Strabismus And Amblyopia

Introduction

Welcome to this comprehensive MCCQE1 preparation guide on strabismus and amblyopia. This resource is tailored for Canadian medical students preparing for the Medical Council of Canada Qualifying Examination Part I (MCCQE1). We'll explore these common pediatric ophthalmological conditions, emphasizing Canadian guidelines and practices.

Strabismus

Definition and Epidemiology

Strabismus, also known as "crossed eyes" or "wandering eyes," is a misalignment of the eyes where both eyes do not look at the same point simultaneously.

• Prevalence in Canada: Approximately 2-4% of children under 6 years old
• Risk factors: Prematurity, family history, certain neurological conditions

Types of Strabismus

Clinical Presentation

1. Misalignment of eyes
2. Head tilting or turning
3. Squinting or closing one eye in bright light
4. Poor depth perception

Diagnostic Approaches

Management

Treatment options for strabismus in Canada typically follow this hierarchy:

1. Correction of refractive errors: Prescription glasses
2. Patching therapy: For associated amblyopia
3. Orthoptic exercises: To strengthen eye muscles
4. Botulinum toxin injections: For some types of strabismus
5. Surgical correction: When conservative measures fail

Amblyopia

Definition and Epidemiology

Amblyopia, or "lazy eye," is reduced vision in one or both eyes due to abnormal visual development in childhood.

• Prevalence in Canada: Affects 1-3% of children
• Critical period: Most responsive to treatment before age 7

Types of Amblyopia

1. Strabismic: Due to eye misalignment
2. Refractive: Caused by significant refractive errors
3. Deprivation: Result of obstruction to visual axis (e.g., congenital cataract)

Clinical Presentation

• Reduced visual acuity in affected eye(s)
• No apparent structural abnormalities
• Often asymptomatic in young children

Diagnostic Approaches

Management

Canadian guidelines emphasize early detection and treatment:

1. Optical correction: Prescription glasses for refractive errors
2. Patching therapy: Occlude the better-seeing eye
3. Atropine penalization: Alternative to patching for some cases
4. Vision therapy: Exercises to improve visual function
5. Regular follow-up: Monitor progress and adjust treatment

Canadian Guidelines for Screening and Management

The Canadian Paediatric Society and the Canadian Ophthalmological Society recommend:

1. Vision screening for all children at 6-12 months, 3 years, and 4-5 years of age
2. Referral to an ophthalmologist if strabismus or amblyopia is suspected
3. Early intervention for optimal outcomes
4. Collaboration between primary care providers, optometrists, and ophthalmologists

Key Points to Remember for MCCQE1

• Strabismus and amblyopia are common pediatric ophthalmological conditions in Canada
• Early detection and treatment are crucial for preventing long-term visual impairment
• Strabismus can lead to amblyopia if left untreated
• Patching therapy is a primary treatment for amblyopia in Canada
• Canadian healthcare system covers medically necessary treatments for both conditions
• Familiarize yourself with the Canadian screening recommendations and referral criteria

Sample Question

A 4-year-old girl is brought to her family physician for a routine check-up. Her mother mentions that she has noticed the child's right eye turning inward occasionally over the past few months. On examination, the physician observes an intermittent inward deviation of the right eye. Visual acuity testing shows 20/40 vision in the right eye and 20/20 in the left eye. Which of the following is the most appropriate next step in management?

• A. Reassure the mother and schedule a follow-up in 6 months
• B. Prescribe glasses with a patch over the left eye
• C. Refer to an ophthalmologist for further evaluation
• D. Start eye muscle exercises at home
• E. Recommend alternating eye patching daily

Explanation

The correct answer is:

• C. Refer to an ophthalmologist for further evaluation

This case presents a 4-year-old child with signs of intermittent esotropia (inward turning of the right eye) and possible amblyopia (reduced vision in the right eye). In the Canadian healthcare context, the most appropriate next step is to refer the child to an ophthalmologist for a comprehensive evaluation.

Rationale for the correct answer:

1. The child's age falls within the critical period for visual development.
2. There are signs of both strabismus and potential amblyopia, which require specialist assessment.
3. Canadian guidelines emphasize early referral and intervention for suspected strabismus or amblyopia.

Explanation for the incorrect options: A. Reassurance and delayed follow-up could lead to progression of the condition and missed treatment opportunity. B. Prescribing glasses and patching without a specialist evaluation is premature and may not address the underlying issue correctly. D. Eye muscle exercises are not typically recommended as a first-line treatment without specialist evaluation. E. Alternating eye patching is not appropriate without a proper diagnosis and treatment plan from an ophthalmologist.

References

1. Canadian Paediatric Society. (2016). Vision screening in infants, children and youth. Paediatrics & Child Health, 21(4), 235-240.

2. Canadian Ophthalmological Society. (2019). COS evidence-based clinical practice guidelines for the periodic eye examination in children aged 0-5 years in Canada. Canadian Journal of Ophthalmology, 54(6), 751-759.

3. Bradfield, Y. S. (2013). Identification and treatment of amblyopia. American Family Physician, 87(5), 348-352.

4. Wong, A. M. (2012). New concepts concerning the neural mechanisms of amblyopia and their clinical implications. Canadian Journal of Ophthalmology, 47(5), 399-409.

5. Pediatric Eye Disease Investigator Group. (2002). The clinical profile of moderate amblyopia in children younger than 7 years. Archives of Ophthalmology, 120(3), 281-287.