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Questions and Answers
What happens to astigmatism when scoping off-axis?
How do you scope a constant ET on axis?
What is the recommended working distance for the Near Retinoscopy Method (Mohindra)?
What is the dosage of Cyclopentolate for a 3-year-old?
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What is one way to determine if you have adequate cycloplegia?
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What happens to the spherical component when scoping off-axis?
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What is the purpose of subtracting 1.25 D from the sphere value in the Near Retinoscopy Method (Mohindra)?
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What is the recommended dosage of Cyclopentolate for an 8-month-old?
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What is the primary purpose of keratometry?
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In non-cycloplegic static retinoscopy, what is done for out-of-phoropter refraction for children and deviations > 15∆?
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What is the working distance in the Near Retinoscopy Method (Mohindra)?
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What is the duration of action of Tropicamide?
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What is the dosage of Cyclopentolate for children under 1 year?
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What is the toxicity symptom of Atropine?
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How is the adequacy of Cycloplegia determined?
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What amount of hyperopia is associated with the future development of esotropia (ET) and amblyopia?
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What factor needs to be controlled when performing retinoscopy on a patient with strabismus?
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What is the characteristic of Tropicamide?
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What percentage of children with strabismus have abnormal refractions?
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What is the refractive power difference between the two eyes that commonly causes amblyopia?
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What is the effect of increased accommodation on refractive error?
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What is the percentage of amblyopia cases caused by anisometropia?
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What is the refractive error that increases the risk of strabismus by 20 times in children at 1 year?
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What is the effect of retinal eccentricity on astigmatism?
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What is the degree of visual axis deviation to avoid significant errors in astigmatic and spherical components?
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What percentage of comitant esotropias resolve with corrective lenses?
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Study Notes
Refractive Status in Strabismus and Amblyopia
Importance of Refractive Status
- Refractive status is a crucial factor in the etiology of strabismus and amblyopia
- Strabismus is often caused by refractive issues
- Amblyopia is commonly caused by anisometropia (unequal refractive power between the two eyes)
Key Findings
- One-third of comitant esotropias (ETs) resolve with corrective lenses
- Approximately 50% of amblyopia cases are caused by anisometropia
- 72% of children with strabismus have abnormal refractions
- Refractive errors leading to strabismus and amblyopia:
- Hyperopia > +2.00 D
- Anisometropia > +1.00 D in any meridian
- Children with hyperopia > +2.50 D at 1 year are 20 times more likely to develop strabismus
- Hyperopia > +3.50 D at 6-8 months increases the risk of strabismus by 13 times and amblyopia by 6 times by age 4
Scoping Off Axis
- Astigmatism increases progressively with retinal eccentricity and is nearly independent of central refraction
- Spherical component decreases as a function of retinal eccentricity
- Stay within 10 degrees (~17∆) of the visual axis to avoid significant errors in astigmatic and spherical components
Controlling Accommodation
- Increased accommodation results in an artificial increase in negative or decrease in positive refractive error
- Indicators of accommodation:
- Abnormally small pupils or decreasing pupil size beyond normal miosis during retinoscopy
- Use projected targets or cartoons to control accommodation effectively
Keratometry
- Purpose: Confirm astigmatic power and axis found by retinoscopy
Noncycloplegic Static Retinoscopy
- Procedure:
- Initial screening
- Scoping strabismic patients:
- For ETs and vertical deviations: Hold correcting prism in front of the fixating eye
- For XTs: Align Purkinje's images or use a corrective prism base in (BI)
- Considerations:
- Out-of-phoropter refraction for children and deviations > 15∆
- Astigmatism increases and spherical power decreases as you go off-axis
Near Retinoscopy Method (Mohindra)
- Procedure:
- Patient sits in a chair or on a parent's lap
- 50 cm working distance with room lights out
- Patient fixates on the retinoscope; monitor corneal reflex to ensure scoping on axis
- One eye occluded
- Neutralize primary meridians and subtract 1.25 D from the sphere value (for children > 2 years, subtract 1.00 D)
- Comparison: Correlates with cycloplegic methods about 35% of the time
- Improvements: Use 1.00 D for children and 0.75 D for infants instead of 1.25 D; NRM may slightly underestimate hyperopia
Cycloplegic Retinoscopy
- Tropicamide:
- Characteristics: Short duration of action, brief peak time, poor at eliminating high accommodative tonus of childhood
- Not recommended for cycloplegia
- Response: Mydriasis in 20-40 min, Cycloplegia in 60-180 min
- Cyclopentolate (Cyclogyl):
- Dosage:
- < 1 year: 0.5% solution, 2 drops (1 drop, wait 5 min, add 1 drop)
- 1 year: 1.0% solution, 2 drops (1 drop, wait 5 min, add 1 drop)
- Response: Mydriasis within 30-60 min, Cycloplegia max in 30-45 min
- Duration: Mydriasis for ~24 hours, Cycloplegia for 8-24 hours
- Toxicity symptoms: Restlessness, hallucinations, memory loss, etc
- Dosage:
- Atropine:
- Dosage:
- < 1 year: 0.5% ointment/solution BID x 3 days before exam
- 1 year: 1.0% ointment/solution BID x 3 days before exam
- Response: Mydriasis in 30-45 min, Cycloplegia max in 3-6 hours
- Duration: Mydriasis for up to 12 days, Cycloplegia for 10-18 days
- Toxicity symptoms: Dry skin, fever, tachycardia, delirium
- Dosage:
Determining Adequacy of Cycloplegia
- Pupil size is not an indicator
- Look for < 2D accommodative amplitude or a +2.00D lag in dynamic retinoscopy
- Use a single line of threshold Snellen at distance; if adding -0.75 D reduces visual acuity (VA), adequate cycloplegia is achieved
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Description
Learn about the importance of refractive status in strabismus and amblyopia, including their causes and effects. Discover how corrective lenses can resolve comitant esotropias and more.
