Comparison of IOP after PRK with four different tonometers Wilford Hall Medical Center, San Antonio, TX 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.
Introduction Background • 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. Tono-Pen Pneumatonometer DCT Perkins
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
Method IOP measured by each device at 10, 20, 30, and 40 mmHg. DCT Pneumatonometer Tono-Pen Perkins
Results P< .05 (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.
Results Tono-Pen Pascal (Sdve 7.3) (Sdve 5.3) (Sdve 7.4) (Sdve 2.5)
Results Tono-Pen Pascal (Sdve 10.2) (Sdve 5.9) (Sdve 5.8) (Sdve 4.1)
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
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. Conclusion
References • Abbasoglu OE et al.Ophthalmology. 1998 Dec;105(12):2193-6 • Garzozi HJ et al. Cornea. 2001 Jan;20(1):33-6. • Kao SF et al. Ophthalmology 1987;94:1541-1544 • Kaufmann C et al. Invest Ophthalmol Vis Sci. 2003 Sep;44(9):3790-4. • Kaufmann C et al. Invest Ophthalmol Vis Sci. 2004 Sep;45(9):3118 • Levy Y et al. J Cataract Refract Surg. 1999 Apr;25(4):486-91. • Mardelli PG et al. Ophthalmology. 1997 Jun;104(6):945-8. • Schipper I et al. J Refract Surg 1995; 11:366-70 • Stahl J et al. J Cataract Refract Surg 2000; 26:736-743 • Schipper I, et al. J Cataract Refract Surg. 2000 Jun;26(6):929-33. • Siganos DS et al. J Cataract Refract Surg. 2004 Apr;30(4):746-51 • www.haag-streit-usa.com accessed March 4, 2008. • www.reichert.com accessed March 4, 2008. • www.ziemergroup.ch accessed March 4, 2008.