Causes of Blurred Vision
Blurred vision has multiple etiologies that can be systematically categorized into ocular and systemic causes, with refractive errors being the most common cause overall, followed by cataracts, age-related macular degeneration (AMD), and diabetic retinopathy in adults. 1
Primary Ocular Causes
Refractive Errors
- Most common cause of impaired visual acuity in the US and worldwide 1
- Includes myopia (nearsightedness), hyperopia (farsightedness), and presbyopia
- Presbyopia affects most individuals around age 45 years as the lens loses flexibility 1
- Prevalence of hyperopia increases with age while myopia tends to decrease 1
- Family history strongly correlates with both myopia and hyperopia 1
Cataracts
- Account for approximately 50% of bilateral low vision cases in adults over 40 1, 2
- Clouding of the lens causing impaired visual acuity, increased glare sensitivity, and reduced contrast sensitivity 1
- Prevalence increases sharply with age: 50% of US adults ≥75 years have cataracts 1
- Risk factors: older age, smoking, alcohol use, UV light exposure, diabetes, corticosteroid use 1
Age-Related Macular Degeneration (AMD)
- Progressive retinal deterioration causing blurred vision and central vision loss 1
- Leading cause of blindness in adults >65 years 1
- Prevalence: 6.5% in adults ≥40 years, increasing to 13.4% in those ≥60 years 1
- Two forms:
- Risk factors: older age, smoking, obesity, low dietary green leafy vegetables, elevated cholesterol, cardiovascular disease, family history 1
Diabetic Retinopathy
- Prevalence: 28.5%-40.3% in individuals ≥40 years with type 1 or type 2 diabetes 2
- Risk factors: increasing diabetes duration, elevated HbA1c, high systolic blood pressure, elevated serum lipids 2
- Findings: microaneurysms, hemorrhages, lipid exudates, macular edema, neovascularization 2
Glaucoma
- Open-angle glaucoma: Prevalence 3.4% in African Americans, 1.7% in White Americans ≥40 years 2
- Angle-closure glaucoma: Higher rates in Inuit and Asian populations 2
- Risk factors: African/Hispanic/Latino descent, increased age, family history, elevated intraocular pressure 2
Dry Eye Disease
- Tear film instability causes fluctuating vision with blinking, blurred vision, glare, and eye fatigue 3
- Mechanisms include decreased stability of postblink higher-order aberrations and increased light scattering 3
- Ocular surface damage in the central cornea increases higher-order aberrations leading to persistent blurred vision 3
Other Ocular Conditions
- Corneal disorders: Corneal ectasia, corneal dystrophies 2
- Choroidal nevi: 5-8% prevalence, increases with age, more common in White Americans 2
- Acute retinal necrosis: Rare, typically in immunocompromised patients, caused by varicella zoster virus, herpes simplex virus, or rarely CMV 4
Systemic Causes with Ocular Manifestations
Neurological Disorders
- Pupillary dysfunction: Horner's syndrome, midbrain tumor, aneurysm 2
- Ocular motility issues: Myasthenia gravis, CNS defects, aneurysm, multiple sclerosis 2
- Visual field defects: Cerebrovascular accidents, chiasmal tumors 2
- Increased intracranial pressure 2
Endocrine Disorders
- Graves' disease: External examination findings, ocular motility abnormalities 2
- Cushing's syndrome: Can present with episodic blurry vision, though unusual 5
- Diabetes mellitus: Posterior segment findings 2
Vascular Disorders
- Systemic hypertension: Posterior segment changes 2
- Vasculitis: Immune-mediated diseases 2
- Cerebrovascular disease 2
Infectious Diseases
- AIDS, tuberculosis, syphilis, histoplasmosis, toxoplasmosis 2
- Can affect anterior or posterior segments 2
Autoimmune/Inflammatory Conditions
Metabolic/Genetic Disorders
- Lens involvement: Alport syndrome, Apert syndrome, myotonic dystrophy, Wilson disease, homocystinuria, Marfan syndrome, Weill-Marchesani syndrome 2
- Metabolic storage diseases: External examination and posterior segment findings 2
- Vitamin A deficiency: Anterior segment changes 2
Drug/Toxicity-Related
- SSRIs: Significant association with vision blurred, visual impairment, mydriasis; most events occur within first 30 days of treatment 6
- Hydroxychloroquine, tamoxifen, phenothiazines: Posterior segment toxicity 2
- Heavy metal toxicity: Anterior segment findings 2
- Corticosteroids: Cataract development 1
Neoplastic
- Orbital tumors, primary or metastatic tumors affecting posterior segment 2
Clinical Pitfalls
Age is the most important risk factor across multiple causes of blurred vision, making comprehensive evaluation essential in older adults 1. The prevalence of impaired visual acuity is higher among persons of lower socioeconomic or educational status and those without private health insurance 1.
Early symptoms of serious conditions like neovascular AMD may be subtle, making comprehensive eye examination critical for early diagnosis and treatment at a more favorable stage 2. Anti-VEGF treatment given within 2 years of neovascular AMD diagnosis reduces legal blindness and visual impairment 2.
When evaluating blurred vision, distinguish between acute versus chronic onset, monocular versus binocular involvement, and associated symptoms (floaters, photopsia, metamorphopsia, scotomas) to narrow the differential diagnosis 7.