Basics of screening and its application in ophthalmology

1. Screening in Ophthalmology
Presenter : Dr. Mahamud Adnan
DO Resident
NIO&H
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2. Chairman : Professor Shawkat Ara Shakoor
Head,Department of Community Ophthalmology and Oculoplasty-Green unit
NIO & H
Moderator : Dr.Shafiul Mostafiz
Assistant Professor
Fellow department of Oculoplasty
NIO & H.
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3. Definition :
 Screening is the presumptive identification of individuals in
a defined population at risk likely to be affected by an
asymptomatic or subclinical condition who can be
benefited by being further investigated.
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4.  The Commission on Chronic Illness, USA in 1951, defined
screening as: "The presumptive identification of disease or
defect by the application of tests, examinations or other
procedures which can be applied rapidly to sort out
apparently well persons who probably have a disease, from
those who probably do not.”
 A screening test is not intended to be diagnostic - persons
with positive or suspicious findings must be referred to their
physicians for diagnosis and treatment."
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5. Uses of Screening :
 Case Detection.
 Control of Disease.
 Research.
 Health Education.
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6. Purpose of Screening :
 Reducing disease burden.
 Classifying people to likelihood of having a particular
disease.
 Identifying high risk groups who needs further evaluation.
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7. Types of Screening :
 The process of screening can be accomplished in different
ways, by using different methods :
1. MASS SCREENING :
This method involves the examination of the whole
population for the detection of the disease.
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8. 2. TARGETED OR HIGH RISK SCREENING :
This method is more effective and includes only individuals
who are at a high risk of suffering from an ailment.
3. OPPORTUNISTIC SCREENING :
Here, only the individuals attending a hospital or a
specified health centre with an unrelated complaint are
examined for the disease of interest.
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9.  Screening may be undertaken for one or more diseases at
the same time by using one or a combination of tests.
This can be classified as:
1. Monophasic Screening:
Where only one disease condition is screened at a
point in time.
2. Multiphasic Screening:
More than one disease condition can be screened at the
same time.
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10. Principles of screening :
 Some essential criteria that should be met before instituting
a screening programme were postulated by Wilson and
Jungner in 1968. They laid out what were later referred to
as the
'Ten Commandments of Screening' :
1. The condition should be an important public health
problem.
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11. 2. The natural history of the condition from the latent to
manifest disease should be adequately under- stood.
3. There should be a recognizable latent or early
asymptomatic stage of the disease, during which
identification will lead to improved prognosis or outcome.
4. There should be an accepted and effective treatment for
the patients with recognized disease.
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12. 5. Facilities for full diagnostic work up and treatment
should be available.
6. There should be a suitable test available which should
be valid.
7. The test should be acceptable both to the public as
well as the professionals.
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13. 8. There should be an agreed policy on whom to treat as
patients, including the management of borderline disease.
9. Case finding should be a continuous process.
10. The cost of early diagnosis and treatment should be
economically balanced in relation to the total expenditure
on medical care
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14.  The principles of screening can be discussed by classifying
them as:
A - Disease criteria
B - Test criteria
C - Diagnostic and treatment infrastructure
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15. Disease criteria :
The different disease criteria are as follows –
 Seriousness of disease
 Natural history of the disease
 Availability of effective treatment
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16. Test criteria :
Any screening test contemplated should satisfy the following
criteria:
1. The test should be cheap.
2. The test should be simple and easy to do.
3.The safety of the test is very important. Invasive procedures
are thus generally unsuitable for screening purposes. The
tests should impose minimal discomfort on the patients
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17. 4. The reliability of the screening test needs to be carefully
considered.
Reliability refers to the consistency of results when
the test is repeated on different occasions.
 Reliability can be affected in different ways:
- Individual biological variation.
- Instrument error.
- Observer recording.
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18. 5. The level of validity of a screening test is also an important
determinant.
