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The St Kitts Eye StudyGrand Rounds, January 2009

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Content

Background of Project

Screening

Protocol of the St Kitts Eye Study

What we have learned so far

Where do we go from here

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Federation of St Kitts and Nevis

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St Kitts

5 km

168 sq.km

35,000 inhabitants (2001 census)

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St Kitts and Halifax: Connections

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St Kitts and Halifax: Connections

1991: Eye Centre of Joseph N FranceHospital established, with help from Halifax

2001: first proposal for screening project

2003: funds from industryAlcon, Allergan, Merck, Pfizer

2005: it nearly happened2007: it nearly happened (again)

2008: it really happened.

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Glaucoma and black ancestry

St Lucia Study Ophthalmology (1989)

Baltimore Eye Survey Am J Epidem (1991)

The Barbados Eye Study Arch Ophth 1994)

Survey of Ophthalmology (2003)

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Glaucoma and black ancestry

prevalence 3 - 6 higher than in Caucasians

earlier onset & more rapid progression

5 larger prevalence of ocular hypertension (OHT)

risk of progression from OHT to glaucoma

rates of glaucoma-related blindness

Survey of Ophthalmology (2003)

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Glaucoma in the Caribbean

St Lucia Study Ophthalmology, 1989 Sep;96(9):1363-8

1679 individuals, aged 30+ years

VA, IOP, C/D ratio1/3 had supra-threshold screening fields on HFA

positives underwent definitive exam, including threshold fields

Prevalence of 8.8% in the 30+

y population.

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What is Screening?

Identify people whoprobablyhave a disease

from those thatprobably do not.

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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The condition sought should be an important health problem.

There should be an accepted treatment.

The natural history of the disease should be well understood.

There should be a latent or early symptomatic stage.There should be a suitable and acceptable screening test.

Facilities for diagnosis and treatment should be available.

There should be an agreed policy on whom to treat as patients.

Early treatment should be of benefit.

The cost should be economically balanced.

Case finding should be a continuing process.

WHO criteria, after Wilson and Jungner (1968)

Glaucoma screening: worthwhile?

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Glaucoma screening: worthwhile?

S Hatt, R Wormald, J Burr

Cochrane Database of Systematic Reviews 2008Screening for prevention of optic nerve damage

due to chronic open angle glaucoma

Main results

As no trials were identified, no formal analysis

was performed.

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Glaucoma screening: worthwhile?

S Hatt, R Wormald, J Burr

Cochrane Database of Systematic Reviews 2008Screening for prevention of optic nerve damagedue to chronic open angle glaucoma

Main results

As no trials were identified, no formal analysiswas performed.

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The Bottom Line

Screeningcan be cost-effective in high-risk populations.

Most economic evaluations compare tocurrent model of routine case-finding byoptometrists, which does not exist inCaribbean.

Screening tests need very highspecificity to be workable.

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A good screening program

simple, cheap, and accessible

in peripheral health centres

rely on local expertise (nurses, assistants)

good sensitivity, and very high specificity

false-positive rate

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Likelihood ratios

sensitivity / (1 specificity)

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Likelihood ratios

sensitivity / (1 specificity)

Fagan Nomogram

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Likelihood ratios

sensitivity / (1 specificity)

Fagan Nomogram

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Likelihood ratios

sensitivity / (1 specificity)

Example:Moorfields Regression Analysis of HRT

Sensitivity = 65%, Specificity = 95%

Likelihood ratio = 0.65 / 0.05

= 13

Fagan Nomogram

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Brain Teaser

Sensitivity = 50%

Specificity = 95%

Prevalence = 0.3%

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Brain Teaser

Sensitivity = 50%

Specificity = 95%

Prevalence = 0.3%

What is the probability that a patient with

a positive test has the disease?

