Rule based paradigm was used as the method of knowledge representation. The knowledge base contains the Facts and Rules. The rule contains expression of relationship between the hypothesis and the evidence and in this case the relationship between the disease and the symptoms. The hypothesis and the disease profiles were provided by domain expert in the form of signs, symptoms, risk factors, treatment, images and certainty factors. The purpose of this is to convert these intentions into appropriate facts and rules in the knowledge base (See Figure 3.22)
3.8.4.1.1 The Design of Facts
The facts declared in the knowledge base are declaration of truth about eye diseases, symptoms, signs, risk factors and treatment as provided by the eye doctor (domain expert)
The syntax used for declaration of knowledge base facts is as follows:
factName (factArgumentList).
This is further illustrated as follow:
diseaseSymptoms (glaucoma, headache).
diseaseSymptoms (glaucoma, visualFieldLoss).
disease (glaucoma).
sign (constricted pupil).
symptom (tearing).
symptom (visualFieldLoss).
riskFactor (hypertension) .
treatment (wash eye with warm water).
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Figure3.22: Knowledge Base and working memory structure
3.8.4.1.2 TheDesign of Rules
The rule contains an expressed relationship between different facts and (at times) other rules and joined by logical connectors (AND, OR, NOT). In this study, the rule contains expressed relationships between facts on eye diseases, symptoms, signs, risk factors and treatment with declaration of certainty factor (CF) for each rule.
The general syntax for defining the rule is:
ruleName:- fact1(fact1Arguement), fact1(fact1Arguement),…. factN(factNArguement) <CF>
This can be further illustrated with the following example:
Rule1>
Diagnosis(X):- disease (X), symptom(Y), diseaseSymptoms (X, Y), CfX=0.6, CfY = 0.5
Designing rules as illustrated above, involved using variables as placeholders for diseases and symptoms CfX represents the certainty factor from the working memory submitted by the patient during
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consultation session while CfY represents the certainty factor initially attached to the rule in the knowledge base by the domain expert. X is a variable representing any eye disease and Y is a variable representing any symptom.
The knowledge contained in the above rule example states thus:
The diagnosis of an eye disease, X, with symptom, Y, is inferred if X and Y are known eye disease and symptom respectively,given that the probability/ certainty factor of Symptom, CfY, provided by the patient during consultation is 0.6 and the probability/certainty factor of the Disease, CfX, provided by the domain expert during knowledge acquisition is 0.5.
3.8.4.1.3 The Working Memory
The working memory stores the goal facts which are used to query the facts and rules in the knowledge base during a program run. This type of fact represents the evidence provided by the patient and
therefore is associated with certainty factor value.
The goal or working memory fact was declared with following syntax>
symptom (factName) Cf= X Ex: symptom (headache) Cf = 0.6
3.8.4.1.4 Domain Knowledge and knowledge acquisition of Eye diseases
The information used by eye doctors (domain experts) to make diagnosis often come from the following sources.
a) Direct questioning to get the medical history, b) Physical eye examination to get the signs,
c) Visual acuity measurement to determine the extent of vision loss or damage d) Laboratory/medical imaging tests to determine cause of eye disease.
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From the combination of the examination methods mentioned above (a-d), eye doctors can associate some group of symptoms to a particular or group of eye diseases. Details of information elicited from the above sources is shown below.
a) Direct questioning/ medical history This can reveal the following information
i. Severity of the eye condition ii. Duration of condition
iii. Age of onset
iv. Types of symptoms experienced v. Previous treatment
vi. Any resolution over time vii. recent change in life style viii. Level of education
ix. Current Drugs/medications x. Presence systemic disease
xi. Evidence of previous Hospital admissions
xii. Evidence of previous trauma including the head region xiii. Marital status
xiv. present job
xv. food or drug allergy
xvi. history of recent weight change xvii. history of headaches
xviii. history Loss of consciousness
127 xix. history of seizures.
xx. Family History of eye disease xxi. genetic defect in the family b) Physical examination
This can reveal the following information:
i. Presence of eye disease ii. type of eye disease iii. extent of defect
iv. Presence of eye discharge v. color of eye discharge vi. color of eye
vii. level of visual field viii. color blindness
ix. low contrast sensitivity x. intra-ocular pressure xi. prognosis of the condition c) Visual acuity measurement
This can reveal the following information:
i. current level of visual acuity ii. degree of vision loss
iii. the better seeing eye iv. the preferred eye
v. presence of blindness
128 vi. need for eye glass
vii. need for visual rehabilitation
d) Laboratory/medical imaging tests and their implications.
The following information will be revealed:
i. Culture and sensitivity>> bacterial conjunctivitis
ii. Skull Xray/CT scan >> orbital mass, foreign body, cancer iii. FBS: ocular diabetics
iv. SEUR: Renal Disease v. FBC: Anaemia
vi. Serum electrolytes: Cardiac diseases vii. A & B scan: Glaucoma
viii. MPS: Macula disease
ix. OCT: Cataract, Retinal disease
x. CVF: Glaucoma and visual field defects
xi. Blood smear: Cerebral malaria with ocular involvement
The direct implication of the information derived from these sources is that they are used in generating the Signs, Symptoms, Risk Factors and treatment of eye disease as will be illustrated in chapter 4 (Tables 4.10 – 4.16)
3.8.4.1.5 General Rules of treatment of Eye Diseases
The treatment of eye diseases is dependent on its cause or etiology through disease markers such as signs, symptoms and risk factors extracted directly or indirectly form the patient. For instance the symptoms are gotten directly through medical history and oral interview during consultation session whereas the signs are gotten from both physical examination and indirectly from investigative studies
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such as laboratory and radiological results. This rule is illustrated in Table 3.11. The complete rules are shown in table 4.11
Table 3.11: Rules of eye disease treatment
Disease Symptoms Treatment
Age Related Macular
Degeneration ARMD
Increased sensitivity to light
Color vision defect
Blurring of central vision
Image distortion
Inability to recognize faces from distance
Require brighter light to read
Visual hallucination
Anti VEGF Drug For Wet ARMD
Balanced Diet Rich In Oxidants
Laser Photocoagulation
Low Vision For Dry ARMD
Photodynamic Therapy
Polaroid Or Anti-Reflective Lenses
Quit Smoking
Aides Pupil
Increased sensitivity to light
Light glare
Difficulty reading near prints while below 35 years (early presbyopia)
Unequal pupil size
Bifocal Spectacle
Cosmetic Masking Contact Lens
Photochromic Lenses
Pilocarpine or Brimonidine To Constrict Pupil
Polaroid Or Anti-Reflective Lenses