A visual acuity test chart that uses rings with a gap to determine the direction of the gap, allowing for assessment of visual acuity.
A visual acuity of 20/200 to 20/400 indicates severe low vision, which is considered legal blindness by US definition. Individuals at this level can generally orient and move but may have difficulty with traffic signs and reading without high-power magnifiers.
A refractive error where distant objects appear blurry while close objects can be seen clearly, often referred to as nearsightedness.
A visual acuity of less than CF 4 ft indicates nearly total blindness, where vision is unreliable except under ideal circumstances, and individuals must rely on non-visual devices.
Legal blindness is defined as severe visual impairment in both eyes, which is often used to determine eligibility for disability benefits.
Pseudoisochromatic color plates are a set of multicolored dot patterns used to evaluate color vision, where patients with normal color vision can easily detect specific numbers and figures embedded in the pattern, while those with impaired color vision may not.
Pitfalls include ensuring that all lenses, projectors, and charts are clean, paying attention to distances and calibrations for each type of acuity screen, avoiding glare on the viewing chart or in patients' eyes, and using appropriate tests for the patient's abilities.
The NPC is the point where a single image can no longer be maintained, noted when the image doubles or one eye deviates from the fixation target.
Using habitual correction allows the patient to see as clearly as possible during the test, providing a more accurate assessment of their visual acuity.
Recording acuity values for each eye separately allows for a detailed assessment of visual function and helps identify any discrepancies in vision between the two eyes.
The procedure involves the patient wearing their habitual corrective lens, holding a near card at a specified distance, occluding one eye at a time, and reading the smallest legible characters, with acuity values recorded for each eye and binocularly.
Occluding the eye not being tested helps to isolate the visual function of the eye being assessed, ensuring accurate measurement of visual acuity.
A condition where the eyes do not work together properly while focusing on a nearby object, affecting binocular visual acuity.
'20/40 − 2' indicates that the patient was able to read the 20/40 line but missed 2 letters on that line.
Retesting acuity with both eyes simultaneously helps to assess the combined visual function and can provide a more comprehensive understanding of the patient's overall visual acuity.
Testing methods for toddlers and preliterate children include picture charts, Lea symbols, the Landolt C or tumbling E test, and the HOTV chart.
'OU' represents 'both eyes (together)', indicating that the visual acuity measurement is for both eyes simultaneously.
The NPA is the point (in centimeters or inches) where the patient can no longer bring the image into clear focus.
The procedure involves placing a near testing card at 16 inches from the patient, asking them to read a specific line, moving the card closer until the letters blur, and recording that distance.
The procedure involves holding a target at approximately 16 inches from the patient, moving it closer until the image doubles, and observing eye convergence.
To occlude the left eye means to cover it with an occluder to prevent vision, ensuring that only the right eye is tested for visual acuity.
Tear film abnormalities, such as dry eye syndromes, can decrease visual acuity, but their effects can be minimized by the generous use of artificial tear preparations.
Latent nystagmus is a condition that occurs only when one eye is occluded, causing the unoccluded eye to develop nystagmus, resulting in lower measured visual acuity compared to binocular acuity.
Presbyopia refers to the condition where the near point of accommodation recedes with age, making it difficult to focus on close objects.
The normal range for the near point of convergence (NPC) is between 6 cm and 10 cm, regardless of a person's age.
Visual impairment refers to a condition where a person cannot achieve normal vision (20/20) even with optical correction such as eyeglasses or contact lenses.
Severe visual impairment is characterized by corrected distance visual acuity being less than 20/160, including ranges from 20/200 to 20/400.
The crowding phenomenon refers to the tendency of amblyopic patients to identify smaller optotypes more easily when viewed singly rather than in a line with figures on both sides.
Glare occurs when light from a single bright source scatters across the visual field, reducing the quality of the visual image and potentially causing distorted vision.
The 15-hue test, also known as the Farnsworth-Munsell D-15 test, consists of 15 pastel-colored chips that patients must arrange in a related color sequence, which is obvious to those with normal color vision but challenging for patients with color deficits.
