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Intraocular pressure: clinical aspects and new measurement methods
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Ophthalmology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Intraocular pressure (IOP) measurement is a routine procedure and a fundament in glaucoma care. Elevated IOP is the main risk factor for glaucoma, and to date, reduction of IOP is the only possible treatment.

In a retrospective clinical material, the prevalence of open angle glaucoma was estimated on the west coast of Iceland. IOP measurement and optic nerve head examination were used to capture glaucoma suspects, within the compulsory ophthalmological examination for the prescription of eye glasses. The results were mainly in agreement with a recent prospective study in the same region. This indicated that retrospective data, under certain conditions, may contribute with useful information on the prevalence of glaucoma. However, normal tension glaucoma is underestimated if perimetry and/or fundus photography are not included in the examination.

Three studies focused on the measurement of IOP. Goldmann applanation tonometry (GAT) is the standard method. GAT is affected by corneal properties, e.g. central corneal thickness (CCT) and corneal curvature (CC). Refractive surgery changes these properties. This has put focus on how corneal biomechanics translate into tonometric errors and stimulated the development of new methods. As a result, Pascal

® Dynamic Contour Tonometry (PDCT) and Icare® rebound tonometry have been introduced. A method under development by our research group is Applanation Resonance Tonometry (ART). It is based on resonance technology and estimates IOP from continuous measurement of force and contact area.

Comparison of PDCT, Icare and GAT in a prospective study showed that the concordance to GAT was close to the limits set by the International Standard Organization (ISO) for PDCT, while Icare was outside the limits.

To investigate if laser-assisted subepithelial keratectomy (LASEK) affects tonometry, a study was performed where measurements with GAT, PDCT and ART were obtained before, three and six months after LASEK. The hypothesis was that PDCT and ART would be less affected by LASEK than GAT. The results showed a statistically significant reduction of measured IOP three and six months after LASEK for all tonometry methods. Change in visual acuity and IOP between three and six months suggested a prolonged postoperative process.

A servo-controlled prototype (ART

servo) was developed. A study was undertaken to assess the agreement of ARTservo and a further developed v

manual prototype (ART

manual) with GAT. The study design was in accordance with the requirements of the ISO standard for tonometers. ARTmanual fulfilled the precision requirements of the ISO standard. ARTservo did not meet all the requirements of the standard at the highest pressure levels.

Four tonometry methods, GAT, PDCT, Icare and ART, were investigated. None of them was independent of both CCT and CC. The inconsistencies in the results emphasize the importance of study design. A meta-analysis comprising healthy eyes (IOP ≤ 21 mmHg) in the three papers, revealed age as an important confounder.

In summary, glaucoma prevalence in Iceland was investigated and the results indicated that a retrospective approach can contribute with meaningful information. ART and PDCT had a similar agreement to GAT. ART

manual fulfilled the precision requirements set by the ISO-standard, ARTservo and PDCT were close, while Icare was distinctly outside the limits. All tonometry methods were affected by LASEK and no method was completely independent of corneal properties.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2011. , 44 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1395
Keyword [en]
Intraocular pressure, glaucoma, tonometry, ISO, LASEK, CCT, curvature
National Category
Ophthalmology
Research subject
Ophtalmology
Identifiers
URN: urn:nbn:se:umu:diva-40383ISBN: 978-91-7459-132-3 (print)OAI: oai:DiVA.org:umu-40383DiVA: diva2:399503
Public defence
2011-03-18, Bergasalen, Norrlands universitetssjukhus, Umeå, 14:04 (Swedish)
Opponent
Supervisors
Available from: 2011-02-25 Created: 2011-02-22 Last updated: 2011-02-25Bibliographically approved
List of papers
1. Can the prevalence of open-angle glaucoma be estimated from a retrospective clinical material? A study on the west coast of Iceland.
Open this publication in new window or tab >>Can the prevalence of open-angle glaucoma be estimated from a retrospective clinical material? A study on the west coast of Iceland.
2005 (English)In: Acta Ophthalmologica Scandinavica, ISSN 1395-3907, E-ISSN 1600-0420, Vol. 83, no 5, 549-553 p.Article in journal (Refereed) Published
Abstract [en]

PURPOSE: To explore the possibility of estimating the prevalence of open-angle glaucoma (OAG) on the west coast of Iceland using a clinical retrospective material, and to compare that estimate with the results from a recent prospective Icelandic study.

METHODS: The compulsory ophthalmological examination for the prescription of eye glasses in combination with information obtained from Statistics Iceland were used to establish the prevalence of glaucoma in Akranes and to estimate the minimum prevalence for the greater west coast area. A recent prospective study from Iceland was used as reference.

RESULTS: In all, 79% of 1443 Akranes inhabitants aged 50 years or more had visited the eye clinic at least once between 1996 and 2001. The prevalence of OAG was 4.8% (95% CI 3.6-6.1). The minimum prevalence for the west coast was 3.8% (95% CI 3.2-4.4). The prevalence increased with age (p < 0.001). The overall prevalence was similar to that of recently published prospective data but the prevalence of normal tension glaucoma (NTG) was lower.

CONCLUSION: The results from the two studies are similar in many respects, which indicates that retrospective data may supply meaningful information on glaucoma prevalence. Important sources of error are the selection and attendance of patients, screening methods and diagnostic criteria. If routine examination does not include fundus photography and/or perimetry, the prevalence of NTG will be underestimated.

