Visual Acuity and Color Blindness Testing Procedures

Visual Acuity Tests

Measure lens ability to focus light on retina.

Central Fovea

Area of retina for sharp central vision.

Refractive Power

Lens ability to bend light rays.

Emmetropic

Normal vision for distance and near.

Hyperopic

Farsightedness; normal distance, blurry near vision.

Myopic

Nearsightedness; blurry distance, normal near vision.

Presbyopia

Age-related decrease in lens accommodation.

Near Point of Vision

Closest distance to focus on an object.

Snellen Acuity Card

Tool for measuring near visual acuity.

20/20 Vision

Normal vision; sees at 20 feet what is normal.

20/40 Vision

Sees at 20 feet what normal sees at 40 feet.

20/15 Vision

Sees at 20 feet what normal sees at 15 feet.

Blind Spot

Area in retina lacking photoreceptors.

Astigmatism

Blurriness due to irregular lens or cornea shape.

Red-Green Color Blindness

Common inherited disorder affecting color perception.

Cone Distribution

64% red, 34% green, 2% blue cones in retina.

Photopigments

Molecules in cones that detect light wavelengths.

Color Perception

Activation of cones differentiates colors.

Normal Color Vision

Ability to perceive all colors accurately.

Total Color Blindness

Inability to perceive any colors.

Visual Acuity Measurement

Determining clarity of vision using charts.

Distance Visual Acuity

Measured at 20 feet using Snellen chart.

Near Visual Acuity

Measured at 14 inches using Snellen card.

Clinical Note

Record missed letters for accurate vision assessment.

Testing Procedure

Cover one eye and read smallest line.

Measurement of Blind Spot

Distance from face when dot disappears.

Light Source

Illumination necessary for visual acuity tests.