Accuracy of the Galilei Analyzer to Calculate the Effective Corneal Power After Corneal Refractive Surgery

The accuracy of IOL calculation is important for the visual outcome of patients undergoing
cataract extraction and IOL implantation. Different formulas such as Holladay I, HofferQ,
SRKT have been used with excellent results. All formulas use the corneal power among other
factors to calculate the IOL power. Corneal refractive surgery i.e. radial keratotomy (RK),
photorefractive keratectomy (PRK), and Laser in situ keratomileusis (LASIK) changes the
corneal power; therefore, it is difficult to measure the true corneal power after surgery by
any form of direct measurement, such as keratometry, or corneal topography. Keratometry and
topography assume a normal relationship between the anterior and posterior corneal
curvatures, and measure the anterior corneal radius. RK for myopia flattens both the anterior
corneal radius and the posterior corneal radius while PRK and LASIK for myopia flattens the
anterior corneal radius but leaves the posterior corneal radius mostly unchanged.

Standard keratometry measures an intermediate area and extrapolates the central power based
on some very broad assumptions. For this reason, keratometry, autokeratometry and simulated
keratometry by topography will typically over-estimate central corneal power following
keratorefractive surgery for myopia. This inaccuracy leads to an inability to meet the
patients' rising expectations and with the increasing popularity of refractive surgery,
calculating intraocular lens (IOL) power after refractive surgery is becoming increasingly
important.

Different methods to calculate the effective corneal power (keratometry) after refractive
surgery have been described (historical data, effective refractive power, modified Maloney
method, etc), however, intraocular lens power calculations in eyes with previous refractive
surgery remains difficult because of the inaccuracy of keratometry power measurements.

The Galilei dual Scheimpflug analyzer is a non-invasive, diagnostic system that combines dual
rotating Scheimpflug camera measurements and Placido optical system for corneal topography
and 3D analysis of the anterior eye segment. It provides pachymetry as well as elevation and
curvature mapping of the cornea. Additionally, the Ray tracing system delivers a more
accurate total corneal power and anterior chamber depth. The total corneal power that the
Galilei provides is an alternative that seems to be more accurate to calculate the IOL power
in patients who have undergone keratorefractive surgery prior to cataract extraction and IOL
implantation.

The purpose of this study is to determine the accuracy of the Galilei to calculate the
effective corneal power (keratometry, corneal curvature) in patients who have undergone both
corneal refractive surgery and lens extraction with intraocular lens implantation.

Inclusion Criteria:

- Subjects MUST fulfill the following conditions to qualify for enrollment into the
trial:

- Subject must have undergone corneal refractive surgery (RK, PRK or LASIK) prior
to cataract extraction.

- Age: 40 to 80 years old.

- Subjects must have undergone cataract extraction at least 4 weeks prior to
enrollment in this trial.

- Willing and able to comply with scheduled visits and other study procedures.

Exclusion Criteria:

Subjects with ANY of the following conditions on the eligibility exam may NOT be enrolled
into the trial.

Preoperative ocular pathology: amblyopia, rubella cataract, proliferative diabetic
retinopathy, shallow anterior chamber, macular edema, retinal detachment, aniridia or iris
atrophy, uveitis, history of iritis, iris neovascularization, medically uncontrolled
glaucoma, microphtalmus or macrophtalmus, optic nerve atrophy, macular degeneration (with
anticipated best postoperative visual acuity less than 20/30), advanced glaucomatous
damage, etc.

Uncontrolled diabetes. Use of any systemic or topical drug known to interfere with visual
performance. Contact lens use during the active treatment portion of the trial. Any
concurrent infectious/non infectious conjunctivitis, keratitis or uveitis. Any clinically
significant, serious or severe medical or psychiatric condition that may increase the risk
associated with study participation or study device implantation or may interfere with the
interpretation of study results.

Participation in (or current participation) any investigational drug or device trial within
the previous 30 days prior to the start date of this trial.

Intraocular conventional surgery (other than cataract extraction) within the past three
months or intraocular laser surgery within one month in the operated eye.