Medical Tests & Instruments

By Carmen Willings
teachingvisuallyimpaired.com
​Updated June 13, 2025
To determine how well a child is using their vision, an optometrist or ophthalmologist will conduct a formal eye examination. These exams include a series of vision tests designed to assess a wide range of visual functions.
Tests may evaluate a person’s:
  • Ability to see detail at near and far distances
  • Visual field (central and peripheral vision)
  • Color vision
  • Eye alignment and movement
  • Eye pressure and health of internal structures

Standard Vision Tests and Instruments 

  • Amsler grid test Screens for macular degeneration, a condition affecting central vision. Description: The student views a 4-inch square grid with straight horizontal and vertical lines, along with a black dot in the center, held approximately 14 inches from the face. They are asked to report if they: cannot see the black dot, notice a blank or dark spot, or see any lines as wavy, blurred, or curved.
  • Biomicroscope (Slit-Lamp Exam) Examines the cornea, iris, lens, and vitreous in detail. This instrument projects a thin, intense beam of light into the eye while providing magnification. It allows the eye doctor to evaluate structures that bend and focus light.
  • Confrontation Test Screens for gross visual field loss. The student focuses on the examiner’s nose while the examiner moves a finger or hand from the side toward the center of vision. The student indicates when they see the motion.
  • A keratometer (Also Known as an Ophthalmometer) measures the curvature and shape of the cornea to detect astigmatism. Often used during contact lens fittings or pre-surgical assessments.
  • Ophthalmoscope views the internal structures of the eye, including the optic disc, retina, macula, and choroid.
    • Direct ophthalmoscope: Narrow field of view, higher magnification
    • Indirect ophthalmoscope: Wider view, used in detailed or surgical exams
  • Perimetry Testing (Automated Visual Field Test) assesses peripheral (side) vision. The student looks into a bowl-shaped device while lights flash in different areas. They press a button whenever they detect a light, and a computer maps their visual field responses.
  • Refraction Test determines the need for corrective lenses. After the eyes are dilated with drops, the examiner uses a retinoscope or phoropter to measure how light focuses on the retina. A range of trial lenses is used to identify the most accurate prescription.
  • Tonometer / Tono-Pen Measures intraocular pressure (IOP) to screen for glaucoma or risk of retinal detachment. A tonometer gently touches the anesthetized eye. A tono-pen may use a puff of air or digital touch to record pressure.
  • Visually Evoked Response (VER) / Visually Evoked Potential (VEP) Test Measures how well signals travel from the retina to the brain. The student is shown light flashes while brain wave responses are recorded. This is particularly helpful in diagnosing Cortical Visual Impairment (CVI) or neurological visual processing issues.
  • Tangent Screen Test maps the visual field, especially for central vision loss. The student stares at a target on a black screen with concentric circles. A wand with a target is moved inward, and the student reports when they see it. The examiner records these points to create a visual field map.
  • Visual Acuity Tests measure clarity of vision at near and far distances.  Students identify letters, numbers, or symbols of decreasing size. A Snellen Chart is a standard wall chart with rows of letters, used at 20 feet. An E Chart is used for young children or non-readers. The student points in the direction the E is facing. Design Guidelines for School-Aged Children:
    • Optotypes (letters, symbols) should be equally recognizable.
    • Each line should contain the same number of characters.
    • Horizontal spacing between characters = width of the optotype.
    • Vertical spacing between lines = height of the next smallest optotype.
    • Optotypes should decrease in size by 0.1 log units per row.
    • Black symbols on a white background under good lighting are required.
  • Visual Field Tests detect gaps in peripheral vision. Students fix their gaze ahead while targets are presented in different visual field locations. This test helps diagnose conditions like glaucoma, retinal disease, or brain injury.

Additional Tests and Instruments

  • Optical Coherence Tomography (OCT) A non-invasive imaging test that uses light waves to take cross-sectional images of the retina. It allows the examiner to see each layer of the retina and detect conditions such as macular edema, retinal thinning, or optic nerve damage.
  • Fundus Photography (Retinal Imaging) Takes detailed photos of the back of the eye (retina). These images help monitor retinal conditions such as diabetic retinopathy or macular degeneration over time.
  • Electroretinography (ERG) Measures electrical responses of various cell types in the retina (rods and cones). Useful for diagnosing inherited retinal diseases and some unexplained vision loss.
  • Color Vision Testing (e.g., Ishihara Plates, HRR Plates) Screens for color blindness. The child identifies numbers or shapes hidden within patterns of colored dots. HRR plates can also detect blue-yellow deficiencies and milder cases.
  • Pupil Light Reflex Test Assesses pupil reaction to light to evaluate neurological health and optic nerve function. Abnormal response may indicate optic nerve damage or neurological concern.
  • Ocular Motility and Alignment Testing Evaluates the ability of the eyes to move in all directions (e.g., saccades, tracking, pursuits) and work together. Detects muscle imbalance or nerve palsies affecting eye movements.
  • Stereopsis (Depth Perception) Tests Measures how well the eyes work together to perceive 3D depth. Examples include the Titmus Fly Test and Random Dot Stereo Test.
  • Nystagmus Observation or Testing Identifies involuntary rhythmic eye movements. May be observed in clinic or measured using video nystagmography (VNG) for more detailed analysis.

Unique Vision Testing for Infants and Toddlers ​

Since very young children or those with significant cognitive impairments cannot complete standard vision tests, alternative tools are used to evaluate their visual function.
  • Confrontation Field Test (Pediatric Version) Screens for major gaps in the visual field.
    while they look straight ahead, observers note when and where the child responds to the stimulus.
  • Cover Test Identifies eye misalignment (strabismus). One eye is covered at a time while the examiner watches for movement in the uncovered eye, which can indicate alignment issues.
  • Photoscreening Screens for refractive errors, misaligned eyes, or eye cloudiness. A specialized camera takes images of the child’s eyes, which are analyzed for visual anomalies.
  • Picture-Based Vision Tests (LEA Symbol Chart) measure visual acuity in non-readers. Uses familiar line-drawing symbols (e.g., apple, house, circle) instead of letters. The child points to or names the symbols.
  • The Preferential Looking Test assesses visual acuity in nonverbal or pre-verbal children. Children are shown cards with striped patterns. As the stripes get thinner, the examiner watches to see if the child continues to look at the pattern, indicating they can still see it. The finest visible stripe gives a rough measure of acuity.
History of Visual Impairments
Professional Practice
Vision Professionals
Professionalism
Teacher Resources
Professional Publications
VI Book Resources
Family Resources
VI Referrals
Medical vision exams
visual diagnosis
fvlma
other evaluations