Biostatistics/Ophthalmology Basics Flashcards
What are the features of a complete CNIII palsy?
Only lateral rectus and superior oblique will be active
LR = abduction
SO = Downwards and abduction
Result = Down and outward eye turn with mydriasis (dilated pupil) + ptosis (loss of levator palpebrae muscle)
Kevan Otology Page 25
Differential diagnosis of sudden vision loss7
- Vitreous hemorrhage
- Central retinal (Artery or vein) occlusion (pale fundus + cherry red spots)
- Retinal detachment
- Temporal arteritis
- Optic neuritis (if young, consider MS)
- TIA
- Malingering
“Really CANT Open Vision”
R - Retinal detachment
C - Central retinal artery or vein occlusion (pale fundus and cherry spots)
A - Arteritis (temporal arteritis)
N - Not real (malingering)
T - TIA
O - Optic neuritis (if young, consider MS)
V - Vitreous hemorrhage
Normal visual fields
- 90 degrees ipsilateral
- 50 degrees contralateral
https://www.vision-and-eye-health.com/images/xVisualFieldHoriz.gif.pagespeed.ic.iHnN9uU-0e.png
What is strabismus vs. amblyopia?
Strabismus = misalignment of the eyes
Ambloypia = Unilateral or bilateral reduced vision without physiologic defect of one eye or the other (abnormal central processing)
- Does not improve with glasses
- Greater refractive error so the brain suppresses the weaker image
- Treatment = patching the stronger eye (younger = improved outcome)
Differentiate Hordeolum, Chalazion, and Blepharitis
Hordeolum = Infection of lid glands, Rx topical antibiotics
Chalazion = Obstructed meibomian gland, Rx warm compress, tobradex or curettage
“Lazy cuz you don’t wash your face so it gets obstructed”
Blepharitis = Chronic staph infection of the upper lid, associated with seborrhea
“Bugs = staph”
What are the different types of conjunctivitis?
- Virus: Adenovirus (pink eye)
- Bacterial: Staph, Haemophilus influenzae, diplococcus, N Gonorrhea (if ++ purulent)
- Allergic
What are the main causes of:
1. Keratitis
2. Scleritis
3. Iritis
Keratitis:
- HSV
- VZV
Scleritis:
- 50% systemic disease (e.g. RA)
Iritis: (think rheumatoid-y things)
- TB
- Sarcoid
- Ankylosing Spondylitis
- RA
- Reiters (reactive arthritis)
- Behcet’s
- Gonorrhea
What does p < 0.001 mean?
Assuming that H0 is true (ie. there is no difference between the two groups studied), the probability of observing the result obtained in the experiment is 1/1000 (0.1%)
- Therefore the lower the number, the more likely there is a difference between groups because of how unlikely it would’ve been to get your result if the H0 was true (no difference).
- Probability that “H0 is true (no difference between two groups studied)” is 1/1000
H0 = usually defined as “no difference” between groups, therefore p = probability of H0 being true
P = probability that result occurred by chance alone (probability that H0 is true)
What is the precise meaning of a p value < 0.05?
Assuming that the null hypothesis is correct, the probability of obtaining the observed result in a study is < 5% (5/100)
Define the meaning of a 95% confidence interval
If a study is repeated infintely on new samples of individuals, the confidence interval will include the true result 95% of the time
Note: It does NOT mean that there is a 95% chance that the true value falls within the reported confidence intervals
Define Sensitivity
True positive Rate - The proportion of those who have the condition that received a positive results on the test (TP / (TP + FN))
100% sensitive = negative test rules the condition out (SNout)
- If test positive, can be true positive or false positive, therefore sensitivity doesn’t tell you about positive tests as well. Just tells you that if you DO TRULY have the disease, then you will be positive
- If you test negative, can’t be a false negative because 100% Sensitivity means FN = 0.
Vancouver Page 69
Define Specificity
True negative Rate - The Proportion of thsoe who do not have the condition that received a negative result on this test
- TN / (FP + TN)
100% specific = Positive test rules the condition in (SPin)
- If test negative, can be true negative or false negative, therefore specifisity doesn’t tell you about negative tests as well. Just tells you that if you DON’T TRULY have the disease, then you will be negative
- If you test positive, can’t be a false positive because 100% Specificity means FN = 0.
Vancouver Page 69
Define Type 1 vs. Type 2 error
Type 1 Error (alpha): Chance of finding a difference when there isn’t one
- Reject the H0 (null hypothesis) when it is in fact true (false rejection)
- False positive rate
- 1 - specificity (specificity has FP in the equation)
Type 2 error (beta): Chance of finding no difference when there is one
- False acceptance of H0 (null hypothesis)
- Dependent on Type 1 error and the sample size
- False negative rate
- 1 - sensitivity
- Generally worse than a Type 1 error (don’t want inaccurate false negatives, if a patient is actually positive!)
Null hypothesis = there is no difference. If you reject this that means there is a difference, ie. you would get a positive result. If you accept this (not reject) that means there is no difference, ie. you would get a negative result.
Think of rejection as a positive result.
Not rejection is a negative result.
If you reject when its actually true, then its a false rejection (ie. false positive)
Vancouver Page 69
https://www.scribbr.com/wp-content/uploads/2021/01/type-i-and-ii-error-2.png
Define prevalence calculation
Condition positive / Total # of people in the sample
Define power
Power = Sensitivity = 1 - beta (type 2 error)
Probability of rejecting a false null hypothesis
