DIS - Angle Closure Glaucoma II - Week 5 Flashcards
List three mechanisms of angle closure.
Plateau iris
Pupil block
Posterior pressure
Describe plateau iris. What happens on dilation? Give the clinical definition of plateau iris.
Caused by the anterior insertion of the iris into the ciliary body
Produces iris bunching in the angle on dilation
Closed angle on gonioscopy/OCT with a flat iris and normal AC depth
What technique often fails with plateau iris?
Peripheral laser iridotomy
Where does the ciliary body extend to in plateau iris and what does it support? What does it result in when indenting on gonioscopy?
The ciliary body extends under the iris, supports the far peripheral iris to give a double hump on indentation
Describe the mechanism of AC crowding and how it differs to plateau iris. Describe what the choroid does.
Similar to plateau iris but the iris root is in a normal position
The cause of crowding is a ciliary body twist, rotating the iris about its scleral anchor
It twists further as the choroid pushes it further
What is a major cause of angle closure in asian eyes?
AC crowding
List a cause of AC crowding (not the mechanism).
Choroidal effusion causes the uvea to elongate anf the ciliary body to rotate forward with the scleral spur as the hinge
New location of the ciliary body is under the iris root
Is choroidal effusion common in asian eyes with angle closure glaucoma or is it rare?
Common
Describe pupil touch, why it happens (2), and its effect on IOP, if any. Note if this is normal or abnormal. Also note what happens in most cases.
Occurs whn the iris and lens make contact at the pupil margin
Happens due to lens growth with age, or due to forward lens placement (lens vault)
Pupil touch elevates IOP in the posterior chamber - normal ageing process
In most cases, increased posterior IOP will lift the iris off to re-establish flow under the iris
Describe pupil block and what it is due to (2).
Requires iris touch and occurs due to muscle forces and age related loss of iris tissue tone
Describe quigleys mechanism for how pupil block occurs (4). Explain what happens with miosis/mydriasis and if there is any angle block.
Iris muscles were slackest in mid dilation, when both iris muscles are fully relaxed
This gives greatest sphincter vector force onto the lens to block aqueous
Slack iris tissue would be more likely to form a forward bow
The dilator would pull this slack tissue into the angle, obstructing the TM
Miosis - sphincter tension keeps iris tight - no block
Mydriasis - dilator keeps iris tight - no block
Mid-dilation - block
Describe what is meant by asian paradox for angle closure.
Asian eyes have similar anterior chamber depth to everyone else, but still get more primary angle closure than everyone else
Do both pupil block and AC crowding collectively explain the asian paradox?
Yes
Describe the corneal wedge for gonioscopy, including what you look for and setup.
Wedge defines the corneal limbus and the start of the angle
Offset the slit 30-45 and use a narrow beam
Look for reflections in the corneal epithelium and endothelium
Where they meet is schwalbes line
What can you do when PTM is not visible on gonioscopy?
Indentation
