Visual Acuity Purposes: To establish a baseline Legal reasons (driver’s licenses, insurance claim, pension, and disability based on legal blindness) Legal blindness



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Preliminary Testing

  • Visual Acuity

    • Purposes:

      • To establish a baseline

      • Legal reasons (driver’s licenses, insurance claim, pension, and disability based on legal blindness)

        • Legal blindness: 20/200 or worse in better eye OR less than 30 of visual field in the widest meridian of the better eye

      • Monitor progression or improvement of eye disease

      • Guide for the rest of the exam (prediction of refractive error, correlation of data, determines additional testing)

    • Always the first test performed after history

      • Exception: chemical burn/spill; irrigate first, then check VA

    • Definition: the resolving power of the eye, or the ability to see two objects as separate

      • “Normal” resolving power is defined as the ability to detect a gap with a width of 1 min of arc

    • VA is highest at the fovea and decreases with increasing retinal eccentricity

    • VA best if pupil is 2-5 mm

    • Types

      • Minimum Detectable Resolution (minimum visible): the ability to distinguish an object from its background

      • Minimum Separable Resolution (minimum resolvable): the ability to resolve two or more spatially separated targets

        • Gratings, bars, Vernier acuity, preferential looking

      • Recognition Resolution (minimum legible): the ability to recognize letters, numbers, and geometric forms

        • Snellen, Landolt C, Tumbling E

    • Snellen acuity chart is the universal method of measuring VA

      • Snellen optotypes: width of each stroke is equal to the width of a gap on that line

        • “Best” letter is E (3 strokes and 2 gaps)

        • “Not as good” letters are T and L ( no gaps)

      • At 20 feet, a 20 foot optotype subtends 5 min of arc

        • Its details each subtend 1 min of arc

      • 20/20 letter is defined as a letter that has a height (x) such that it subtends 5’ arc at 20 ft

        • Letter height can be altered with test distance

        • Details (gaps and strokes) each subtend 1’ arc at 20 ft

      • Utilizes a “folded” room/operatory system

        • Projector with letters, 2 mirrors and a screen

        • Test distance= patient to mirror + mirror to screen

    • MAR (minimum angle of resolution) in minutes of arc is equal to the reciprocal of the decimal acuity value or the Snellen fraction

      • Snellen fraction = 1/MAR

      • 20 ft (6m) is considered optical infinity, which is defined as the distance at which no accommodation is being used

      • Snellen fraction = testing distance

distance at which the smallest letter read subtends an angle of 5’ of arc

        • Also described as the distance at which a “normal” eye can see the smallest letter read by this patient

    • Snellen equivalent is used when VA is taken at a distance other than 20 ft or when other nomenclature is used

      • It is better to report the actual acuity, not the equivalent

    • Limitations:

      • Number of letters tested per line changes as you move down

      • Letter sizes between lines do not change by a constant ratio

      • Between row and between letter spacing is not proportional to the letter size

      • Legibility for optotypes often varies

    • Standard Chart Specifications

      • Chart luminance: at least 10 foot lamberts

      • Chart contrast: at least 90%

      • Subdued room illumination to enhance chart contrast

        • Uncorrected refractive error is more likely to impact VA when pupils are slightly dilated

    • Distance VA should be performed during ALL patient encounters

      • Procedure

        • Seat patient comfortably and dim lighting

        • VAs taken without correction(sc) and then with correction(cc)

          • Minimizes chance of patient memorizing

        • Clean occluder with alcohol swab

        • Begin with full chart open and ask “Which of these is the smallest line of letters that you can read?”

        • Isolate smallest LOL that the patient can read; continue to scroll down to the next LOL and have patient read it; stop when the patient is unable to read the entire LOL

          • Find the patient’s threshold

        • OBSERVE the patient (no squinting, cheating, leaning forward, etc)

          • Observe the speed and degree of difficulty

        • Record VA as the smallest line in which not more than 2 letters were missed for OD, OS, OU

          • The number at the end of each line signifies the level of acuity

          • Some use several 20/20 lines to minimize memorization

          • “normal” best-corrected VA is 20/20

      • Corrected visual acuity (best corrected VA) is measured with the best refractive correction in place

      • Habitual visual acuity is measured with patient’s own spectacles/CLs

    • Near VA performed during full/comprehensive exam and if they have a near vision complaint

      • Procedure

        • Use full illumination: stand lamp on recording card

        • Done without, then with near correction

        • Measure the distance from the patient’s spectacle plane to the reading card in cm

        • Cover OS and instruct to “Read the smallest paragraph that you are able to”, switch to cover OD, and then remove to read with both eyes open

        • Re-measure the working distance with their correction

        • Record working distance (in meters!) over the smallest print read for OD, OS, OU

      • M system: a 1M letter subtends 5’ of arc at 1 meter

        • Allows patient to hold card at their desired reading distance

      • Reduced Snellen system: gives the appearance of expressing the distance VA that is equivalent to the near VA

