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SurgeryOphthalmologyChronic Visual Disturbance Loss

Chronic Visual Disturbance and Loss

Introduction

Chronic visual disturbance or loss is a common presentation in Canadian primary care and a high-yield topic for the MCCQE1. Unlike acute visual loss, which is often a vascular or neurological emergency, chronic visual loss typically follows a progressive course over months to years.

For MCCQE1 preparation, candidates must demonstrate the ability to differentiate between refractive, media, retinal, and optic nerve pathologies. Furthermore, applying the CanMEDS roles—particularly Medical Expert (diagnosis) and Health Advocate (impact on driving, falls risk, and independence)—is essential.

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Canadian Context: With Canada’s aging population, the prevalence of age-related eye diseases like macular degeneration and cataracts is rising. Understanding the triage system for ophthalmology referrals and wait-time management is part of the Canadian healthcare reality.

MCCQE1 Objectives and Clinical Approach

The Medical Council of Canada (MCC) expects candidates to assess patients with chronic visual changes efficiently.

Clinical History

A structured history is vital to narrow the differential diagnosis.

Step 1: Characterize the Visual Loss

Determine if the loss is:

  • Monocular vs. Binocular: Monocular suggests anterior visual pathway (eye or optic nerve). Binocular suggests chiasmal or retro-chiasmal pathology.
  • Central vs. Peripheral: Central loss impacts reading/faces (macular). Peripheral loss impacts navigation (glaucoma, retinitis pigmentosa).
  • Distance vs. Near: Myopic shift (nuclear sclerosis) vs. Presbyopia.

Step 2: Identify Associated Symptoms

  • Glare/Halos: Suggests cataracts.
  • Metamorphopsia (Distortion): Straight lines appearing wavy suggests macular pathology (e.g., AMD).
  • Night Blindness: Retinitis pigmentosa or Vitamin A deficiency.
  • Pain: Chronic visual loss is typically painless. If painful, reconsider chronic uveitis or intermittent angle-closure.

Step 3: Review Past Medical History

  • Systemic Disease: Diabetes (retinopathy), Hypertension, Thyroid disease, Giant Cell Arteritis (usually acute, but can have prodromal symptoms).
  • Medications: Corticosteroids (cataracts, glaucoma), Hydroxychloroquine (maculopathy), Ethambutol (optic neuropathy).

Physical Examination

The Pinhole Test

Always perform a pinhole test if visual acuity is reduced (< 20/20 or 6/6). If vision improves with the pinhole, the cause is refractive error or cataract. If it does not improve, suspect retinal or optic nerve pathology.

  • Visual Acuity: Snellen chart (standard in Canada).
  • Confrontation Visual Fields: Detects hemianopsia or quadrantanopsia.
  • Pupillary Exam: Check for Relative Afferent Pupillary Defect (RAPD)—indicates optic nerve disease or extensive retinal damage.
  • Direct Ophthalmoscopy: Assess the Red Reflex (cataracts), Optic Disc (glaucoma/cupping), and Macula (drusen/hemorrhage).

Differential Diagnosis of Chronic Visual Loss

Categorizing by anatomical location is the most effective strategy for the MCCQE1.

1. Refractive Error

  • Most common cause of gradual visual decline.
  • Presbyopia: Loss of accommodation >40 years old.
  • Myopia/Hyperopia: Gradual changes.
  • Diagnosis: Improves with pinhole.

2. Cataracts

  • Opacification of the crystalline lens.
  • Symptoms: Blur, glare (especially night driving), myopic shift (“second sight”).
  • Risk Factors: Age, UV exposure, Diabetes, Steroids, Trauma.
  • Exam: Diminished red reflex, lens opacity on slit lamp/ophthalmoscopy.

High-Yield Conditions for MCCQE1

1. Cataracts

Cataracts are the leading cause of reversible blindness.

  • Pathophysiology: Oxidative damage to lens proteins.
  • Management:
    • Conservative: Glasses update.
    • Surgical: Phacoemulsification with Intraocular Lens (IOL) implantation.
    • Canadian Indication: Surgery is indicated when vision loss interferes with Activities of Daily Living (ADLs) or occupational requirements (e.g., driving).

Differentiating Dry vs. Wet is crucial.

FeatureDry AMD (Non-Exudative)Wet AMD (Exudative)
PathologyAtrophy of RPE, Drusen accumulationChoroidal Neovascularization (CNV)
Prevalence85-90% of cases10-15% of cases
ProgressionSlow, gradual (years)Rapid (weeks to months)
SymptomsCentral scotoma, need more lightMetamorphopsia, central blind spot
TreatmentAREDS2 vitamins, Smoking cessationIntravitreal Anti-VEGF injections
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MCCQE1 Tip: Any patient >50 presenting with metamorphopsia (wavy lines) needs urgent ophthalmology referral to rule out Wet AMD. Use the Amsler Grid for home monitoring.

