Age a factor in keratoconus complications

Fort Lauderdale, FL-Younger age appears to be associated with the development of corneal scarring, corneal steepening, and the need for penetrating keratoplasty in patients with keratoconus, according to a study conducted by Karla Zadnik, OD, PhD.

"Contrary to what we might think of with a chronic disease, those patients whose disease is diagnosed when they are young tend to have worse keratoconus. We would expect their disease to progress more quickly, and their time frame to needing a penetrating keratoplasty would be shorter," said Dr. Zadnik, Glenn A. Fry Professor in Optometry and Physiological Optics at The Ohio State University College of Optometry, Columbus, OH. She spoke during the Association for Research in Vision and Ophthalmology annual meeting in Fort Lauderdale, FL.

She and colleagues examined evidence from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study to determine if age at study entry was correlated with worse disease, faster disease progression, and/or a shorter time to penetrating keratoplasty. Previous retrospective studies showed conflicting results, with one finding no association between young age and disease severity and another finding a positive association.

Outcomes evaluated included incident corneal scarring, penetrating keratoplasty, change in visual acuity, and change in corneal curvature (first definite apical clearance lens, or FDACL).

For purposes of this study, entry criteria included having an irregular cornea in at least one eye plus a slit lamp sign characteristic of keratoconus such as Vogt's striae, Fleischer's ring, or corneal scarring in at least one eye. Patients with one corneal transplant were eligible, but not those who had undergone bilateral transplants.

Incident scarring was evaluated on the basis of having at least one eye at baseline that had not undergone penetrating keratoplasty or that had undergone at least two annual exams before keratoplasty was performed. Patients with corneal scarring at baseline were excluded from analysis for this outcome; by those criteria, 882 patients were available. For analysis of corneal curvature, 1,020 patients were included, and 1,065 were evaluated for visual acuity.

The average age of patients at baseline was 39 years; approximately 65% of the 1,209 patients enrolled were between 30 and 49 years old, about 20% were under 30 years old, and about 15% were 50 years or older.

The results showed that a younger age at baseline was associated with a higher incidence of corneal scarring. "Among patients less than 25 years old, one-third had corneal scars, and among patients older than 25 years, only 18% of them developed a corneal scar over the 8 years of the study," Dr. Zadnik said. "That resulted in an odds ratio of almost 3 times associated with being less than 25 years or 25 years or older in a multivariate model, even when controlling for corneal staining, FDACL, rigid contact lenses, and low-contrast entrance acuity."

PK incidence

Examining the incidence of penetrating keratoplasty, investigators saw an approximate 39% increased risk for each decade of younger age. The 8-year incidence of penetrating keratoplasty was 15% among patients 40 years old or younger compared with 8% among patients 40 years old or older.

"You may interpret that as once your patients have gotten to a certain age, the likelihood of them subsequently needing a corneal transplant decreases. Older age is protective, and a younger age is a risk factor," Dr. Zadnik said.

Results of the analysis for corneal curvature or FDACL showed 35% of patients 35 years old or younger have had a bad outcome (an increase in curvature of at least 3 D over the study period), compared with 18% of older patients. There was about a 2.5 times higher risk of increased corneal curvature associated with younger age.

However, in a surprising finding, there were no significant associations with younger age for any of the visual acuity measures used in the analysis, Dr. Zadnik said.