Tonometry: an overview

Singh, Parul

doi:10.9790/0853-13116770

Cited by 4 publications

(3 citation statements)

References 18 publications

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“…However, none of these features holds true with the cornea. 3 , 4 , 7 Several studies have shown that GAT is affected by corneal properties like central corneal thickness (CCT), 8 , 9 where IOP readings tend to overestimated or underestimated in thick and thin corneas. Along with CCT, other parameters that may influence IOP readings were corneal curvature, tear film and biomechanical properties of the cornea.…”

Section: Introductionmentioning

confidence: 99%

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

Ang¹,

Bargas²,

Martinez³

et al. 2022

OPTH

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Objective To compare the intraocular pressure (IOP) obtained by Goldmann applanation tonometer (GAT), correcting applanation tonometer surface (CATS) and biomechanically corrected IOP (bIOP) of Corvis ST tonometer (CVS); and to determine the effects of manifest refraction spherical equivalent (MRSE), central corneal thickness (CCT) and mean corneal curvature (Km) on the IOP measurements of corneal refractive patients. Methods This was a single-center, retrospective, cross-sectional study of 120 eyes of 64 patients from May 1, 2020 to June 1, 2021 who underwent laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). The level of agreement between the three tonometers was evaluated, and correlation between parameters was calculated using Pearson correlation. Results Mean preoperative to postoperative IOP in LASIK and PRK was 15.1 ± 3 to 11.3 ± 2.1 and 14.4 ± 2.6 to 12.1 ± 3 using GAT, 16.4 ± 2.8 to 13.1 ± 2.3 and 15.9 ± 2.6 to 13.7 ± 3 using CATS and 14.8 ± 2.4 to 12.9 ± 1.5 and 14.2 ± 2.4 to 12.6 ± 1.9 using CVS-bIOP. Preoperative IOP correlation between each tonometer pair showed that the lowest mean difference was between GAT and CVS-bIOP (0.32 in LASIK, 0.15 in PRK). Preoperative to postoperative IOP correlation of each tonometer resulted in a difference of 3.77, 2.30 in GAT; 3.32, 2.28 in CATS and 1.88, 1.62 in CVS-bIOP in the LASIK and PRK groups, respectively. Percentage change in CCT and Km was not correlated while change in MRSE had a weak relationship with percentage change in CVS-bIOP. Conclusion Preoperatively, GAT and CVS-bIOP had the best agreement in IOP measurements. CATS recorded the highest IOP preoperatively and postoperatively. IOP decreased in the three tonometers after LASIK and PRK with GAT having the largest decrease. CVS-bIOP had the lowest change between preoperative and postoperative IOP measurements. Only percentage change in MRSE was correlated with percentage change in CVS-bIOP in the LASIK group.

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Section: Introductionmentioning

confidence: 99%

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

Ang¹,

Bargas²,

Martinez³

et al. 2022

OPTH

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show abstract

“…The applanation type IOP measurement method shown in Fig 1B was developed by Goldman, a Swiss ophthalmologist in 1955 to compensate for the disadvantages of an indentation type system [ 13 ]. This method in which a pressure body is brought into direct contact with an eyeball determines the IOP as the force F 1 required to flatten a constant area (3.06 mm 2 ) of the cornea divided by the flattened area [ 14 ]. It is now known to be the most accurate and precise method and is being used as the gold standard for IOP measurement [ 15 ].…”

Section: Introductionmentioning

confidence: 99%

New intraocular pressure measurement method using reflected pneumatic pressure from cornea deformed by air puff of ring-type nozzle

2017

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In this study, a non-contact type intraocular pressure (IOP) measuring system using reflected pneumatic pressure is proposed to overcome the disadvantages of existing measurement systems. A ring-type nozzle, a key component in the proposed system, is designed via computational fluid analysis. It predicts the reflected pneumatic pressure based on the nozzle exit angle and inner and outer diameters of the nozzle, which are 30°, 7 mm, and 9 mm, respectively. Performance evaluation is conducted using artificial eyes fabricated using polydimethylsiloxane with the specifications of human eyes. The IOP of the fabricated artificial eyes is adjusted to 10, 30, and 50 mm Hg, and the reflected pneumatic pressure is measured as a function of the distance between the ring-type nozzle and artificial eye. The measured reflected pneumatic pressure is high when the measurement distance is short and eye pressure is low. The cornea of an artificial eye is significantly deformed at a low IOP, and the applied pneumatic pressure is more concentrated in front of the ring-type nozzle because of the deformed cornea. Thus, the reflected pneumatic pressure at a low IOP has more inflows into the pressure sensor inserted inside the nozzle. The sensitivity of the output based on the IOP at measurement distances between 3–5 mm is -0.0027, -0.0022, -0.0018, -0.0015, and -0.0012. Sensitivity decreases as the measurement distance increases. In addition, the reflected pneumatic pressure owing to the misalignment at the measurement distances of 3–5 mm is not affected within a range of 0.5 mm. Therefore, the measurement range is acceptable up to a 1 mm diameter from the center of an artificial eye. However, the accuracy gradually decreases as the reflected pneumatic pressure from a misalignment of 1 mm or more decreases by 26% or more.

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“…It is due to this unawareness that Glaucoma is so prevalent. Existing diagnosis methods like Tonometry [3], Ophthalmoscopy [4] and Perimetry [5] are cumbersome and time-consuming for the patient and has significant error rates. So, a technique is needed to detect Glaucoma automatically by analyzing the digital fundus retinal image of a human eye.…”

Section: Introductionmentioning

confidence: 99%

A Threshold based Algorithm to Detect Peripapillary Atrophy for Glaucoma Diagnosis

Majumdar¹

2015

IJCA

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The presence of a Peripapillary Atrophy (PPA) is one of the conditions for Glaucoma to develop. This paper is divided into three parts. The first part of this paper describes the terminology related to the diagnosis of glaucoma. The second part of this paper describes various existing algorithms to detect and segment human PPA from a digital fundus retinal image. The paper compares the performances and contrasts the various shortcomings of these described algorithms. The third part of this paper proposes a threshold-based algorithm to detect the PPA of a human eye to aid the diagnosis of Glaucoma. The proposed algorithm calculates the Red by Green ratio for each pixel in the Region of Interest (ROI) and segments the Optic Disc (OD) from the PPA, having different pixel ratios. The algorithm can be further improved by applying sub-algorithms of false region elimination. The proposed algorithm should, theoretically, overcome most of the problems faced by the described algorithms.

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Tonometry: an overview

Cited by 4 publications

References 18 publications

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

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

New intraocular pressure measurement method using reflected pneumatic pressure from cornea deformed by air puff of ring-type nozzle

A Threshold based Algorithm to Detect Peripapillary Atrophy for Glaucoma Diagnosis

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