This talk dealt with the current epidemiological data on primary open angle glaucoma (POAG) including descriptive, prevalence, and incidence data, as well as the analytics, the WHY, including risk factors for incidence and progression. There is variability in definitions of glaucoma, including optic disc structural damage and visual field +/- IOP.
Putting glaucoma into perspective with other causes of blindness in the world:
- Cataract makes up almost half world blindness with glaucoma second at 12% and AMD 9%
- Different other populations eg african descent with glaucoma top cause at 33%
- European white in comparison, glaucoma only 6%
- Barbados study 9 yr blindness 1/5 due to glaucoma
- Worldwide 45M in 2010, set 59M in 2020 glaucoma
- Still, half not previously diagnosed and half had IOPs below those set for screening in the study, large ancestral differences
Dr Leske mentioned the Los Angeles Latino Eye Study and others and meta-analysis studies and points out that these were all prevalence and not incidence reports. Incidence studies have very small patient numbers and few studies done looking at new glaucoma developing over time as patients are being followed. We also know the natural history of glaucoma is a continuum ranging from undetectable to asymptomatic to functional impairment
To further confuse matters, we are not always clear in stating what are risk factors for ending up with glaucoma vs factors increasing the risk of progression of established disease. (Perhaps since the disease is a continuum, some of these factors do overlap.) Risk factors include:
- Demographic factors: age is critical, likelihood increases from 1.6-2.0 per 10 years of age
- Ancestory eg west african and mexican higher
- Sex: higher for men than for women?
- Familial: increase in family members
- Various genetic studies: but genes identified have not been terribly revealing as very low impact eg just for certain families and little to explain the common garden variety
- Very complex inheritance; greatest yield may be gene/environment interactions
- Systemic factors: diabetes very variable; vascular - vasospasm, BP assoc’d with IOP but hard to link with glaucoma, low diastolic perfusion pressure consistently associated
- Ocular risk factors: large optic discs, myopia, thin CCT, high IOP (Barbados)
More details regarding intra-ocular pressure (IOP):
- Large overlap though of IOP curves of those developing glaucoma vs not in the 9 years of the Barbados study so on a population based analysis, IOP little predictive factor for development of glaucoma
- Therefore, little evidence to support value of IOP as screening tool
- However, meta analysis showing decreased relative risk conversion to OAG by 14% w/ each mmHg IOP reduction but NNT is between 12-20 to prevent one conversion
Early Manifest Glaucoma Trial (EMGT) Overview
(Dr Leske was the chair of the data centre for this landmark trial. Links to the publications are posted at the NEI.)
This trial examined the value of IOP lowering in early glaucoma randomizing to just ALT and betaxolol vs no treatment to reach a 25% reduction in IOP. Visual Field loss averaged -0.40 dB/yr control patients but there was a lot of variability. Loss was greater with Pseudoexfoliation Glaucoma (PXFG) and higher with IOP >=21 vs <21. Mean time to progression was 42.8 months (in the control group) and this served as a good natural history study since this group received no treatment and was allowed to progress.
Progression risk factors:
- higher mean IOP?
- older age females?
- optic disc size/change
- Worse VF/MD - not all
- Disc heme/PXF
- Many other factors yet to be confirmed
Overall, progression goes very slowly but the older the age and larger the VF defect at presentation and non-adherence to Tx, the more likely the chance of progression.
- Epidemiology has made contributions
- Need for early detection
- Disease course still highly variable based on predictive factors
- Standardized criteria for definitions
- Multifactorial etiology
- Early identification
- Screening methods and cost effectiveness
Discussion period followed
Q: have we decreased the progression of glaucoma in west indes since the barbados study
A: We wold hope so but have not done a study
Q: Difference ancestral origins of differing black populations; did certain families settling in certain countries influence the prevalence
A: a factor but also wide variation
Q: IOP fluctuation not proven risk factor but PXF higher risk progress; is this independent of IOP?
A: Yes, indeed, independent risk factor at an unbelievable higher rate than others with IOP >=21