For more information on this topic, please listen to the podcast episode that Dr Foster and I recorded for my Talking About Glaucoma series. The link will be updated once the podcast is edited; for now, check out all my episodes of ‘Talking About Glaucoma’ on iTunes.
26Jun2010 1100hrs presented at the COS Annual Meeting in Quebec City by Mr Paul Foster from Moorfields Eye Hospital (designation in the UK is such that Mr is the term for full consultant as opposed to Dr Foster begins by reviewing the same 2010 and 2020 prevalence data and the current classification system:
- 3x as many POAG vs PACG but if look at the incidence of blindness, the prevalence is equal so PACG more likely to blind.
- 11-27% POAG vs 33-75% blindness prevalence south east asia
- Incidence of AACG reported higher in East Asian communities and only about 1/3rd angle closure glaucoma presenting with acute attack
- Traditional classification does not focus on disc damage, just on course of the IOP rise
- Classification moving to more objective measure with natural history staging and the mechanism responsible for the disease
- Natural history Suspects—>Angle closure—>ACG
The Trabecular Meshwork (TM) in ACG is interesting to look at during different stages eg disruption of TM beams after acute attack. But, looking at specimens in patients who never had an acute attack, damage in TM is evident in areas away from the PAS. (Which actually happens first?)
Mechanisms: Synechial, Appositional, TM damage all increase risk of glaucomatous optic neuropathy
Schaffer classification revisited ie 40 deg angle never close vs 20 deg or less increase risk
- <1% population has PAS if angle 30-40 deg
- 8-12% if angle 20 deg
- Further increase PAS when narrower still
- The way you asses the angle can make a huge difference ie lights on vs off (and how much light you shine through the pupil)
- Women > Men asia
- Axial length shorter results in AC depth and volume reduction, radio us of cornea, thickness of lens and lens position
- Therefore anatomical risk factor of shallow AC biggest risk
- Sympathomimetics, Anticholinergics, Idiosyncratic (anti-histamines, etc), stress/anxiety, climate, lighting, posture
- Myocilin looked at in China and NOT found to be associated with ACG
- Weill-Marchesani, Marfan and Ehler-Danlos likely from zonular laxity
- RP and perhaps Best Maculopathy
Q: Mentions speaker’s study of cataract extraction reducing angle closure; does this apply to caucasians
A: yes, similar studies showing lower rates new angle closure in patients who had cataract surgery
Therefore, quoting Ravi Thomas’ ENT approach, if you smell a cataract in ACG patient, take it out as long as visually significant but should we consider ever if not visually significant
Q: What about second generation Asian patients, do these associations drop?
A; The biometrics are changing, particularly in Chinese populations. The rate of myopia has been steadily climbing in Taiwanese, now at 92%. Similarly in Singapore.
Australian Chinese much less myopic and maybe related to much more time spent outdoors