Underestimation of intraocular pressure after photorefractive keratectomy: a biomechanical analysis.
Excimer laser surgery, to correct corneal refraction, induces changes in corneal thickness and curvature. Both factors can cause measurement errors when determining intraocular pressure (IOP). This study evaluates effects of photorefractive keratectomy (PRK) on IOP measurements, using Goldmann applanation tonometry (GAT) and Applanation resonance tonometry (ART), in an in vitro model. Six porcine eyes was enucleated and pressurised to a constant IOP=30 mmHg. After removal of the epithelium, the eyes were PRK-treated for a total of 25 dioptres. The measured IOP decreased 13.2 mmHg for GAT and 9.0 mmHg for ART. The total underestimation by GAT was larger than for ART, and a part of the ART underestimation (3.5 mmHg) was assigned to sensitivity to the change in corneal surface structure resulting from the removal of epithelium. The flat contact probe of GAT, as compared with the convex tip of ART, provided explanation for the difference in IOP measurement error after PRK.
Hallberg
Per
P
Department of Biomedical Engineering and Informatics, University Hospital, Umeå, 901 85, Sweden. per.hallberg@vll.se
Eklund
Anders
A
Santala
Kenneth
K
Koskela
Timo
T
Lindahl
Olof
O
Lindén
Christina
C
D000818:Animals; D001696:Biomechanical Phenomena; D002102:Cadaver; D007429:Intraocular Pressure / Q000502:physiology*; D054018:Lasers, Excimer; D008433:Mathematics; D023421:Models, Animal; D018903:Photorefractive Keratectomy; D012029:Refraction, Ocular / Q000502:physiology; D014065:Tonometry, Ocular / Q000379:methods