Comparison of Three Tonometers in Measuring Intraocular Pressure in Eyes That Underwent Myopic Laser in situ Keratomileusis and Photorefractive Keratectomy

Figures & data

Table 1 Baseline Characteristics of Eyes That Had LASIK and PRK

Parameters	LASIK (n=60)	PRK (n=60)	p
Age, years	29.7±7.6 (18 to 50)	29.2±8.1 (19 to 52)	0.727
Gender, male: female	20M:40F	19M:41F	0.845
MRSE, diopter	−3.9±1.4 (−1 to −7.6)	−5.2±1.7 (−1.4 to −8.3)	*0.000
CCT, um	563.8±22.1 (523 to 606)	540.7±32.6 (488 to 616)	*0.000
Km, diopter	43.4±1.1 (41.2 to 45.6)	43.4±1.2 (41 to 47.1)	0.883
Maximum Ablation depth, um	79.6±21.7 (36 to 129)	90.7±26.7 (38 to 148)	*0.013

Note: *Statistically significant.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; M, male; F, female; MRSE, manifest refraction spherical equivalent; CCT, central corneal thickness; um, micrometer; Km, mean corneal curvature.

Table 2 Baseline IOP of Eyes That Had LASIK and PRK

Parameters	LASIK (n=60)	PRK (n=60)	p (inter)
IOP, mm Hg
GAT	15.1±3 (8 to 20)	14.4±2.6 (8 to 20)	0.155
CATS	16.4±2.8 (10 to 22)	15.9±2.6 (10 to 21)	0.309
CVS-bIOP	14.8±2.4 (9 to 21.5)	14.2±2.4 (9.4 to 19.9)	0.200
p value (intra)	*0.003	*0.000

Note: *Statistically significant.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; IOP, intraocular pressure; GAT, Goldmann applanation tonometer; CATS, correcting applanation tonometer surface; CVS-bIOP, Corvis ST biomechanically corrected IOP.

Table 3 Pearson Correlation Analysis of Preoperative Mean IOP Measurements Between 2 Tonometers (Tonometer Pairs)

Parameter	LASIK (n=60)		PRK (n=60)
	r Value	p value	r Value	p value
Pre-operative
GAT vs CATS	0.865	*0.000	0.939	*0.000
GAT vs CVS-bIOP	0.589	*0.000	0.370	*0.004
CATS vs CVS-bIOP	0.571	*0.000	0.286	*0.027

Note: *Statistically significant.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; IOP, intraocular pressure; GAT, Goldmann applanation tonometer; CATS, correcting applanation tonometer surface; CVS-bIOP, Corvis ST biomechanically corrected IOP.

Figure 1 Bland Altman analysis of the difference in preoperative IOP measurements of tonometer pairs (A and B) GAT-CATS, (C and D) GAT-CVS-bIOP and (E and F) CATS-CVS-bIOP in LASIK and PRK.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; IOP, intraocular pressure; GAT, Goldmann applanation tonometer; CATS, correcting applanation tonometer surface; CVS-bIOP, Corvis ST biomechanically corrected IOP.

Table 4 Changes in IOP Before and After LASIK or PRK

Parameter	LASIK (n=60)		PRK (n=60)
	Mean ±SD (Range)	p	Mean ±SD (Range)	p
GAT, mm Hg
Preop	15.1±3 (8 to 20)	*0.000	14.4±2.6 (8 to 20)	*0.000
Postop	11.3±2.1 (8 to 18)		12.1±3 (6 to 19)
CATS, mm Hg
Preop	16.4±2.8 (10 to 22)	*0.000	15.9±2.6 (10 to 21)	*0.000
Postop	13.1±2.3 (10 to 19)		13.7±3 (6 to 19)
CVS-bIOP, mm Hg
Preop	14.8±2.4 (9 to 21.5)	*0.000	14.2±2.4 (9.4 to 19.9)	*0.000
Postop	12.9±1.5 (9.7 to 16.4)		12.6±1.9 (8.5 to 16.7)

Note: *Statistically significant.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; IOP, intraocular pressure; GAT, Goldmann applanation tonometer; CATS, correcting applanation tonometer surface; CVS-bIOP, Corvis ST biomechanically corrected IOP.

Table 5 Pearson Correlation Analysis of Preoperative and Postoperative Measurements of Each Tonometer

Parameter	FS-LASIK (n=60)		PRK (n=60)
	r Value	p value	r Value	p value
Preop GAT vs Postop GAT	0.356	*0.005	0.286	*0.027
Preop CATS vs Postop CATS	0.435	*0.001	0.407	*0.000
Preop CVS-bIOP vs Postop CVS-bIOP	0.562	*0.000	0.610	*0.000

Note: *Statistically significant.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; IOP, intraocular pressure; GAT, Goldmann applanation tonometer; CATS, correcting applanation tonometer surface; CVS-bIOP, Corvis ST biomechanically corrected IOP.

Figure 2 Bland Altman analysis of the difference in preoperative and postoperative IOP measurements per tonometer (A and B) GAT, (C and D) CATS and (E and F) CVS-bIOP in LASIK and PRK.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; IOP, intraocular pressure; GAT, Goldmann applanation tonometer; CATS, correcting applanation tonometer surface; CVS-bIOP, Corvis ST biomechanically corrected IOP.