A test is said to be valid, when it correctly measures what it
is supposed to measure. A valid test thus correctly
categorizes people into those with and those without the
disease.
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19.  Validity :
is measured by sensitivity and specificity.
In addition to these two computations, it is also important
to consider the positive and negative predictive values.
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20.  Sensitivity :
This refers to the proportion of truly diseased individuals
in the population who have been correctly identified as
diseased by the screening test.
It is also related to as the Detection Rate or the True
Positivity Rate.
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21.  Specificity:
This relates to the proportion of the normal individuals
who are correctly labeled as non-diseased by the screening
test.
It is also called the True Normal Rate or the True
Negative Rate.
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22.  Sensitivity :
a/(a+c)*100
 Specificity :
d/(b+d)*100
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23. Predictive value:
 Positive Predictive Value:
This indicates the probability of an individual
suffering from the disease, when the screening test
indicates a positive result.
- Percentage of test positives who are truly disease
positive.
- If positive predictive value increase false positive
decrease.
Calculation = a/(a+b)*100 or TP/(TP+FP)*100
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24. cont.
 Negative Predictive Value:
Percentage of test negatives who are truly disease
negative.
- If negative predictive value increase false negative
decrease.
- Calculation = a/(a+b)*100 or TN/(TN+FN)*100
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25. Diagnostic and treatment infrastructure:
 Screening test is basically a preliminary test that identifies
the 'suspects', adequate back up infra-structural facilities
should be available to establish a definitive diagnosis.
 Treatment modalities and protocols on who should be
treated and how, should be clearly defined.It is the bounden
duty of the screening programme to offer the appropriate
intervention to the individual.
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26. Planning :
 Justifying the screening programme
 Identifying people to be screened
 Setting up the screening service
 Ensuring quality
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27. The planning model :
Diagrammatic model of planning
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28. The planning model :
 Deciding where you are – a situational analysis :
1. Assessing needs
2. Assessing resources
 Deciding where you want to be
1. Defining the aim
2. Specifying the objectives
3. Defining priorities and strategies
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29.  Deciding how to get there
1.Preparing a timetable
2.Preparing a budget
 Getting there
1.Establishing a management structure
2.Monitoring progress
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30. Evaluation of screening programmes :
 A screening programme can be evaluated in two main ways :
a. The process of screening
b. The outcome of screening
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31. a. The process of screening :
 Process measure include :
1. The validity of the screening test –
Sensitivity
Specificity
Predictive value
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32. 2. The reliability of screening test.
3. The yield of screening(the number of person screened to
detect one case).
4.The cost per case detected and successfully treated.
5.The coverage of screening.
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33. Screening Process :
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34. b. The outcome of screening :
 Relate to the effectiveness of the screening programme in
reducing -
- mortality,
- morbidity and
- disability.
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35. Examples of Screening Programmes in
Ophthalmology :
 Preschool Vision Screening for Amblyopia and Strabismus
 'Screening' for refractive errors in school children.
 Cataract screening.
 Glaucoma Screening.
 Diabetic Retinopathy Screening.
 Retinopathy of prematurity screening.
 Retinoblastoma screening.
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36. 'Screening' for refractive errors in school children:
 Whom we do screening ?
- Pre-school and school going children.
 Vision problems can affect the physical, intellectual, social
& emotional development of students.
 Child may become blind if the problem remains undetected.
 Poor vision in childhood affects school performance.
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37. Tools :
 Snellen Chart / E- Chart
( 3 meter)
 Trial box with trial frame
 Measuring tape
 Torch light
 Occluder
 Streak Retinoscope
 Ophthalmoscope
 Autorefractometer
 Ishihara Chart
 Registration Book
 Referral Slip
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38. 38

39. Who will do refraction ?
Three Options:
 Ophthalmologist
 Resident / Trainee doctors of Ophthalmology
 Mid level ophthalmic personnel
I. Optometrists
II. Ophthalmic Nurse
III. Ophthalmic technician
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40. FOLLOW UP :
 Once a child has been diagnosed, he/she should be re-
examined at intervals of 1–2 years by the Ophthalmologist.
