Effects of central corneal thickness on measurement of intra-ocular pressure in keratoconus and post-keratoplasty

Ophthalmic Physiol Opt. 1999 May;19(3):236-41. doi: 10.1046/j.1475-1313.1999.00420.x.

Abstract

Purpose: To measure and compare central corneal thickness (CT) and intraocular pressure (IOP) in keratoconus and post-keratoplasty subjects and examine the CT-IOP relationship.

Methods: 22 keratoconus (category I: six female sixteen male, average age 27.0 range 12-47) and 19 post-keratoplasty (category II: ten female nine male average age 34.6 range 16-54) patients without other anterior segment conditions were recruited. Only one, non-contact lens wearing, eye of the patient was included for analysis. Cornea was anaesthetised with non-preserved 0.4% Benoxinate Hydrochloride. Using a randomised approach, CT was measured using a standard ultrasonic pachymeter. IOP was then measured using a standard Goldmann tonometer. At all times the tonometrist remained unaware of the corneal thickness values.

Results: The mean (+/- s.d.) values for CT and IOP respectively in the two categories were: (I), 445 (45) mu and 9.8 (2.3) mmHg, (II), 564(44) microns and 15.8 (3.9) mmHg. Differences between I and II for both CT and IOP were significant (t-test, p = 0.01). Within each category, a significant correlation between CT and IOP was not found. Pooling all pairs of data (n = 41) a significant relationship between CT and IOP was detected (r = 0.635, p = 0.0001).

Conclusion: The results confirm the hypothesis that an eye with a thicker cornea tends to present with a higher measured IOP. In the management of keratoconus and other corneal surgical procedures, changes in CT will contribute to any apparent changes in measured IOP.

MeSH terms

  • Adolescent
  • Adult
  • Child
  • Cornea / diagnostic imaging
  • Cornea / pathology*
  • Corneal Transplantation*
  • Female
  • Humans
  • Intraocular Pressure*
  • Keratoconus / pathology*
  • Keratoconus / physiopathology
  • Male
  • Middle Aged
  • Postoperative Period
  • Tonometry, Ocular
  • Ultrasonography