Table 6 Pearson Correlation Analysis of Postoperative Mean IOP Measurements Between 2 Tonometers (Tonometer Pairs)

Parameter	LASIK (n=60)		PRK (n=60)
	r Value	p value	r Value	p value
Post-Operative
GAT vs CATS	0.852	*0.000	0.921	*0.000
GAT vs CVS-bIOP	0.233	0.073	0.450	*0.000
CATS vs CVS-bIOP	0.176	0.179	0.487	*0.000

Note: *Statistically significant.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; IOP, intraocular pressure; GAT, Goldmann applanation tonometer; CATS, correcting applanation tonometer surface; CVS-bIOP, Corvis ST biomechanically corrected IOP.

Table 7 Pearson Correlation Analysis of Percentage Change (%Δ) Before and After LASIK and PRK  Between 2 Tonometers (Tonometer Pairs)

Parameter	LASIK (n=60)		PRK (n=60)
	r Value	p value	r Value	p value
%Δ
GAT vs CATS	0.818	*0.000	0.907	*0.000
GAT vs CVS-bIOP	0.346	*0.000	0.126	0.338
CATS vs CVS-bIOP	0.335	*0.009	0.003	0.800

Note: *Statistically significant.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; IOP, intraocular pressure; GAT, Goldmann applanation tonometer; CATS, correcting applanation tonometer surface; CVS-bIOP, Corvis ST biomechanically corrected IOP.

Table 8 Changes in MRSE, CCT and Km Before and After LASIK and PRK

Parameter	LASIK (n=60)		PRK (n=60)
	Mean ±SD (Range)	^p	Mean ±SD (Range)	^p
MRSE, diopter
Preop	−3.9±1.4 (−1 to −7.6)	*0.000	−5.2±1.7 (−1.4 to −8.3)	*0.000
Postop	−0.3±0.2 (0 to −0.8)		−0.1±0.3 (0.9 to −0.9)
Change (Δ1)	−3.7±1.4 (−0.9 to −7)		−5.1±1.7 (−1.6 to −8.1)
CCT, um
Preop	563.8±22.1 (523 to 606)	*0.000	540.7±32.6 (488 to 616)	*0.000
Postop	496.1±28.5 (447 to 559)		446.3±36.2 (361 to 533)
Change (Δ2)	−67.7±20.5 (−111 to −31)		−94.4±25.9 (−142 to −34)
Km, diopter
Preop	43.4±1.1 (41.2 to 45.6)	*0.000	43.4±1.2 (41 to 47.1)	*0.000
Postop	40.5±1.4 (36.7 to 43.5)		38.9±1.9 (35.4 to 42.5)
Change (Δ2)	−2.9±0.9 (−4.8 to −1.3)		−4.5±1.2 (−6.7 to −2)

Notes: ^p value comparing preop and post parameters only. Δ1 Difference of Preop and postop. Δ2 Difference of Postop and preop. *Statistically significant.

Abbreviations: MRSE, manifest refraction spherical equivalent; CCT, central corneal thickness; um, micrometer; Km, mean corneal curvature.

Table 9 Percentage Change (%Δ) in MRSE, CCT and Km Before and After LASIK or PRK (Inter)

Parameter	LASIK (n=60)	PRK (n=60)
	Mean ±SD (Range)	Mean ±SD (Range)	p (inter)
Percentage change (%Δ)
MRSE, diopter (%Δ1)	−92.6±6.2 (−73.9 to −100)	−97.8±8.4 (−68.2 to −127.3)	*0.000
CCT, um (%Δ2)	−12±3.6 (−5.5 to −19.1)	−17.4±4.7 (−6.3 to −26.3)	*0.000
Km, diopter (%Δ2)	−6.6±2.1 (−3.1 to −10.9)	−10.5±2.8 (−4.5 to −15.7)	*0.000

Notes: Δ1 Difference of Preop and postop. Δ2 Difference of Postop and preop. *Statistically significant.

Abbreviations: LASIK, laser assisted in situ keratomileusis; PRK, photorefractive keratectomy; MRSE, manifest refraction spherical equivalent; CCT, central corneal.

Table 10 Pearson Correlation Analysis Between Percentage Change (%Δ) in IOP Measurements versus Percentage Change (%Δ) in MRSE, CCT and Km in LASIK and PRK

Percentage Change (%Δ)	LASIK						PRK
	%Δ1 MRSE		%Δ2 CCT		%Δ2 Km		%Δ1 MRSE		%Δ2 CCT		%Δ2 Km
	r Value	p value	r Value	p value	r Value	p value	r Value	p value	r Value	p value	r Value	p value
GAT (%Δ1)	−0.211	0.106	0.135	0.304	0.131	0.318	−0.104	0.428	−0.068	0.603	−0.206	0.114
CATS (%Δ1)	−0.186	0.156	0.007	0.958	−0.065	0.624	0.005	0.967	−0.03	0.82	0.155	0.238
CVS-bIOP (%Δ1)	−0.347	*0.007	0.069	0.598	0.061	0.646	0.131	0.317	0.079	0.551	0.033	0.803

Notes: *Statistically significant. Δ1 Difference of Preop and postop.

Abbreviations: LASIK, laser in situ keratomileusis; PRK, photorefractive keratectomy; IOP, intraocular pressure; GAT, Goldmann applanation tonometer; CATS, correcting applanation tonometer surface; CVS-bIOP, Corvis ST biomechanically corrected IOP.