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Case Reports and Images in Medicine

 
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Clinical Image
 
24-hour intraocular pressure measurement in glaucoma
Iain Davidson1, Katie Hoban2, Andrew J. Tatham2
1Plymouth University, Peninsula College of Medicine and Dentistry, Plymouth, UK.
2Princess Alexandra Eye Pavilion and Department of Ophthalmology, University of Edinburgh, Edinburgh, UK.

Article ID: 100026Z09ID2016
doi:10.5348/Z09-2016-26-CL-19

Address correspondence to:
Andrew J. Tatham
Princess Alexandra Eye Pavilion
45 Chalmers Street
Edinburgh EH3 9HA

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Davidson I, Hoban K, Tatham AJ. 24-hour intraocular pressure measurement in glaucoma. J Case Rep Images Med 2016;2:83–85.



Case Report

A 62-year-old female with normal tension glaucoma presented with progressive visual field loss in the right eye. Her intraocular pressure (IOP) measured 15 mmHg using Goldmann applanation tonometry and IOP had been at similar consistently low levels at previous visits during office hours.

24-hour contact lens sensor recording was performed on the right eye using the "Triggerfish" CLS (SENSIMED Inc., Switzerland), a new FDA approved telemetric sensor that allows wireless monitoring of diurnal changes in ocular dimension related to changes in IOP [1] . The contact lens sensor contains strain gauges that convert ocular dimensional changes into electrical signals (expressed in mV). Measurements were recorded for 30 seconds every 5 minutes for a full 24-hour period of normal activities. Data was transmitted wirelessly from the contact lens sensor to an antennae taped to the patients' head and stored in a portable device worn around the neck. After 24 hours the contact lens sensor was removed and data was downloaded and analyzed. Using conventional tonometry, IOP was 15 mmHg immediately prior to contact lens sensor insertion and 15 mmHg on removal of the device 24 hours later. However, the contact lens sensor revealed a large amplitude of diurnal variation between visits, with a peak measurement at 7 a.m. and trough at 6 p.m. (Figure 1A). The contact lens sensor automatically identified the sleeping period by analyzing blink patterns, with blinks producing a transient spike in the electrical signal. A contact lens sensor recording for a patient with no significant diurnal variation is shown in Figure 1B for comparison.

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Figure 1: Contact lens sensor recording showing ocular dimensional changes over 24 hours in the 62-year-old patient with progressive glaucoma (A) The sleeping period was automatically identified by the CLS and is shown by the grey bars. (B) A contact lens sensor recording in a patient who had no significant fluctuation in measurements over 24 hours (B).


Discussion

Glaucoma, the most common cause of irreversible blindness, is an optic neuropathy characterized by progressive loss of retinal ganglion cells and accompanying loss of visual field. The major risk factor for glaucoma is raised IOP, however, many patients develop glaucoma or continue to lose vision, despite seemingly low IOP [2]. Measurement of IOP is typically restricted to office hours, but as IOP is subject to diurnal variation, many patients may have undetected high pressure. In fact, sleep laboratory studies have shown over 75% of people have a peak IOP during nocturnal hours [3].

Contact lens sensors offer the possibility of 24 hours IOP monitoring, with the potential to be used to determine timings of peak IOP and patterns of IOP variation without the expense and inconvenience of a sleep laboratory. Contact lens sensors also have the advantage of not needing to wake the patient or sit them up to obtain measurements, movements that themselves might influence pressure measurements.

Although it is still not certain whether IOP fluctuation is a risk factor for progressive visual loss in glaucoma, a recent study found eyes with higher amplitude fluctuations in IOP had faster rates of historical visual field deterioration [4]. Therefore, knowledge of magnitude of IOP fluctuations may allow better prediction of risk of visual loss and evaluation of treatment efficacy. The contact lens sensor may also help determine the most important time of day to measure IOP and capture peak levels [1]. This may allow the timing of medications to be individualized, particularly as sleep studies have shown some common anti-glaucoma medications such as beta-blockers are not effective over 24 hours [3].


Conclusion

The successful management of glaucoma depends on lowering IOP, however, conventional methods of measuring IOP are limited as they allow only infrequent office hour readings. We used a contact lens sensor to obtain measurements over 24 hours in a patient with progressive glaucoma. Although the patient had consistently low IOP during the daytime, the contact lens sensor suggested a peak IOP during the early hours. Further studies are needed to determine whether the fluctuations detected using the contact lens sensor indicate higher risk of disease progression.

Keywords: Contact lens, Glaucoma, Intraocular pressure, Visual field


References
  1. Liu JH, Mansouri K, Weinreb RN. Estimation of 24-Hour Intraocular Pressure Peak Timing and Variation Using a Contact Lens Sensor. PLoS One 2015 Jun 15;10(6):e0129529.   [CrossRef]   [Pubmed]    Back to citation no. 1
  2. Weinreb RN, Aung T, Medeiros FA. The pathophysiology and treatment of glaucoma: A review. JAMA 2014 May 14;311(18):1901–11.   [CrossRef]   [Pubmed]    Back to citation no. 2
  3. Mansouri K, Weinreb RN, Medeiros FA. Is 24-hour intraocular pressure monitoring necessary in glaucoma? Semin Ophthalmol 2013 May;28(3):157–64.   [CrossRef]   [Pubmed]    Back to citation no. 3
  4. De Moraes CG, Jasien JV, Simon-Zoula S, Liebmann JM, Ritch R. Visual Field Change and 24-Hour IOP-Related Profile with a Contact Lens Sensor in Treated Glaucoma Patients. Ophthalmology 2016 Apr;123(4):744–53.   [CrossRef]   [Pubmed]    Back to citation no. 4
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Author Contributions
Iain Davidson – Substantial contributions to conception and design, Acquisition of data, Analysis and interpretation of data, Drafting the article, Revising it critically for important intellectual content, Final approval of the version to be published
Katie Hoban – Substantial contributions to conception and design, Acquisition of data, Analysis and interpretation of data, Drafting the article, Revising it critically for important intellectual content, Final approval of the version to be published
Andrew J. Tatham – Substantial contributions to conception and design, Acquisition of data, Analysis and interpretation of data, Drafting the article, Revising it critically for important intellectual content, Final approval of the version to be published
Guarantor of submission
The corresponding author is the guarantor of submission.
Source of support
None
Conflict of interest
Authors declare no conflict of interest.
Copyright
© 2016 Iain Davidson et al. This article is distributed under the terms of Creative Commons Attribution License which permits unrestricted use, distribution and reproduction in any medium provided the original author(s) and original publisher are properly credited. Please see the copyright policy on the journal website for more information.



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