Intraocular Pressure Measurements Using Dynamic Contour Tonometer After Photorefractive Keratectomy

Hyun Joon Choi; Sun Woong Kim; Tae Im Kim; Eung Kweon Kim

doi:10.3341/jkos.2008.49.4.577

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Choi, Kim, Kim, and Kim: Intraocular Pressure Measurements Using Dynamic Contour Tonometer After Photorefractive Keratectomy

Original Article

J Korean Ophthalmol Soc 2008;49(4):577-582.

Published online: 7 September 2008

DOI: https://doi.org/10.3341/jkos.2008.49.4.577

Intraocular Pressure Measurements Using Dynamic Contour Tonometer After Photorefractive Keratectomy

Hyun Joon Choi, M.D.¹, Sun Woong Kim, M.D.², Tae Im Kim, M.D.², Eung Kweon Kim, M.D.²

¹National Health Insurance Corporation Ilsan Hospital, Gyeonggi, Korea

²The Institute of Vision Research, Department of Ophthalmology, College of Medicine, Yonsei University, Seoul, Korea

Address reprint requests to Eung Kweon Kim, M.D. Department of Ophthalmology, Severance Hospital, College of Medicine, Yonsei University #134 Shinchon-dong, Seodaemun-gu, Seoul 120-752, Korea Tel: 82-2-2228-3577, Fax: 82-2-312-0541, E-mail: eungkkim@yumc.yonsei.ac.kr

Received 31 May 2007 Accepted 16 October 2007

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To assess the performance of the dynamic contour tonometer (DCT) in eyes undergoing excimer laser photorefractive keratectomy (PRK).

Methods

Intraocular pressure (IOP) was measured in 30 eyes after first‐ time excimer laser PRK pre‐ and three months post‐ operatively using Goldmann applanation tonometer (GAT), noncontact air tonometer (NCT), and the DCT.

Results

There was significant correlation between central corneal thickness (CCT) and IOP measurements by GAT and NCT (CCT vs GAT: r²=0.31, p<0.01, CCT vs NCT: r²=0.39, p<0.01). However, the correlation between CCT and IOP measurements by DCT was not significant (CCT vs DCT: r²=0.14, p=0.32). After PRK, the mean change in CCT and IOP measurements using GAT, NCT, DCT were 73.70±26.92 µm (mean±SD), 2.43±2.86 mmHg (p<0.01), 3.83±2.34 mmHg (p<0.01) and 0.44±1.51 mmHg (p=0.125), respectively. The preoperative and postoperative DCT measurements did not differ significantly.

Conclusions

The reduction in CCT induced by PRK doesn't appear to influence DCT measurements; therefore, DCT may be better suited over GAT or NCT for monitoring IOP in eyes that underwent refractive surgery.

Keywords: Central corneal thickness, Pascal dynamic contour tonometer, Photorefractive keratectomy

References

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Figure 1.

Pre- and post-PRK IOP measurements by GAT, NCT, and DCT (mean±SD). The decrease in GAT and NCT measurements after PRK was statistically significant (* ^† p<0.01). The DCT measurements preoperatively p<0.01, and postoperatively did not differ significantly (^‡ p=0.125). Box plots of median (center line), 25th and 75th percentile values (bottom and top lines) and range of values (brackets); PRK=photorefractive keratectomy; IOP=intraocular pressure; CCT=central corneal thickness; GAT=Goldmann applanation tonometric intraocular pressure; NCT=non-contact tonometric intraocular pressure; DCT=dynamic contour tonometric intraocular pressure.

Figure 2.

Correlation between changes in IOP readings and reduction of CCT after PRK as measured by GAT, NCT and DCT. Most of the DCT values lay within ±2 mm Hg from the preoperative baseline values, whereas most change of GAT and NCT lay below this boundary, indicating an underestimation of IOP in the treated eye; PRK= photorefractive keratectomy; IOP=intraocular pressure; CCT= central corneal thickness; GAT=Goldmann applanation tonometric intraocular pressure; NCT=non‐ contact tonometric intraocular pressure; DCT=dynamic contour tonometric intraocular pressure.

Figure 3.

Correlation of tonometer readings with CCT. The IOP measurements by GAT and NCT were significantly affected by CCT (GAT vs CCT; r²=0.31, p<0.01, y=0.027×-1.662, NCT vs CCT; r²=0.39, p<0.01, y=0.044× −10.32). The IOP measurements by DCT were not statistically affected by CCT (r²=0.029, p=0.195, y=-0.008x+20.79); IOP= intraocular pressure; CCT=central corneal thickness; GAT= Goldmann applanation tonometric intraocular pressure; NCT= non-contact tonometric intraocular pressure; DCT=dynamic contour tonometric intraocular pressure.

Table 1.

Preoperative demographic and clinical data of subjects

Number	24 patients (30 eyes)
Sex (M:F)	8:16
Age (years)	27.8±7.4 (23∼33)
Ref (D)	‐5.99±1.66 (−2.13 to −8.63)
Ablation depth (μ m)	66.27±18.36 (21∼98)

Data are expressed as the mean±SD, with the range in parentheses; Ref=refractive error; D=diopter spherical equivalent.

Table 2.

Difference between pre- and post-PRK clinical data of subjects

	Pre-PRK	Post-PRK	Δ	p^*
GAT (mmHg)	13.70±2.77 (10∼17)	11.30±2.11 (8∼15)	‐2.43±2.86	<0.01
NCT (mmHg)	14.40±2.22 (10∼19)	10.57±1.92 (7∼14)	‐3.83±2.34	<0.01
DCT (mmHg)	16.26±2.22 (13.0∼20.5)	16.69±2.37 (12.2∼21.8)	0.44±1.51	0.125
CCT (μ m)	552.37±20.40 (521∼601)	478.67±34.01 (411∼547)	‐73.70±26.92	<0.01

Data are expressed as the mean±SD, with the range in parentheses; PRK=photorefractive keratectomy; Δ=Difference between pre- and post-PRK data; CCT=central corneal thickness; GAT=Goldmann applanation tonometric intraocular pressure; NCT= non-contact tonometric intraocular pressure; DCT=dynamic contour tonometric intraocular pressure

^* t-test.

Table 3.

Measured and corrected GAT

	Pre-PRK	Post-PRK	Δ
GAT, measured (mmHg)	13.70±2.77	11.30±2.11	−2.43±2.86
GAT, corrected (mmHg)^*	13.37±1.79	14.62±2.69	1.25±3.34

Data are expressed as the mean±SD, with the range in parentheses; PRK=photorefractive keratectomy; Δ=difference between pre- and post-PRK data; GAT=Goldmann applanation tonometric intraocular pressure

^* calculated by following correction formula: corrected IOP=measured IOP–(CCT–545) /50×2.5 mmHg.²³; IOP=intraocular pressure.

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