Reduced visual acuity (RVA) means a person’s vision is worse than the established standard for normal, even with corrective lenses. This decrease in the sharpness or clarity of sight significantly impacts daily tasks like reading, driving, or recognizing faces. Since RVA causes range from easily correctable issues to serious underlying diseases, any noticeable decline warrants professional attention and an examination from an eye care professional.
Understanding Visual Acuity Measurements
Visual acuity measures how clearly one sees fine detail at a specific distance, typically quantified using the Snellen chart. Vision is expressed as a fraction, where the first number represents the distance the person stands from the chart (usually 20 feet). The second number indicates the distance at which a person with standard vision could read the smallest line the patient successfully read.
For instance, 20/20 is the benchmark for normal vision. A measurement like 20/40 signifies RVA, meaning the person must stand at 20 feet to see what a person with normal vision can see from 40 feet away. In countries using the metric system, the standard is expressed as 6/6.
Common Structural Causes
The most frequent causes of RVA are refractive errors, structural issues preventing light from focusing precisely onto the retina. These errors, often due to the shape of the eyeball or the cornea’s curvature, cause light to bend incorrectly but are typically correctable with lenses.
Myopia (nearsightedness) occurs when the eyeball is too long or the cornea is too curved, causing light to focus in front of the retina and blurring distant objects. Conversely, hyperopia (farsightedness) happens when the eyeball is too short or the cornea is too flat, causing light to focus behind the retina and making close objects harder to see clearly. Astigmatism involves an irregular curvature of the cornea or lens, leading to uneven light scattering and distorted vision at all distances. Another structural cause is a cataract, where the normally transparent lens becomes cloudy, physically obstructing light passage to the retina.
Underlying Progressive or Disease-Related Causes
Beyond simple structural issues, RVA can be a symptom of more severe, progressive diseases that affect the internal components of the eye.
Age-Related Macular Degeneration (AMD)
AMD is a leading cause of vision loss in older adults, damaging the macula, the central area of the retina responsible for sharp, straight-ahead vision. The dry form, the most common type, involves the gradual formation of yellow protein deposits called drusen under the macula. The wet form involves the growth of fragile, abnormal blood vessels that leak fluid and can cause rapid vision loss.
Glaucoma
Glaucoma causes progressive damage to the optic nerve. This damage is often linked to abnormally high intraocular pressure inside the eye. Untreated glaucoma can lead to irreversible loss of peripheral vision and, eventually, central vision.
Diabetic Retinopathy
Diabetic retinopathy is a complication of diabetes where high blood sugar levels damage the tiny blood vessels in the retina. This damage can cause vessels to swell and leak fluid, leading to blurred vision. It can also trigger the growth of new, fragile vessels that bleed into the eye, causing scar tissue formation and retinal detachment.
Optic Neuritis
Optic neuritis involves inflammation of the optic nerve, which slows or blocks the transmission of electrical signals to the brain. This results in a sudden reduction in vision, pain with eye movement, and loss of color vision. This condition is often associated with systemic inflammatory diseases, such as multiple sclerosis, and requires careful medical investigation.
Diagnostic Procedures and Examinations
Determining the specific cause of RVA requires a comprehensive eye examination. The process begins with refraction testing to measure any refractive error and determine the best-corrected visual acuity. Specialized diagnostic procedures are used to examine both the front and back structures of the eye:
- A slit-lamp exam uses a microscope and bright light to closely examine the front structures, including the cornea, lens, and iris, helping identify conditions like cataracts.
- Tonometry measures the pressure inside the eye, which is used to screen for and manage glaucoma.
- A dilated eye exam allows the doctor to inspect the retina and optic nerve for signs of damage caused by conditions like diabetes or AMD.
- Advanced imaging tests, such as Optical Coherence Tomography (OCT) and retinal photography, provide detailed cross-sectional images of the retina and optic nerve, aiding in the diagnosis of subtle structural changes.
Correction and Management Strategies
Strategies for addressing RVA depend entirely on the underlying cause, falling into two main categories: correction and medical management.
Correction
For structural causes like refractive errors, primary solutions involve corrective lenses (eyeglasses or contact lenses) that adjust how light focuses on the retina. Refractive surgery, such as LASIK or PRK, offers permanent correction by reshaping the cornea. Cataract surgery is also corrective, involving the removal of the cloudy natural lens and replacement with a clear, artificial intraocular lens.
Medical Management
When RVA stems from progressive diseases, the focus shifts to medical management to control the condition and prevent further vision loss. Glaucoma is often managed with prescription eye drops to lower intraocular pressure, sometimes requiring laser procedures or surgery. Diabetic retinopathy may be treated with laser procedures to shrink abnormal blood vessels or injections of anti-VEGF medication to reduce macular swelling. If RVA cannot be fully corrected, low-vision rehabilitation and devices, such as specialized magnifiers, help patients maximize remaining vision and maintain functional independence.