Introduction
Based on empirical data and also from studies from
individual countries in the Caribbean,
primary open angle glaucoma (POAG) is the
most common form of glaucoma in the Caribbean region.
Studies of black West Indian
populations in St. Lucia and
Barbados show a prevalence of
8.8% and 6.6%, respectively.1,2
It is the most common form of
glaucoma in the US (approx .
1.86% in adults over 40 years).3
1. Mason RP,et al. National survey of the prevalence and risk factors of glaucoma in St. Lucia, West Indies. Part I. Ophthalmology. 1989 Sep;96(9):1363-8.
2. Leske MC, et al. The Barbados Eye Study. Prevalence of open angle glaucoma. Arch Ophthalmol. 1994 Jun;112(6):821-9.
3. Friedman DS, et al; Prevalence of open-angle glaucoma among adults in the United States. Arch Ophthalmol. 2004 Apr;122(4):532-8.
Most literature contend that
POAG varies significantly
according to race and ethnicity.
In Caucasians > 40 years in the
US, the prevalence is 1.69%.3
The Baltimore Eye Study concluded that OAG is three times
more prevalent among African Americans in the United
States than among Caucasians.4
In the Latino population in the US prevalence ranges from
1.97%5 and 4.89%6,7 in Latino adults over the age of 40.5
Studies in other ethnic groups show a higher prevalence.
3. Friedman DS, et al; Prevalence of open-angle glaucoma among adults in the United States. Arch Ophthalmol. 2004 Apr;122(4):532-8.
4. Tielsch JM, Sommer A, Katz J. Racial variations in the prevalence of openangle glaucoma. The Baltimore eye survey. JAMA 1991; 266:369 – 74.
5. Quigley HA, et al. The prevalence of glaucoma in a population-based study of Hispanic subjects. Arch Ophthalmol. 2001 Dec;119(12):1819-26.
6. Varma R, et al; Los Angeles Latino Eye Study Group. Prevalence of OAG and ocular hypertension in Latinos. Ophthalmology. 2004 Aug;111(8):1439-48.
7. Kim E, Varma R. Glaucoma in Latinos/Hispanics. Curr Opin Ophthalmol. 2010 Mar;21(2):100-5.
American Indian/Alaskan Native populations also show
a large percentage of normal-tension glaucoma with a 6.2%
prevalence of OAG, 100% of which had normal eye pressures.10
It is accepted that people of Asian descent are much more
likely to suffer from angle
closure glaucoma (ACG),
while those of African or
European origin are more
likely to develop POAG.
Despite this, population
based studies in India
report prevalences of
POAG between 2 to 13%.*
*(Vellore Eye Survey, Andhra Pradesh Eye Disease Study, Aravind Comprehensive Eye Survey, Chennai Glaucoma Study and
West Bengal Glaucoma Study).
Primary open angle glaucoma is estimated to affect
6.48 million persons whilst primary angle-closure glaucoma
is estimated at 2.54 million.
Most of those with disease are undetected and major
challenges exist in detecting and treating those with disease.
In addition, the Ocular Hypertension Treatment Study
(OHTS) showed that black race was a risk factor for
conversion from ocular hypertension
to OAG.10 However, it also showed that
corneal thickness and cup-to-disc ratio
may present a better means of
evaluating risk factors than race.
10. Sommer A, Tielsch JM, Katz J et al. Racial differences in the cause-specific prevalence of blindness in East Baltimore. NEJM 1991; 325:1412-1417.
Brief Review of Glaucoma – Key Points
Brief Review of Glaucoma – Key Points
Brief Review of Glaucoma – Key Points
• Glaucoma
- Characteristic visual loss from optic neuropathy
- Open angle (Chronic); Closed angle (Acute)
- Usually  IOP (also vascular mechanism)
Brief Review of Glaucoma – Key Points
• Treatment slows progression
• Drug Rx:
All are directed towardsIOP either via:
-  aqueous production
beta-blockers, alpha-2 agonists,
carbonic anhydrase inhibitors
-  aqueous outflow
prostaglandins, adrenergic agonists,
parasympathomimetics
• Non-pharmacologic ways to lower IOP:
- Laser (argon laser trabeculoplasty, PI for ACG)
- Surgical (trabeculectomy, tubes, valves and shunts)
Guyana Situation
In Guyana, our two major ethnic groups
are of Indian origin and African origin.
