrected vision (20/25 – J1 at 40 cm). The undesired myopic refraction for the OD was addressed by photorefractive keratectomy enhancement, a month later.

Discussion There is no documented explanation for such inaccurate measurements in patients with PACD by the Scheimpflug system. To our knowledge, this is the first documented case in literature describing a central corneal curvature misreading by the Scheimpflug system in a patient with PACD. In this case, keratometric measurements obtained from the Scheimpflug system lead to postoperative refractive surprise, due to a flatter “measured central corneal” power than the “actual” one. We theorize that the abnormal corneal transparency may have disrupted the Scheimpflug system from functioning properly, inducing an artifactual central corneal applanation leading to inaccurate IOL selection among for our patient. Keratometric readings from computerized keratometer and also, from Placido´s discs are not influenced by the diminished PACD´s corneal transparancy – they rely essentially on corneal reflection.

Conclusions Among PACD patients - and possibly with any other diffuse corneal opacities - Scheimpflug readings, must be used with caution for IOL power calculations1; Postoperative refraction of the first operated eye offers a valuable tool, in terms of refractive prediction for the fellow eye, in accordance to the current literature3.

References Freitas G O, Carvalho M J. Post-Phacoemulsification Refractive Surprise in a Posterior Amorphous Corneal Dystrophy Patient: Report of one Case. Under Publication Process in Rev Bras Oftalmol. Narvaés J, Zimmerman G, Stulting R D, Chang D H. Accuracy of IOL power prediction using the Hoffer Q, Holladay I, Holladay II and SRK/T formulas. J Cataract Refract Surg 2006; 32:2050-2053. Covert D J, Henry C, Koenig S. IOL power selection in the second eye of patients undergoing bilateral, sequential cataract extraction. Ophthalmology 2010; 117:49-54.

Credits . Giuliano Freitas, M.D. giuliano@isoolhos.com.br Author. . Mário Carvalho, M.D. mario@isoolhos.com.br Co-author, surgeon. . Priscila Lopo, M.D. priscila@isoolhos.com.br Co-author. ISO OLHOS – Instituto de Saúde Ocular Uberlandia – MG - Brazil www.isoolhos.com.br