Comparison of IOP after PRK with four different tonometers

Marcus C. Neuffer, M.D., Paul Drayna M.D.,

Vasudha Panday M.D., Charles Reilly, M.D

All authored materials constitute the personal statements of the author and are not intended to constitute an endorsement by the 59th Medical Wing, the U.S. Air Force, or any other Federal Government entity.

The authors have no financial interests or relationships to disclose.

Wilford Hall Medical Center, San Antonio, TX

IntroductionBackground

– Studies have questioned the accuracy of tonometers, such as Goldmann applanation, in measuring intraocular pressure (IOP) in post-excimer laser treated eyes.

– The dynamic contour tonometer (DCT) is an electronic pressure sensor that measures IOP independent of corneal thickness.

Purpose – Compare the accuracy of the DCT with three other tonometers in

measuring IOP in post photorefractive keratectomy (PRK) rabbit eyes.

PerkinsTono-Pen PneumatonometerDCT

Method

• 16 rabbits received a standard 6.0mm 100μm depth PRK ablation OD– The left eye was the

control

• Four weeks later – Ablation confirmed by

pachymetery – IOPs measured in both

treated and control eyes

Method– Eyes cannulated with pressure transducer and a syringe

containing balanced salt solution (BSS)– IOPs of 10, 20, 30 and 40 mmHg created with BSS infusion

Pressure Transducer BSS infusion

MethodIOP measured by each device at 10, 20, 30, and 40 mmHg.

DCT Pneumatonometer

Tono-Pen Perkins

Results

(Sdve 2.5) (Sdve 2.7) (Sdve 1.9) (Sdve 2.5)

Data analyzed using a repeated measures analysis of variance (RM ANOVA) of the mean absolute difference between the tonometers and corresponding pressure transducer measurement.

P< .05

Results

0.00

5.00

10.00

15.00

20.00

25.00

30.00

Pneumatonometer Perkins

mea

n a

bs

diff

eren

ce (

mm

HG

)

PressureTransducer 20 mmHg OD

(Sdve 7.3) (Sdve 5.3) (Sdve 7.4) (Sdve 2.5)

PascalTono-Pen

Results

(Sdve 10.2) (Sdve 5.9) (Sdve 5.8) (Sdve 4.1)

Tono-Pen

Pascal

Results

(Sdve 7.4) (Sdve 8.8) (Sdve 10.0) (Sdve 5.6)

Results

All four tonometers demonstrated a statistically significant increase in mean absolute difference with higher IOP

Conclusion

• There was no statistically significant difference between the DCT, Tono-Pen, and Pneumatonometer at any of the IOP levels in the treated eyes.

• There was a statistically significant difference (p<.05) between the Perkins tonometer and the other three tonometers at 10 mmHg in the treated eyes.– The Perkins tonometer tended to underestimate IOP.

• All of the tonometers showed a significant (P<.05) increase in the mean absolute deviation from the pressure transducer at higher IOP levels (30 - 40 mmHg) in both the treated and control eyes.

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