Keyword
applanation resonance tonometry, glaucoma, IOP
National Category
Ophthalmology
Research subject
Ophtalmology
Identifiers
urn:nbn:se:umu:diva-34205 (URN)10.1111/j.1600-0420.2005.00514.x (DOI)16187991 (PubMedID)744 (Local ID)744 (Archive number)744 (OAI)
Available from: 2010-05-20 Created: 2010-05-20 Last updated: 2017-12-12Bibliographically approved
2. Pascal, ICare and Goldmann applanation tonometry: a comparative study
Open this publication in new window or tab >>Pascal, ICare and Goldmann applanation tonometry: a comparative study
2008 (English)In: Acta ophthalmologica, ISSN 1755-3768, Vol. 86, no 6, 614-621 p.Article in journal (Refereed) Published
Abstract [en]

PURPOSE: To compare intraocular pressure (IOP) measurements by Pascal, ICare and Goldmann applanation tonometry (GAT), to evaluate the effects of central corneal thickness (CCT) and curvature on IOP measurement and to estimate the intra-observer variability.

METHODS: A prospective, single-centre study of 150 eyes with a wide range of pressures. Six masked IOP measurements/method; corneal thickness and curvature were studied for each eye. GAT was the reference.

RESULTS: IOPPascal and IOPICare correlated with IOPGAT (r = 0.91, 0.89). Mean ICare measurement exceeded GAT by 2 mmHg. Pascal measured higher than GAT at low IOPs and lower at high IOPs. For every 10 mmHg increase in IOP above 31 mmHg, Pascal measured 2 mmHg lower than GAT and vice versa. CCT was correlated significantly with IOPGAT (r = 0.23) and IOPICare (r = 0.43) but not with IOPPascal (P = 0.12). CCT was correlated with age. In a subgroup (>50 years), ICare and the difference between IOPGAT and IOPPascal were affected significantly by the CCT, whereas IOPGAT and IOPPascal were not. Corneal curvature was correlated significantly with IOPGAT (r = -0.27) and IOPPascal (r = -0.26) but not with IOPICare (P = 0.60). Intra-observer variability within each set of six measurements was approximately 2 mmHg, irrespective of method.

CONCLUSION: This study showed a reasonable overall correlation and concordance between the IOP obtained with the three instruments. None of the methods were completely independent of the biomechanical properties of the cornea. ICare showed a significant dependency upon CCT, whereas GAT and Pascal showed a significant dependency on corneal curvature. All methods showed intra-observer variability, which leaves room for further improvement of methods.

Keyword
CCT; corneal curvature; dynamic contour tonometry; Goldmann; ICare; intraocular pressure; Pascal; rebound tonometry; tonometry
National Category
Ophthalmology
Research subject
Ophtalmology
Identifiers
urn:nbn:se:umu:diva-23745 (URN)10.1111/j.1600-0420.2007.01112.x (DOI)18093261 (PubMedID)744 (Local ID)744 (Archive number)744 (OAI)
Available from: 2009-06-29 Created: 2009-06-29 Last updated: 2016-04-27Bibliographically approved
3. Change in intraocular pressure measurement after myopic LASEK: a study evaluating Goldmann, Pascal and applanation resonance tonometry
Open this publication in new window or tab >>Change in intraocular pressure measurement after myopic LASEK: a study evaluating Goldmann, Pascal and applanation resonance tonometry
Show others...
(English)Article in journal (Refereed) Accepted
Identifiers
urn:nbn:se:umu:diva-40380 (URN)
Available from: 2011-02-22 Created: 2011-02-22 Last updated: 2011-02-25Bibliographically approved
4. Introduction and clinical evaluation of servo-controlled applanation resonance tonometry
Open this publication in new window or tab >>Introduction and clinical evaluation of servo-controlled applanation resonance tonometry
2012 (English)In: Acta Ophthalmologica Scandinavica, ISSN 1395-3907, E-ISSN 1600-0420, Vol. 90, no 7, 677-682 p.Article in journal (Refereed) Published
Abstract [en]

Purpose:  In recent years, Applanation Resonance Tonometry (ART) has been suggested for intraocular pressure (IOP) measurements. The manual version of ART (ARTmanual) has been further developed, and to improve usability, an automatic servo-controlled prototype (ARTservo) has been proposed. The aim of this study was to assess the limits of agreement (LoA) of ARTmanual and ARTservo as compared with the reference method, Goldmann Applanation Tonometry (GAT).

Methods:  This was a prospective single-centre study on 152 eyes from 77 subjects. It was designed according to International Standard Organization’s (ISO) requirements for tonometers (ISO 2001). Intraocular pressure was measured six times/method in a standardized order. The ART technique has two available analysis procedures: a dynamic one that measures IOP during the indentation phase and a static one that causes a Goldmann-like measurement during two seconds of full applanation. The 95% LoA was defined as ±1.96 × standard deviation of difference against GAT.

Results:  Mean IOP for GAT was 19.1 mmHg (range: 10–37 mmHg). The 95% LoA of ARTmanual was ±4.5 mmHg for both dynamic and static analyses. The 95% LoA of ARTservo was ±5.7 mmHg for dynamic and ±4.9 mmHg for static analyses.

Conclusions:  This study confirms that the ART methodology is feasible. The further developed ARTmanual fulfilled the ISO standard with both the dynamic and the static analysis techniques. ARTservo with static analysis was close to fulfilling the standard but failed to do so in the highest IOP range. ARTservo has the potential to greatly improve usability if further development is completed.

Keyword
applanation resonance tonometry, ART, glaucoma, intraocular pressure, ISO standard, tonometry
National Category
Ophthalmology
Research subject
Ophtalmology
Identifiers
urn:nbn:se:umu:diva-40382 (URN)10.1111/j.1755-3768.2011.02111.x (DOI)000310548500026 ()
Note

Kompletteras 2012-09

Available from: 2011-02-22 Created: 2011-02-22 Last updated: 2017-12-11Bibliographically approved

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