 This is particularly important for myopic children, as their
myopia might progress.
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41. Cataract screening :
 Target group :
1. Any age
2. Any sex
3. Lower socioeconomic group
4. Remote residents
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42. Tools :
 Stationeries : Pen, color coded papers, etc.
 Torchlight
 BP measuring machine
 Blood sugar measuring machine
 Slit lamp (hand held)
 OT equipments
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43. How we do :
Steps
1. Selection of Screening Sites & Base
2. Adequate announcement/advertisement with sufficient
involvement of locals
3. Appropriate arrangement for medical personnel & others :
Transport, Food, Residency
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44. Screening
1. Registration
2. Screening by Doctors
3. BP & RBS by Medical Assistants
4. Selection by Doctors
5. Transportation to Base/Hospital
6. Surgical Intervention
7. Follow Up @ 1st POD
8. DēA, Return Transportation.
9. 2nd follow up after 7 days.
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45. Glaucoma Screening :
 Whom we do screening ?
- Anyone after 40 years of age.
- Family history is positive.
- Prolong use of corticosteroid.
- History of ocular trauma.
- Medical conditions – DM,HTN
- Other eye-related risk factors – thin cornea.
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46. Screening test :
 The view of American Academy of ophthalmology is that
three test should be performed routinely –
1. Intraocular pressure ( IOP )
2. Optic disc and Nerve fiber layer evaluation
3. Visual field test
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47. Follow up :
 Intra ocular pressure – should be checked at least every 6
months,
 Visual field test - at least once every 12 months,
 Optic nerve (ONFL ,possibly via OCT ) at least once every 12
months.
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48. Diabetic Retinopathy Screening :
 Screening of Diabetic Retinopathy is an important aspect of
DM management worldwide.
Target group :
1. History of diabetes mellitus
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49. Screening test :
 Consist of a complete examination of the fundus through
dilated pupils.
 By a fully trained Ophthalmologist or trained stuff where
ophthalmologist are too few or absent.
According to Early Treatment Diabetic Retinopathy Study (ETDRS)
classification :
The gold standard for the detection of diabetic retinopathy
consists of 30° stereoscopic photography of seven standard
fields on color film. 49

50. Methods of screening for diabetic retinopathy include:
 Visual acuity test
 Blood sugar level test
 Direct and indirect ophthalmoscopy
 Stereoscopic color film fundus photography
 Mydriatic or nonmydriatic digital color and monochromatic
photography.
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51. Follow up schedule :
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53. Retinopathy of prematurity screening :
 Whom we do screening ?
- Low birth weight < 2.5 kg
- Premature delivery before 32 weeks
of pregnancy.
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54. When to screen :
Gestational age(Babies
born)
First ROP screening
Up to 27 weeks 3-4 weeks of postnatal age
From 27 weeks to 32 weeks 4-5 weeks of postnatal age
>32 weeks but birth weight
<1501 gm
4-5 weeks of postnatal age
<32 weeks and birth
weight<1501 gm
4 weeks of postnatal age
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55. Retinoblastoma screening :
 Whom we do screening ?
- White pupillary light reflex.
- Positive family history.
- Siblings of affected one.
- All infants or children with an abnormal red reflex.
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56. Schedule for follow-up visits :
 Follow-up visits for retinoblastoma are usually scheduled:
1. Every 4 weeks during treatment
2. Every 2 to 3 months during the first year after treatment
3. Every 3 to 6 months until age 6 or 7 year
4. Every year after that.
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57. Take home message :
 Screening is an important weapon in the armoury of
prevention , whether it be primary , secondary or tertiary.
 Effective screening may help to reduce avoidable blindness
 Good ground work and planning may lead to a successful
screening programme.
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58. Thank you
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