Minorities include Portuguese, Chinese,
Indigenous and mixed groups.
Hence, in assuming the prevalence risks
for Glaucoma in our country, looking at
data from studies with similar ethnicity
gives us an idea of what the dimension is like.
In 2009, a random sampling and analysis of data from records
at Georgetown Public Hospital showed that 9% of patients
presenting to the Eye Clinic were likely to have a diagnosis
of OAG with majority of patients being of African ethnicity.
Diagnosis
Diagnosis is straightforward in
advanced cases with all the
characteristic features.
In Guyana, these cases are easily
diagnosed by all levels of eye care
personnel and are immediately
treated or referred for treatment.
Diagnosis becomes more technical
in early glaucoma cases or in normal
tension cases.
These patients usually are in their late 30s and early 40s.
Due to lack of sophisticated testing methods
(such as OCT, HRTs, Blue-Yellow HVF), diagnosis is usually
based on clinical judgement in these early cases.
In present day, there are eye care personnel that manage
and treat glaucoma cases diagnosed based purely on cupdisc ratios.
Tonometry and measuring of IOP
is now an accepted mode of
management here in Guyana.
Majority of eye-care practioners use pneumotonometry
since it is convenient and easily done.
A few centres do use applanation tonometry (such as
Goldmann and Perkin’s Tonometry) which is the gold
standard worldwide.
Applanation tonometry has its disadvantage in that it needs
special skill and experience, combined with the regular
supply of fluorescein and topical anaesthesia.
Modern developments and research on glaucoma has now
enabled us to go beyond this where we need also to consider
other factors such as characteristics of
the neuro-retinal rim, size of the optic
nerve and the central corneal thickness
(pachymetry). Only two centres in
Guyana offer pachymetry.
The use of Humphrey’s Visual
Field (HVF) as a diagnostic tool
needs to be carefully done by
those trained in interpreting
these fields.
Patients are being given glaucoma
treatment based on visual fields that
aren’t correlated with the optic disc
findings.
The follow-up of patients progress
using HVF along with tonometry and
optic disc evaluation are the present modes available.
POAG in Guyana
In Guyana, POAG in the
Afro-Guyanese population
present usually with very
advanced features and with
patients already having a
tremendous loss of vision.
This finding is common in both old and young age group.
Quite a few of these patients presenting to our clinic are
previously undiagnosed cases. This presents a challenge
because patients with advanced vision loss are risk for
further loss of vision if surgical intervention is needed.
The usual approach is to try to initiate or maximise their
topical glaucoma medications until maximum tolerated
medical therapy is achieved.
It is especially difficult to
convince younger patients
with advanced field loss
(tunnel vision) with 20/20
central vision, to undergo
surgery.
Typical profile for these patients are high IOPs, deep
excavated cups with thin rims and C:D ratios – usually > 0.7.
50% of times there is a positive family history, but this may
be higher due to undiagnosed cases in the family.
Screening of relatives is usually recommended.
NTG in Guyana
Normal tension glaucoma seems to be more common in
Indo-Guyanese patients who are also prone to diabetes.
These patients present in various stages from early disease
to advanced disease.
Their IOPs range from 10-14mmHg. The younger patients
usually have borderline IOPs 18-20mmHg which might be
influenced by CCT and hence they can very well be POAG
cases.
Most NTG cases are initialised
on topical glaucoma eye drops
and their IOPs and Visual Fields
are monitored for effectiveness
of treatment.