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Fagan Nomogram

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Fagan Nomogram

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Doctors with an average of 14 yrs experienceDoctors with an average of 14 yrs experience

Answers ranged from 1% to 99%Answers ranged from 1% to 99%

half of them estimating the probability as 50%half of them estimating the probability as 50%

Gigerenzer,Gigerenzer,

BMJ 2003;327:741-744BMJ 2003;327:741-744

5%

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help establish a robust

and effectivescreening

program for St Kitts and

wider Caribbean region

Aim - St Kitts Eye Study

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Questions - St Kitts Eye Study

Which tests provide high specificity and good

sensitivity, in a Caribbean population?

Which combination of tests provides the best

trade-off between performance and effort?

Can new technologies (eg HRT imaging)

improve on the current standard of care?

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Objectives St Kitts Eye Study

Examine a representative sample of 200

individuals >50 yrs with screening tests as

well as gold standard protocol.

Establish combination of screening tests

that provides specificity >98%.

Establish criteria for referral to Eye Centre.

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random sample of St Kitts residents (n=370)

drawn from Social Security list.

invited to participate by letter from Ministry

of Health

completeprotocol of tests, including

screening- and gold standard tests

Design St Kitts Eye Study

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Visual Fields

Frequency Doubling (Matrix) Perimetry

Moorfields Motion Displacement Perimetry

Suprathreshold (white-on-white) Perimetry(all screening tests on one eye only)

Humphrey 24-2 Sita-Standard (both eyes)

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Tonometry

EasyEye NCT (Keeler)

Tonopen (Reichert)

Goldmann Applanation Tonometry (GAT)

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Imaging

Heidelberg Retina Tomograph (HRT2)

Nidek AFC 230 Stereo Fundus Camera

Dilated Fundus Examination (Volk 90D)

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Humphrey Matrix

1% supra-threshold test

Moorfields

Motion Displacement

Perimetry

HFA 76 point 3-zone

supra-threshold test

HFA 24-2 SITA Std

Threshold Visual Fields

Keeler EasyEye

Non-Contact Tonometry

Tonopen

Goldmann Applanation

Tonometry

Heidelberg Retina

Tomograph 2

Fundus Photography

Gonioscopy

Dilated exam of Anterior &

Posterior Segments

Clinical Decision &

Referral (if appropriate)

Consent, Interview,

Visual Acuity SKES: Protocol

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Initial Findings

Invited:

373 individuals (169 women, 204 men)

age range 50 87 yrs

Participated:

172 individuals (46%) of those invited44 individuals (opportunistic)

208 (96%) completed entire program

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Initial Findings

Prevalence of glaucoma

18/172 = 10.5%

8 previously unknown (44%)

Prevalence of Ocular Hypertension

15/172 = 9%12 previously unknown (80%)

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Initial Findings*

Other conditions

Pterygium: almost universal

Significant cataract: ~25%

Diabetic Retinopathy: ??

AMD: very few

* No formal analysis conducted as yet

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Initial Findings*

Visual Fields

High rate of unreliable results with thresholdperimetry.

Moorfields Motion Displacement test easyto explain and well accepted.

Matrix Frequency Doubling: high rate of

abnormal test results

* No formal analysis conducted as yet

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Initial Findings*

Imaging

Optic disc size distribution different from

caucasians (larger number of large discs?)

Fundus photography: significant number of

nerve fibre layer defects as isolated finding.

* No formal analysis conducted as yet

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Initial Findings*

Tonometry

Non-contact tonometry surprisingly well

tolerated (but needs practice).

Impression: NCT appears more accurate &

precise compared to Tonopen.

* No formal analysis conducted as yet

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Where do we go from here?

Formal analysis of test performance,

compared to gold standard of clinical

examination.

Report to Ministry of Health, St Kitts and

Nevis, with suggested paradigm and cost

estimates.

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Younes Agoumi, Carol Beattie, Beulah &Terrela Byron, Balwantray Chauhan,Anthony Crouse, Stacey Durling, Marcelo