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Editors Selection IGR 23-1

IOP, VF, Imaging and Electrophysiology: IOP in upgaze

Comment by Rupert Bourne on:

22344 Is gaze-dependent tonometry a useful tool in the differential diagnosis of Graves' ophthalmopathy?, Herzog D; Hoffmann R; Schmidtmann I et al., Graefe's Archive for Clinical and Experimental Ophthalmology, 2008; 246: 1737-1741

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Opinion can be divided on the merits of using the finding of a rise in intraocular pressure on upgaze as a 'diagnostic sign' of Grave's ophthalmopathy (GO). This study by Herzog et al. (1421) investigated this 'sign' by comparing intraocular pressure on upgaze between healthy volunteers and GO patients with varying degrees of motility restriction. To address the concern that rise in IOP on upgaze may be the result of a measurement error due to non-central placement of the tonometer head, the authors thoughtfully adapted the slit-lamp chin rest to incline the head resulting in 20° upgaze which enabled applanation of central cornea. The study confirmed that a significant rise in IOP does occur in upgaze in patients with GO, but that this rise is considerably smaller when taking central corneal measurements on upgaze.

A significant rise in IOP does occur in upgaze in patients with Grave's ophthalmopathy. This rise is considerably smaller when taking central corneal measurements on upgaze

Reasons for this include applanation of thicker peripheral cornea and raised orbicularis muscle tone due to sustained eyelid opening in conventional upgaze measurements. Interestingly, the IOP of normal subjects also rose by up to 11 mmHg using conventional upgaze tonometry. The ROC curves they report show that with both forms of upgaze IOP measurement (conventional or head inclined), the power to discriminate between normal subjects and GO patients was relatively poor (conventional upgaze, AUC = 0.67; head inclination upgaze, AUC = 0.65) with low sensitivity (18% when using a 3-mmHg mean difference of IOP between primary and upgaze position). There are some minor concerns regarding the methodology, such as not randomizing the order in which the measurements were taken, and the authors also do not address the issue that the tonometer head of GO eyes with poor motility will rest in a different place to those with better motility, however, their conclusion that the 'diagnostic' value of this sign in evaluation of GO patients is weak appears justified.

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