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


CONCLUSIONS
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.
Patel
S
S
Academic Unit of Ophthalmology, Birmingham and Midland Eye Centre, City Hospital NHS Trust, UK. Dr_SPatel@compuserve.com
McLaughlin
J M
JM
D000293:Adolescent; D000328:Adult; D002648:Child; D003315:Cornea / Q000000981:diagnostic imaging / Q000473:pathology*; D016039:Corneal Transplantation; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D007640:Keratoconus / Q000473:pathology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D014065:Tonometry, Ocular; D014463:Ultrasonography