To assess corneal viscous damping and corneal rigidity following SubBowmans Keratomileusis SBK and P

1
Corneal Biomechanical Properties and Intraocular
Pressure following SBK and PRK Allen J.
Boghossian D.O., Daniel S. Durrie, M.D.
Purpose
Results
Intraocular Pressure - SBK
Corneal Hysteresis (CH)
To assess corneal viscous damping and corneal
rigidity following Sub-Bowmans Keratomileusis
(SBK) and PRK measured with the Ocular Response
Analyzer and comparison of intraocular pressure
(IOP) measurement by Goldman Applanation
Tonometer (GAT), Ocular Response Analyzer (ORA)
and Pascal Dynamic Tonometer (PDT).
The mean MRSE before surgery was -4.18 1.03 D
for SBK eyes and -4.30 1.04 D for PRK eyes. At
preoperative examination, the average CH was 10.4
3.1 for SBK eyes and 10.5 2.6 for PRK eyes.
At 1 month, the average CH was 7.8 2.1 for SBK
eyes and 7.5 3.2 for PRK eyes. At
preoperative examination, the average CFR was
11.1 2.5 for SBK eyes and 11.0 2.3 for PRK
eyes. At 1 month, the average CFR was 7.0 2.0
for SBK eyes and 6.8 2.4 for PRK eyes. The
average IOP measured by GAT decreased by 10 in
SBK eyes and 8 in PRK eyes. The average IOP
measured by ORA decreased by 36 in SBK eyes and
27 in PRK eyes. The average IOP measured by PDT
decreased by 5 in SBK eyes and increased by 3
in PRK eyes.
Corneal Resistance Factor (CFR)
Intraocular Pressure - PRK
Methods
Twenty five patients in a prospective,
randomized, clinical study underwent refractive
surgery with Intralase assisted SBK with a 110
micron flap thickness in one eye and PRK in the
fellow eye. All patients were measured for
Corneal Hysteresis (CH), which is a measure of
viscous damping in the cornea, and for Corneal
Resistance Factor (CFR) which is a measure of
overall corneal rigidity, at pre-op and 1 month
post-op using the ORA. Intraocular pressure
measurements were compared using GAT, PDT and ORA
at pre-op and 1 month post-op. The ORA utilizes a
rapid air impulse, and an electro-optical system
to record applanation pressure. The PDT uses a
solid-state pressure sensor, built into the
center of a contoured, concave tip surface, to
directly measure IOP.
Change in Intraocular Pressure
Change in Corneal Biomechanics
Conclusion
There is a decrease in viscous damping and cornea
rigidity measured by the ORA after SBK and PRK.
However, the difference between the eyes was not
statistically significant. Both GAT and ORA
underestimated IOP after SBK and PRK.
Intraocular pressure measured by PDT was most
consistent from pre-op to post-op.
Goldman Applanation Tonometer (GAT)
Ocular Response Analyzer (ORA)
Pascal Dynamic Tonometer (PDT)