If the pinhole improves the patient's acuity by 2 lines or more, it suggests that the patient likely has a refractive error, as the pinhole allows for better light entry without the need for refraction by the cornea or lens.
A patient's preferred reading distance can vary based on the types of near activities they engage in and whether they use near spectacles.
Corneal or lenticular astigmatism might necessitate the use of special spectacle or contact lenses to correct the visual impairment.
Snellen acuity measures the resolving ability of the eye using targets that subtend a visual angle of 5 minutes of arc.
Visual acuity is an important factor used by examiners to estimate a patient's potential disability and to determine appropriate reading aids and distances.
The Pinhole Acuity Test is a method used to assess visual acuity by having the patient read a testing chart through a pinhole occluder, which allows only central rays of light to enter, helping to determine if reduced visual acuity is due to a refractive error.
Using different charts or optotype sequences is important because patients may memorize the sequence of images they have seen multiple times, which can affect the accuracy of the test results.
The Snellen acuity expression represents the distance at which a patient can read a specific line of optotypes, with the numerator indicating the distance from the chart and the denominator indicating the size of the optotype read correctly.
Visual acuity is recorded with a superscript notation indicating the number of letters missed, for example, 20/40 − 2 if two letters are missed on the 20/40 line.
CF stands for 'counting fingers,' which is used to record the longest distance at which a patient can accurately count fingers displayed by the examiner.
NLP stands for 'no light perception,' indicating that the patient cannot perceive any light.
'cc' stands for 'with correction', indicating that corrective lenses were worn during the visual acuity test.
Measurement notation provides a standardized way to express visual acuity measurements, facilitating communication and documentation.
A method of testing visual acuity where the patient looks through a pinhole occluder to determine the sharpest image they can see on a distance chart.
A condition associated with aging that results in a gradual loss of the eye's ability to focus on nearby objects.
A condition where the eye has difficulty focusing on near objects due to inadequate accommodation.
For profound visual impairment (20/500 to 20/1000), limited spot reading with visual aids is possible, and high-power magnifiers are typically required.
Horizontal OKN should be present by 3 months of age, indicating normal visual development and the ability to track moving objects.
Low-vision testing aims to assess the visual capabilities of patients who cannot read the largest line on a standard visual acuity chart, often by using shorter distances or alternative methods to measure acuity.
Profound visual impairment is defined as corrected distance visual acuity being less than 20/400, which includes ranges from 20/500 to 20/1000.
One minute is the smallest angle discernible for normal human vision.
Amblyopia is a visual disorder characterized by a difference in optically correctable acuity of more than 2 lines between both eyes, resulting from abnormal visual input in early childhood. It is commonly referred to as 'lazy eye.'
For a visual acuity of 20/80 to 20/160, strong reading glasses or vision magnifiers are recommended, as they usually provide adequate reading ability, although this level is typically insufficient for a driving license.
The letter L is the easiest letter to recognize during visual acuity testing and can be mistaken for few letters other than the letter I, making misinterpretation of other letters, like B, less significant.
The term 'blindness' should be avoided because most patients with severe visual impairment have some useful vision, and many demonstrate significant resourcefulness.
Common abbreviations include C, S, M (central, steady, maintained fixation) and F & F (fixes and follows), which are used for preverbal or nonverbal children.
Neurologic factors such as visual field defects, optic nerve lesions, pupillary abnormalities, and impairment by drugs can all influence visual acuity testing.
Most states require visual acuity to be correctable to 20/40 or better in at least one eye for an unrestricted driver's license.
For patients unable to resolve the largest optotype, they should be positioned 10 feet from a well-illuminated test chart, with the eye not being tested occluded, and the testing distance halved until they can identify half the optotypes on a line.
Dirty lenses of any kind, whether trial lenses, phoropter lenses, eyeglass lenses, or contact lenses, will decrease acuity, resulting in falsely low measurements.
Patient fatigue or boredom can affect acuity measurements, making it difficult to assess their true visual acuity.
