Surgery post LASIK and contrast sensitivity

Hiroko Bissen-Miyajima MD

Patients who have previously undergone LASIK for myopia are now undergoing cataract surgery in increasing numbers. These are patients who are accustomed to high quality, spectacle-free vision and are very likely to request implantation of a multifocal intraocular lens. It is therefore important for surgeons to be informed of the possible effects of myopic LASIK on the outcome of surgery, particularly in cases in which a premium intraocular lens (IOL) will be used.

“We sought to evaluate the impact of previous myopic LASIK on contrast sensitivity in patients who received diffractive multifocal IOLs at a single institution after myopic LASIK,” said Hiroko Bissen-Miyajima MD, PhD, Tokyo, Japan, to delegates at the XXXIII Congress of the ESCRS in Barcelona, Spain.

“Besides the well-known difficulty of IOL power calculation in post-LASIK eyes, contrast sensitivity is an important concern in these patients. This is not something that has been evaluated in previous publications of multifocal IOLs in eyes with previous LASIK, despite its importance to outcomes and patient satisfaction,” said Dr Bissen-Miyajima, Tokyo Dental College Suidobashi Hospital.

Discussing the results of a retrospective case series of 18 patients who had received either a ZMA00 or a ZMB00 (AMO) diffractive multifocal IOL between 2011 and 2014, Dr Bissen-Miyajima noted that all patients had received their LASIK at other surgical centres between 1999 and 2011. 

Relevant pre-phaco data included an average ocular axial length of 27.0mm; a mean central corneal thickness of 465μm; pre-op corneal refraction of 38 +/- 1.5D; and an average IOL power calculation of 20.0D. Also of note was the young age of patients undergoing cataract extraction, with a mean age of 48 +/- 10 years. 

MULTIVARIABLE REGRESSION ANALYSIS

Measurements performed at one month postoperatively included corneal higher-order aberration (HOA) and contrast sensitivity, with a calculation of the area under long contrast sensitivity (AULCSF). Using multivariable regression analysis, degradation in contrast sensitivity was assessed in relation to keratometry, corneal eccentricity, ocular axial length, central corneal thickness, HOA, corrected distance and near visual acuities, manifest refraction and patient age.

The results showed that AULCSF and contrast sensitivity were significantly decreased in eyes with a thinner central corneal thickness (P<0.05). This decrease was present at three and 12 cycles per degree (CPD, a measure of contrast sensitivity), although it was absent at 18CPD. 

“Thinner central corneas were the most significant ocular factor associated with decreased contrast sensitivity,” said Dr Bissen-Miyajima, who urged delegates to take this into account when planning on implanting a multifocal IOL in a post-LASIK eye. 

Hiroko Bissen-Miyajima: bissen@tdc.ac.jp