Blurred vision

Blurred vision is an ocular symptom.

The small print in an ingredients list is clear to healthy young eyes

Older eyes may have difficulty reading small print

Causes

There are many causes of blurred vision:

• Use of atropine^[1] or other anticholinergics
• Presbyopia—Difficulty focusing on objects that are close. Common in the elderly. (Accommodation tends to decrease with age.)
• Cataracts—Cloudiness over the eye's lens, causing poor night-time vision, halos around lights, and sensitivity to glare. Daytime vision is eventually affected. Common in the elderly.
• Glaucoma—Increased pressure in the eye, causing poor night vision, blind spots, and loss of vision to either side. A major cause of blindness. Glaucoma can happen gradually or suddenly—if sudden, it is a medical emergency.
• Diabetes—Poorly controlled blood sugar can lead to temporary swelling of the lens of the eye, resulting in blurred vision. While it resolves if blood sugar control is reestablished, it is believed repeated occurrences promote the formation of cataracts (which are not temporary).
• Diabetic retinopathy—This complication of diabetes can lead to bleeding into the retina. Another common cause of blindness.
• Hypervitaminosis A—Excess consumption of vitamin A can cause blurred vision.^[2]
• Macular degeneration—Loss of central vision, blurred vision (especially while reading), distorted vision (like seeing wavy lines), and colors appearing faded. The most common cause of blindness in people over age 60.
• Eye infection, inflammation, or injury.
• Floaters—Tiny particles drifting across the eye. Although often brief and harmless, they may be a sign of retinal detachment.
• Retinal detachment—Symptoms include floaters, flashes of light across your visual field, or a sensation of a shade or curtain hanging on one side of your visual field.
• Optic neuritis—Inflammation of the optic nerve from infection or multiple sclerosis. You may have pain when you move your eye or touch it through the eyelid.
• Stroke or Transient ischemic attack
• Brain tumor
• Toxocara—A parasitic roundworm that can cause blurred vision
• Bleeding into the eye
• Temporal arteritis—Inflammation of an artery in the brain that supplies blood to the optic nerve.
• Migraine headaches—Spots of light, halos, or zigzag patterns are common symptoms prior to the start of the headache. An ophthalmic migraine is when you have only visual symptoms without a headache.

Blurred vision may be a systemic sign of local anaesthetic toxicity

• Reduced blinking - Lid closure that occurs too infrequently often leads to irregularities of the tear film due to prolonged evaporation, thus resulting in disruptions in visual perception.
• Carbon monoxide poisoning-Reduced oxygen delivery can effect many areas of the body including vision.^[3] Other symptoms caused by CO include vertigo, hallucination and sensitivity to light.

References

1. Rang, H.P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. p. 147. ISBN 0443071454.
2. Hypervitaminosis A
3. "Carbon Monoxide - Vermont Department of Health". healthvermont.gov. Retrieved 2015-09-18.