Motility defects such as nystagmus or other movement disorders can interfere with the ability to align the fovea on the object of regard, leading to lower acuity measurements.
The near point of convergence (NPC) is the nearest point to which both eyes can converge and still maintain a single image.
LP indicates that the patient can perceive light, and it can be further specified as 'LP with projection' or 'LP without projection' based on the patient's ability to identify the direction of the light.
A small toy or other sight-stimulating object that does not produce sound, held about 1–2 feet from the infant's face.
An occluder is used to cover the eye that is not being tested, ensuring that only one eye is evaluated at a time for accurate measurement.
'NPA' stands for 'Near Point of Accommodation', which refers to the closest point at which the eye can focus on an object.
Unilateral amblyopia is a condition where one eye has reduced vision due to causes such as anisometropia, strabismus, or unilateral media opacities like congenital cataracts.
Contrast sensitivity measures the ability to discern relative darkness and brightness, as well as the ability to see details, edges, and borders of images.
Color vision differences between two eyes may indicate optic nerve or retinal disease, with common abnormalities including X-linked congenital red-green deficiencies.
The HOTV optotypes are symmetric, useful for matching, and particularly effective for nonverbal or illiterate patients, making them suitable for testing young children.
Optokinetic Nystagmus (OKN) is a reflexive eye movement that can be elicited by moving a regularly striped object in front of a viewer, indicating the ability to discriminate detail.
The pinhole test is used to recheck visual acuity when it is worse than 20/20, helping to determine if the reduced acuity is due to refractive error or other factors.
HM stands for 'hand motion,' which is recorded when a patient can detect the examiner's hand movement at a specified distance.
Visual acuity refers to an angular measurement that relates testing distance to the minimal object size resolvable at that distance.
Moderate visual impairment is defined as corrected distance visual acuity (best-corrected VA) being less than 20/60, which includes ranges from 20/70 to 20/160.
A 20/20 visual acuity is considered normal visual acuity, meaning the individual can see at 20 feet what should normally be seen at that distance.
PH signifies the acuity obtained using the pinhole test, indicating that the measurement was taken while the patient was looking through a pinhole occluder.
The Testing Distance Visual Acuity protocol involves asking the patient to stand or sit at a designated distance (ideally 20 feet) from a well-illuminated wall chart, occluding one eye, and having the patient identify letters or objects on successively smaller optotypes until a certain threshold is reached.
Lighting conditions must remain equivalent for acuity tests to be comparable, as variations can influence visibility and accuracy of measurements.
When interacting with patients who have low vision or are blind, it is important to alert them to your movements beforehand, offer an arm for guidance without grabbing, and use a demeanor and testing approach appropriate for their age.
The near point of accommodation (NPA) is the nearest point at which the eye can focus to form a clear image on the retina.
The crowding phenomenon refers to the effect where the presence of nearby letters or objects makes it more difficult for a patient to identify a target, enhancing sensitivity for detecting amblyopia.
A visual acuity notation that expresses visual acuity as the logarithm of the minimum angle of resolution, with acuity of 20/20 having a logMAR value of 0.
The Prince or RAF rule is used to convert measurements of the near point of accommodation (NPA) expressed in meters into diopters.
The Pinhole Acuity Test is used to determine if a patient's vision can improve with pinhole occlusion, helping to differentiate between refractive errors and other vision issues.
Before conducting a visual acuity examination, it is important to determine if the patient is familiar with the optotypes being used and to choose the appropriate chart based on the patient's comfort with letters or numbers.
The Near Acuity Test assesses a patient's ability to see clearly at a normal reading distance, taking into account their preferred reading distance and any near spectacles they may use.
A conversion of the Snellen fraction to a decimal format, where Snellen 20/20 equals decimal 1.0, Snellen 20/30 equals decimal 0.7, and Snellen 20/40 equals decimal 0.5.
Jaeger notation, also referred to as number acuity, is a system used to indicate near visual acuity on test cards.
Fixation preference testing is a method used to detect amblyopia in preverbal children by observing which eye the child prefers to use when both eyes are tested separately.
