ReviewA Review of Randomized Controlled Trials of Penetrating Keratoplasty Techniques
Section snippets
Uncontrolled Trials
When introducing a new technique, there is a tendency to select patients who will do well and to exclude those in whom the technique is not suitable or is likely to be difficult to perform. When analyzing the outcomes of a proposed new technique, attention inevitably will be drawn to those with a poor outcome. Patients who do badly may be excluded after subsequent enquiry reveals some sort of protocol violation, whereas attention will not be drawn to patients with a good outcome; thus, protocol
Historical Controls
Current surgical techniques may be compared with previous results of other techniques either from the same unit or from the scientific literature. This method has several disadvantages. There may have been different or unclear inclusion/exclusion criteria for historical controls; therefore, there may be systematic differences between groups other than the surgical techniques used. There also may have been temporal shifts in diagnostic criteria. Patients with different disease severities or with
Concurrent Nonrandomized Controls
Where controls are not randomized, the investigator or patient may know in advance which technique the patient will receive should they enter the trial. This may influence the investigator’s (or patient’s) decision regarding entry. Judgment by the investigator as to which treatment is received generally is considered to be unacceptable. There also may be different prognostic variables between groups (e.g., different surgeons or different institutions). Matching on more than a few factors is
Randomized Controlled Trials
Randomized controlled trials (RCTs) are essential tools for testing the efficacy of therapeutic interventions. Uncontrolled or poorly controlled studies may cause overestimation or underestimation of the effects of a new treatment, as compared with properly controlled trials.4 The advantage of a randomized trial is that cases with known or unknown prognostic biases are randomly (and, hopefully, evenly) distributed between the various arms of the study. Few RCTs existed before 1950.
The purpose
Literature Search
More than one database was searched. The search strategy is shown in Table 1. Pre-Medline publications were also searched back to 1964, and Index Medicus was hand searched back to 1945. Relevant articles from the bibliographies of existing trials also were checked. The review focused on surgical techniques for elective PK for visual reasons. It also included lamellar surgical techniques for deep stromal disease. Exclusion criteria were non-English language, animal studies, in vitro studies,
Results
Detailed observations about the studies are presented in Table 3.
Choice of Outcome Measures
In general, there is a tendency to choose ocular measurements as outcome variables rather than patient-centered outcome measures. Ocular measurements tend to be more responsive to interventions but have less meaning in terms of satisfaction and quality-of-life improvement for the patient. The issue of astigmatism provides a useful example. In Seitz et al’s study,10 the difference in outcome was greater for keratometric and topographic astigmatism than for refractive astigmatism; however,
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Manuscript no. 2004-48.