During the past 2 decades, the field of laser refractive surgery has witnessed dramatic advances introduced by new technologies.1 LASIK has become the most common elective operation, with more than 55 million procedures performed worldwide as of 2012 (2014 Market Scope data).

Several recent reports have provided evidence for a trend toward higher rates of myopia worldwide. Therefore, a greater understanding of both the cause and development of refractive error through basic, clinical, and epidemiologic studies is crucial in order to perfect existing treatments and begin to formulate preventive strategies.2

Many studies have analyzed the postoperative outcomes of refractive surgery, but only a few have focused on pre- and intraoperative biometric parameters, flap creation, and ablation nomograms. Controversies regarding the prevalence and impact of ocular residual astigmatism and the influence of age and sex on the efficacy of the laser treatment still exist. These conflicting results may be attributed to difficulties in analyzing and comparing findings among studies that typically include only small numbers of patients and sites and various excimer laser platforms and techniques for flap creation. Lack of standardization in patient assessment and selection leads to a high degree of bias and significant discrepancies in results.

In 2006, the Eye Clinic of the University Medical Center Hamburg Eppendorf and Care Vision initiated a clinical and scientific cooperation, which is the basis of the Hamburg Refractive Database. One strict protocol (last updated November 2014) was implemented at refractive clinics in Hamburg, Berlin, Hannover, Cologne, Frankfurt, Stuttgart, Nuremberg, Munich, and Vienna to regulate preoperative assessment, intraoperative setting, and postoperative regimen, with the ultimate goal of standardizing key perioperative parameters and minimizing potential bias.

In addition to general medical and ophthalmic histories, preoperative measurements include distance UCVA, distance BCVA, manifest refraction, cycloplegic refraction, tonometry, mesopic pupillometry (Colvard pupillometer), pachymetry, corneal topography (Orbscan; Bausch + Lomb and Pentacam; Oculus Optikgeräte), slit-lamp examination of the anterior segment, and fundoscopy. A total of 234 pre-, intra-, and postoperative parameters are automatically documented.3

With clinician users following these guidelines, the Hamburg Refractive Database delivers valuable information regarding the prevalence and distribution of refractive error, especially the intraindividual distribution, and helps ensure that clinical decision-making is data-driven.

STUDY POPULATION

The Hamburg Refractive Database is continually expanded and updated. Today, our databank contains 71,098 patients (142,195 eyes) who attended refractive clinics in Germany and Austria between April 2006 and November 2014 for the treatment of ametropias. Most of these patients were candidates for excimer laser
refractive surgery, either LASIK or PRK. Those whose refractive errors exceeded the treatment range for laser vision correction were candidates for phakic IOL implantation or clear lens extraction.

Patients were excluded from the study for any of the following diagnoses: history of ocular surgery, including cataract or refractive surgery; ptosis; clinically significant retinal pathology; glaucoma; and optic neuropathy. The study protocol was conducted according to the tenets of the World Medical Association’s Declaration of Helsinki regarding scientific research on human patients. Informed consent was obtained from the patients after explanation of the nature and possible consequences of the study. The analysis of the data was approved by the local ethics committee.

STATISTICAL ANALYSIS

After data were compiled, they were entered into a spreadsheet program (Excel; Hamburg Refractive Database) and further statistically analyzed with SPSS software (version 15.0).

A study was initiated recently to determine the amount of topographic astigmatism (also termed ocular residual astigmatism, or ORA) in eyes that have no refractive cylinder. This study included 267 eyes of 267 consecutive myopic patients with refractive plano cylinder whose data were entered into the Hamburg Refractive Database. Receiver operating characteristic analysis was used to find the cutoff values of preoperative ORA that can best discriminate between groups of efficacy and safety indices in preoperative plano refractive cylinder eyes. A significantly greater efficacy index was achieved in eyes with low preoperative ORA. Bivariate ordinary least squares regression showed that there was a statistically significant negative correlation between preoperative ORA magnitude and efficacy index. Each diopter of preoperative ORA reduced efficacy by 0.07. Results of this study were also presented at the 19th ESCRS Winter Meeting in Istanbul.
OUTLOOK

Studies derived from the Hamburg Refractive Database3,4 to date have revealed valuable normative parameters and their correlations in the largest cohort of Central European refractive surgery candidates. Based on these results, we have initiated further studies to explore the impact of preoperative parameters on the postoperative safety, efficacy, predictability, and refractive stability of laser vision correction and to transfer the obtained normative parameters to better define cutoff values between normal and diseased corneas, as in keratoconus. n

1. Reinstein DZ, Archer TJ, Gobbe M. The history of LASIK. J Refract Surg. 2012;28(4):291-298.

2. Bloom RI, Friedman IB, Chuck RS. Increasing rates of myopia: the long view. Curr Opin Ophthalmol. 2010;21(4):247-248.

3. Linke SJ, Richard G, Katz T. Prevalence and associations of anisometropia with spherical ametropia, cylindrical power, age, and sex in refractive surgery candidates. Invest Ophthalmol Vis Sci. 2011;52(10):7538-7547.

4. Linke SJ, Baviera J, Munzer G, Steinberg J, Richard G, Katz T. Association between ocular dominance and spherical/astigmatic anisometropia, age, and sex: analysis of 10,264 myopic individuals. Invest Ophthalmol Vis Sci. 2011;52(12):9166-9173.