Near visual acuity

Measurement of the clarity of vision at close distances

Near visual acuity refers to the clarity or sharpness of vision when viewing objects at a close range, typically at a distance of 35 cm to 50 cm. This is an important aspect of visual acuity that is crucial for tasks such as reading, writing, and other activities that require detailed vision at close proximity.

Measurement

Near visual acuity is commonly assessed using a variety of charts and tests designed to evaluate how well a person can see objects at a close distance. These tests are often conducted in a clinical setting by an optometrist or ophthalmologist.

N notation reading chart

Near Vision Charts

One of the most common methods for assessing near visual acuity is the use of near vision charts. These charts typically contain rows of text or symbols of decreasing size, which the patient is asked to read aloud. The smallest size that can be read accurately determines the near visual acuity.

• Snellen Near Vision Chart: Similar to the Snellen chart used for distance vision, the Snellen near vision chart uses letters of varying sizes to assess near vision. The results are often recorded in a fraction, such as 20/20, indicating normal near vision.

Snellen's near vision chart

• Jaeger Chart: This chart uses paragraphs of text in different sizes, labeled with "J" numbers, to determine near visual acuity. The smallest paragraph that can be read comfortably indicates the acuity level.

• N Notation: This system uses numbers to denote the size of the text, with "N5" being smaller than "N10". It is often used in clinical settings for its simplicity and ease of use.

Testing Procedure

During a near visual acuity test, the patient is typically seated in a well-lit room and asked to hold the chart at a specified distance, usually around 40 cm. The examiner may use a phoropter or trial lenses to determine if corrective lenses are needed to improve near vision.

Factors Affecting Near Visual Acuity

Several factors can influence near visual acuity, including:

• Age: As people age, they often experience presbyopia, a condition where the eye's lens loses flexibility, making it difficult to focus on close objects.

• Refractive Errors: Conditions such as myopia, hyperopia, and astigmatism can affect near vision clarity.

• Lighting Conditions: Adequate lighting is essential for optimal near vision. Poor lighting can strain the eyes and reduce visual acuity.

• Eye Health: Conditions such as cataracts, glaucoma, and macular degeneration can impair near vision.

Improving Near Visual Acuity

Corrective lenses, such as reading glasses or bifocals, are commonly prescribed to improve near visual acuity. In some cases, contact lenses or refractive surgery may be recommended.

Diagram of eye focusing

Related pages

• Visual acuity
• Presbyopia
• Optometry
• Ophthalmology