HVF measurement is found to
be highly unreliable across the
population usually due to difficulty
in interpreting the instructions during the test.
Also in elderly patients, apart from comprehending the
instructions, response time affects their ability to give
reliable readings. There, we can only rely on clinical
judgement along with IOPs as our guide for treatment.
ACG in Guyana
A few cases of Primary Angle Closure Glaucoma exist and they
are commoner in the indigenous (Amerindian) population.
Otherwise a few have been found in Indo-Guyanese and
Afro-Guyanese patients.
Secondary ACG cases are present in cases with neovascular
glaucoma, uveitic glaucoma and lens-induced glaucoma.
Management of these cases are
initially attempted medically since
GPHC does not have facility for
YAG Laser Peripheral Iridotomy.
Few of these cases needed
surgical intervention.
Secondary Glaucomas
Secondary Glaucomas do not affect any ethnicity in
particular due to the fact that the primary causes occur
across the board.
Secondary cases include those from
trauma (which has a male predominance),
steroid induced,
inflammatory induced,
lens-induced
and other rare causes.
Congenital Glaucoma
presents rarely and these cases are managed surgically with
long-term follow-up at our clinics.
Medications
Availability of
medications
is a pertinent issue.
Over the past few
months, GPHC
been able to reliably supply four major medications
(generic) to our patients in the public system (Latanoprost,
Brimonidine, Timolol and Pilocarpine).
Due to the heavy demands on the system and large patient
numbers, there are some occasions when the supplies are
depleted. This forces patients to purchase these drops
(which is not affordable for pensioners).
Patient Education
Patient education is a key issue
in glaucoma management.
Careful counselling is important so
that patients are educated on the
pattern of visual loss, their options for
treatment and also the irreversibility
of glaucomatous optic neuropathy.
At
Doctor-patient counselling is difficult
in a public system where clinics are overcrowded and
overtaxed with limited human resources.
Alternatives are to have leaflets that are patient friendly and
dedicated counsellors.
Compliance
It is difficult sometimes for patients to understand visual loss
from glaucoma if they aren’t having a noticeable scotomas
or blurred visual effects. This affects their compliance.
Hence, counselling is important.
Compliance is usually not an issue in patients with advanced
visual field loss, who are willing to give consent for any
surgical procedure.
Treatment Protocols
Most international protocols recommend initialising
treatment of glaucoma patients with medical therapy
(topical eye drops).
The most economical eye drop used in our public system
is Gutt Timolol 0.5% which gives about 10-20% decrease in
initial IOP reduction. It is a drug with good tract record,
well tolerated and there are rare side-effects
(mostly in asthmatic patients).
Patients are then put on 2nd, 3rd and 4th drug therapies until
maximum tolerated medical therapy is achieved
(prostaglandin analogues, alpha-agonists, CA-Inhibitors).
Surgery is recommended for
patients who do not respond to
medical therapy since laser
trabeculoplasty
is not an option in Guyana.
Trabeculectomy with mitomycin-C
is the usual procedure for young
patients and older patients with
clear lens.
In older patients with moderate-severe cataracts are
recommended for combined procedures.
Angle closure patients are monitored after having PIs done.
Rarely, a few severe cases are managed surgically.
Secondary glaucomas (especially inflammatory-induced
cases) are difficult to control with medications
(due to IOP-raising effect of steroids) and hence,
eventually they are recommended for surgical intervention.
Almost all congenital cases are recommended for surgery.
Conclusion
Glaucoma (OAG) is a pertinent issue for Guyana, since it is
the worldwide #1 leading cause of irreversible visual loss.
Thorough evaulation with diagnosis and treatment is essential
with the tools we have available – tonometry (IOP),
funduscopy (optic nerve evaluation), pachymetry (central
corneal thickness) and gonioscopy (evaluation of angle).
Patient education, compliance and availability/cost of
medications are also key issues.
One thing that is certain in patients across all racial and ethnic
divides: “many are not aware that they have glaucoma.”
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