This site is intended for healthcare professionals

Go to /sign-in page

You can view 5 more pages before signing in

Investigations

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

The angle formed by the iris and cornea is normally hidden from direct observation by the overlapping of the sclera at the limbus. The angle may be viewed microscopically once the refraction of the cornea is cancelled by applying a dome-shaped contact lens - for a hand-held microscope - or a Goldmann lens - for a slit-lamp microscope.

In an open angle, the end of Descemet's membrane in the cornea appears as a pale line marking the anterior insertion of the trabeculae. In a narrow angle, only Schwalbe's line and a glimpse of the trabeculae are visible. In a wide angle, the root of the ciliary body may be seen.

Many techniques enable measurement of intra-ocular pressure. The three most popular ones are:

  • Goldmann applanation tonometer - requires topical anaesthesia and fluorescein but has a high level of accuracy. The force required to flatten a small area of cornea is measured by a prism fitted to a tonometer.
  • "air-puff" tonometer - the cornea is flattened using a small puff of air. The procedure does not require anaesthesia but is not very accurate.
  • Schiotz tonometer - the weight required to indent the cornea is measured and converted to a pressure value. It requires topical anaesthesia but is portable.

NICE suggest that with respect to the diagnosis of chronic open angle glaucoma (COAG):

  • at diagnosis offer all people who have COAG, who are suspected of having COAG or who have OHT all of the following tests:
    • visual field assessment using standard automated perimetry (central thresholding test), repeated if necessary to establish severity at diagnosis
    • optic nerve assessment and fundus examination using stereoscopic slit lamp biomicroscopy, with pupil dilatation
    • IOP measurement using Goldmann applanation tonometry (slit lamp mounted)
    • peripheral anterior chamber configuration and depth assessments using gonioscopy
    • central corneal thickness (CCT) measurement

Notes:

  • intraocular pressure (IOP) measurement using Goldmann applanation tonometry (slit lamp mounted)
    • actual value > 21mmHg
      • artefactually high IOP levels are seen in greater central corneal thickness
      • artefactually low IOP levels are seen in lesser central corneal thickness
    • diurnal variation in IOP is greater than 4 mmHg (2)

Reference:


Create an account to add page annotations

Annotations allow you to add information to this page that would be handy to have on hand during a consultation. E.g. a website or number. This information will always show when you visit this page.

The content herein is provided for informational purposes and does not replace the need to apply professional clinical judgement when diagnosing or treating any medical condition. A licensed medical practitioner should be consulted for diagnosis and treatment of any and all medical conditions.

Connect

Copyright 2024 Oxbridge Solutions Limited, a subsidiary of OmniaMed Communications Limited. All rights reserved. Any distribution or duplication of the information contained herein is strictly prohibited. Oxbridge Solutions receives funding from advertising but maintains editorial independence.