If a chart is not kept clean, smaller letters become more difficult to identify, potentially leading to falsely low acuity measurements.
A Rosenbaum pocket vision screener is a tool used to test near visual acuity, often utilized in clinical settings.
The Distance Acuity Test is a vision test performed to measure a patient's ability to see at a distance, typically conducted with and without corrective lenses.
A method to express near visual acuity by assigning arbitrary numbers to Snellen equivalent figures.
'sc' indicates 'without correction', meaning the visual acuity test was performed without the use of corrective lenses.
Optotypes are targets used in visual acuity testing that subtend a visual angle on the retina, typically consisting of letters or symbols.
A method of recording visual acuity by indicating the distance at which a patient can read a specific line on an eye chart, expressed as a fraction (e.g., 5/80).
A visual acuity notation that quantifies visual discrimination of fine detail, represented as a fraction where the numerator indicates the distance at which the test is performed and the denominator indicates the distance at which a subject with unimpaired vision can read the same figure.
Allen reduced picture cards are used to test near visual acuity in children.
An individual letter, number, or picture on a testing chart used in visual acuity testing.
External factors such as patient distraction, fatigue, age, and psychological influences can affect the results of visual acuity measurements.
The ATS visual acuity testing protocol uses isolated HOTV optotypes surrounded by bars and is gaining acceptance for testing young children due to its high testability and excellent test-retest reliability.
In cases of suspected latent nystagmus, the fellow eye may be blurred using a +10.00 to +20.00 diopter lens instead of a standard occluder to obtain the best possible monocular visual acuity.
The Snellen fraction is a notation used to express visual acuity, represented as a ratio of the distance at which a patient can read a specific line on a visual acuity chart to the distance at which a person with normal vision can read the same line.
The number in the denominator represents the distance at which the target subtends a visual angle of 5 minutes of arc.
Teller acuity cards are large photographic plates used to estimate visual acuity in infants, featuring line gratings that become progressively smaller, allowing the examiner to determine the baby's direction of gaze.
A consistent blink response to a bright light, even through closed eyelids, is an indicator of normal visual function in newborns.
Children may prefer different types of visual acuity charts because some respond better to numbers while others prefer letters, and their engagement can affect testing accuracy.
To assess the infant's visual tracking and fixation abilities by observing their eye movements in response to a visually stimulating object.
Patients with extremely low vision, including infants, toddlers, illiterate adults, and nonverbal patients, require special testing methods and attention to accurately assess their visual acuity.
Testing the right eye first is a convention in visual acuity testing to maintain consistency and avoid confusion in the testing routine.
stripe
near
optotype
distance
details
optotypes
missed
1
10
numbers
clean
2
Snellen
2.4
distance, near
abnormalities
clear
20/200, 20/400
left, right
Hand
to the ceiling
Rosenbaum
L
external, internal
legible
optotypes
touch or press
crowding
optic
B
1.0
treatment
eyes
right
20/500, 20/1000
16
PH
16
numbers
Farnsworth-Munsell D-15
tumbling E
anisometropia
striped
cc
contrast
fatigue
tear film
Allen
sc
6
United States
image
optotypes
special
shorter
reading
denominator
equivalent
blurred
crowding
lazy
6, 10
Near
CF
light
3
suspected
disability
sharpest
test
low
20/12, 20/25
lower
occluders
contrast
lateral geniculate nucleus, visual cortex
Snellen
recognizable
near
20/40
separately
resolution
1.0
accommodation (NPA)
16
Visual
another
chart
numerator
parent
sound
20/160
habitual
spectacle, contact
20/20
nystagmus
2
refractive errors
3
20
+10.00 to +20.00
presbyopia
count
distance
numerator
bite
presbyopia, premature
multicolored
20/80, 20/160
one
doubles
differently
simultaneously, OU
sequences
deficiencies
pinhole
refractive
movements
similar
blindness
gradual
tumbling
LP
chart
binocular
bars
20/20
−
20/400
HM
20, 20
separately
20/60
NLP
symmetric
20/40
blink
fixation
color
3, 1
140°
nonverbal