3. Primary Open-Angle Glaucoma (POAG)

Chronic, progressive optic neuropathy.

  • Screening: Intraocular Pressure (IOP) is a risk factor, not diagnostic. Diagnosis requires disc changes + visual field loss.
  • Treatment Ladder:
    1. Prostaglandin analogues (Latanoprost) - increase uveoscleral outflow.
    2. Beta-blockers (Timolol) - decrease aqueous production.
    3. Laser Trabeculoplasty (SLT).
    4. Trabeculectomy (Surgery).

Canadian Guidelines

Familiarity with guidelines from the Canadian Ophthalmological Society (COS) and Diabetes Canada is expected.

Diabetic Retinopathy Screening (Diabetes Canada)

  • Type 1 Diabetes: Screen 5 years after onset (if ≥ 15 years old).
  • Type 2 Diabetes: Screen at time of diagnosis.
  • Frequency: Annually (or every 1-2 years if no retinopathy and good glycemic control).
  • Pregnancy: Screen in first trimester.

Glaucoma Screening (COS)

  • Routine screening for individuals aged 40–50 every 2–4 years.
  • Individuals aged 65+ every 1–2 years.

Management Principles

When to Refer

Red Flags Requiring Urgent/Semi-Urgent Referral

  • Sudden onset of distortion (Metamorphopsia) → Wet AMD rule-out.
  • IOP > 30 mmHg.
  • Unexplained RAPD.
  • Visual field defects respecting the vertical midline (chiasmal/neurological).

General Measures

  • Refraction: Update prescription.
  • Low Vision Aids: Magnifiers, large print (Health Advocate role).
  • Driving Safety: Physicians in Canada have a duty to report patients unfit to drive due to visual impairment (rules vary by province, generally best corrected acuity < 20/50 or significant field loss).

Key Points to Remember for MCCQE1

  • Painless gradual loss is the hallmark of chronic visual disturbance.
  • Cataracts cause glare and myopic shift; treatment is surgical based on QoL.
  • AMD affects central vision. Wet AMD is treatable with Anti-VEGF; Dry AMD is managed with lifestyle/vitamins.
  • Glaucoma affects peripheral vision first; cup-to-disc ratio is the key physical finding.
  • Pinhole test differentiates refractive error from pathology.
  • Diabetes: Screen T2DM at diagnosis!

Sample Question

Case Presentation

A 76-year-old female presents to your family medicine clinic complaining of difficulty reading and sewing over the past 3 months. She states that when she looks at the bathroom tiles, the straight lines appear “wavy” and distorted. She has a history of hypertension and a 30-pack-year smoking history. Visual acuity is 20/60 in the right eye and 20/25 in the left eye. There is no pain or redness.

Question

Which of the following is the most likely diagnosis?

  • A. Primary Open-Angle Glaucoma
  • B. Dry Age-Related Macular Degeneration
  • C. Wet Age-Related Macular Degeneration
  • D. Nuclear Sclerotic Cataract
  • E. Diabetic Retinopathy

Explanation

The correct answer is:

  • C. Wet Age-Related Macular Degeneration

Explanation: The patient presents with metamorphopsia (straight lines appearing wavy), which is the hallmark symptom of Wet (Exudative) Age-Related Macular Degeneration (AMD). The acuity loss is central (affecting reading/sewing) and relatively rapid (3 months), consistent with the development of choroidal neovascularization. Risk factors include age, female gender, and significant smoking history.

  • A. Primary Open-Angle Glaucoma: Typically presents with asymptomatic, gradual peripheral visual field loss (“tunnel vision”). Central vision is preserved until late stages. Metamorphopsia is not a feature.
  • B. Dry AMD: While this causes central vision loss, it is typically slower and more gradual (years). It presents with scotomas (blind spots) rather than the pronounced distortion (metamorphopsia) seen in Wet AMD, although Dry can convert to Wet.
  • D. Cataract: Presents with general blurriness, glare (especially at night), and a myopic shift. It does not typically cause metamorphopsia.
  • E. Diabetic Retinopathy: The patient has no history of diabetes. While macular edema can cause distortion, the clinical picture strongly points to AMD given the age and specific complaint of wavy lines.

References

  1. Medical Council of Canada. MCCQE Part I Objectives: Visual Disturbance and Loss. Available at: mcc.ca 
  2. Canadian Ophthalmological Society (COS). Clinical Practice Guidelines for the Management of Glaucoma in the Adult Patient.
  3. Diabetes Canada Clinical Practice Guidelines Expert Committee. Retinopathy. Can J Diabetes. 2018;42(Suppl 1):S210-S216.
  4. Toronto Notes 2024. Ophthalmology Chapter. Toronto: Toronto Notes for Medical Students, Inc.
  5. Lippincott, Williams & Wilkins. The Wills Eye Manual: Office and Emergency Room Diagnosis and Treatment of Eye Disease. 7th Edition.
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