What's in a name: keratoconus, pellucid marginal degeneration, and related thinning disorders

PURPOSE

To discuss the implications of the current nomenclature and use of current diagnostic modalities on the classification and treatment of pellucid marginal degeneration and keratoconus.

DESIGN

Perspective analysis of the literature.

METHODS

Analysis of published reports on the various treatment methods for pellucid marginal degeneration and keratoconus, and the technologies used in these studies to support the diagnosis and classification of these ectatic disorders.

RESULTS

Many studies exploring the different treatment modalities for pellucid marginal degeneration and keratoconus rely mainly on anterior curvature maps to establish the diagnosis of these ectatic disorders, and either do not utilize or disregard information provided by pachymetric maps and posterior elevation maps. In addition, the interchangeability of the nomenclature used to describe these disorders in the literature makes it even more difficult for the clinician to determine the applicability of the results to their patient population.

CONCLUSIONS

We propose that future studies minimally include anterior and posterior elevation maps, anterior curvature topography, and full pachymetric maps. This will allow practitioners a better understanding of the study population, and allow them to ascertain when and in whom the treatment modality being explored may be applicable.

Long-term stability of the posterior cornea after laser in situ keratomileusis

PURPOSE

To study long-term changes in posterior corneal elevation after laser in situ keratomileusis (LASIK) using Scheimpflug topography (Pentacam, Oculus, Inc.) in eyes 1 year after LASIK.

SETTING

Department of Ophthalmology, Albany Medical Center, and a private practice, Albany, New York, USA.

METHODS

One hundred two myopic eyes of 52 consecutive patients presenting for their 1-year follow-up were prospectively evaluated using the Pentacam to determine elevation changes to the posterior corneal surface between preoperative and 1-year postoperative measurements. Changes in posterior elevation were performed by comparing the best-fit sphere preoperatively and postoperatively with a fixed reference sphere determined by the central 9.0 mm preoperative cornea. Statistical and graphical analyses were performed.

RESULTS

One hundred two post-LASIK eyes (mean correction -4.33 diopters; mean ablation depth 68.70 microm; mean estimated residual bed thickness 327 microm) had a mean posterior displacement of -0.47 microm +/- 3.48 (SD) (range -10.0 to +7 microm). The mean follow-up period was 13.6 months (range 8.8 to 19.3 months).

CONCLUSIONS

In this population, no patient had significant forward protrusion of the posterior corneal surface a mean of 14 months after LASIK. The posterior cornea in post-LASIK myopic eyes was very stable. Contrary to results in previous studies, progressive changes to the posterior corneal surface did not routinely occur after LASIK performed within established parameters.

Thin Head and Single Use Microkeratomes Reduce Epithelial Defects During LASIK

PURPOSE

To evaluate the effect of microkeratome design and head dimension (flap thickness) on the rate of epithelial defects.

METHODS

A retrospective review of 4000 LASIK procedures performed between May 2000 and December 2003 was conducted. Intraoperative epithelial defects were identified in 326 cases. The microkeratome design (reusable vs disposable) and head dimensions (100, 130, and 150 micron) were recorded along with age, sex, central ultrasonic pachymetry, keratometry, preoperative refraction (sphere, cylinder, and axis), and Schirmer testing. The chi-square and Student t test were used in data analysis.

RESULTS

A total of 326 (8.2%) procedures had an associated epithelial defect. With the reusable microkeratome, heads that produced thinner flaps were associated with a lower incidence of epithelial defects (P<.05 for all three groups, 100, 130 and 150 micron head). When compared to a reusable head of the same dimension and to the entire population of reusable heads, the disposable 130 head exhibited a significantly lower rate of epithelial defects (P<.0001).

CONCLUSIONS

The results of this study support that both microkeratome design and head dimension (and resulting corneal flap thickness) play a role in the formation of epithelial defects. These are surgeon selectable factors, unrelated to technique or patient risk factors, which can be used to reduce the rate of epithelial defects and associated complications.