        • Should NOT be used for near VA (not appropriate to use a term that suggests a test at 20 ft when that distance is not relevant to near vision)

      • Jaeger system: indicates the size of the print by the letter J followed by a number

        • Poor system because there is no standardization of the Jaeger sizes and there is no intrinsic meaning to the “J” number

    • Pinhole testing: a measure of potential visual acuity

      • Nullifies small amounts of refractive error by 1) increasing the depth of focus and 2) decreasing the size of the blur circles

      • Most effective diameter is 1.32 mm

      • If VA improves with pinhole, suggests that refractive error is probably the cause of the reduced VA

      • Done when entering acuities are 20/40 or worse (based on better VA)

      • Record PH followed by VA obtained

        • If no improvement, record PHNI

      • Super Pinhole, PAM (potential acuity measure) and laser interferometer are commonly used to determine potential VA before cataract surgery

    • Brightness Acuity Test (BAT): used when you suspect acuity would be worse in a glare situation

      • VA with BAT is worse than without BAT for patients who have glare problems

    • Alternative distance VA charts

      • OKN drum: cortical function only; objective test

      • Teller acuity cards: infants, non-responsive patients

      • Tumbling E: preschool, illiterate or non-verbal patients

      • LEA chart: children

      • Allen figures: children

      • Landolt C:

      • HOTV chart: amblyopes

        • Each letter is surrounded by crowding bars

        • Amblyopia: decreased VA (not correctable to 20/20) NOT due to pathology

          • Snellen chart produces contour interactions (slow responses, some correct responses over a wide range of letter sizes, correct end-letter responses, out of order responses, perform better with isolated lines or letters)

      • Feinbloom chart: patients unable to see the 20/400 E on Snellen

        • Full illumination and test distance of 5 or 7 ft

        • Record test distance over smallest number size seen

    • Alternative near VA charts (used during low vision)

      • Bailey-Love Chart: patients unable to see large print on other cards

        • Space between the letters is equal to the letter width (prevents crowding effect)

        • 5 letters on each line

        • Between row spacing is equal to the height of the letters in the smaller row

      • Lighthouse cards

    • Other measures of VA

      • Light perception (performed at ~ 1 ft)

        • LPP: light perception with projection

        • LPO: light perception only

        • NLP: no light perception

      • Hand motion (used as last ditch effort when Feinbloom efforts exhausted)

      • Count Fingers

      • “Fix and follow”: unresponsive patients

        • MUST ALWAYS ATTEMPT TAKING VISUAL ACUITIES

    • Correlation of VA and refractive error

      • General rule: each 0.25DS of uncorrected refractive error accounts for ~ 1 line of Snellen VA

        • For cylinder, take spherical equivalent (sphere + ½ cyl)

        • For oblique axis, add a line for the axis

        • Patient must have NO accommodation or be cyclopleged

  • Pupil Testing

    • Pupil performs 3 primary functions

      • Controls entering light

      • Modifies depth of focus (inverse relationship)

        • Smaller pupil increases depth of focus

      • Varies optical aberrations (smaller has less aberrations)

    • Should be performed during ANY patient encounter regarding eye health

      • Important because it is a neurological test that can detect optic nerve disease, brain mass and aneurysm

      • Gross examination can detect iris abnormalities, media opacities, and leukocoria

    • Shape

      • Pupils should round and centered within the iris on optic axis

      • Irides should be of the same color

        • Abnormalities

          • Corectopia: displaced or misshapen pupil

          • Ectopic pupil: significantly decentered

          • Polycoria: more than one pupil

          • Heterochromia: iris color different between eyes or between different areas in one eye

          • Aniridia: absence of iris, therefore non-existent pupil

    • Size

      • Average of 3.5 mm in adults under normal illumination

      • Become smaller after adolescence due to senile miosis

      • Should equal one another within 1 mm

        • Anisocoria: unequal pupil size

        • 20 % have physiologic anisocoria

      • Controlled by the autonomic nervous system

        • Iris dilator muscle dilates; sympathetic innervation

        • Iris sphincter muscle constricts; parasympathetic innervation

    • Pupillary pathways

      • Afferent

        • Light enters pupil impulse in retina (PR and ganglion cells) optic nerve optic chiasm: ½ cross, ½ ipsilateral optic tracts to superior colliculi pretectal nuclei of hypothalamus crossed and uncrossed fibers to EW synapse with efferent fibers

      • Parasympathetic efferent

        • From EW nucleus travels with CN III (inferior division) cavernous sinus pierces globe deviates from CN III and synapses at ciliary ganglion postganglionic fibers reach iris sphincter via short ciliary nerves

          • 97 % of the fibers control accommodation (ciliary body)

          • Only 3 % innervate the sphincter

      • Sympathetic efferent

        • Hypothalamus synapses at ciliospinal center of Budge (C8-T4) 2nd order neurons leave spinal cord ascending close to the apex of lung synapses at superior cervical ganglion 3rd order neurons follow the ICA’s to the globe iris dilator via the long ciliary nerves

        • Sympathetic innervation reaches Muller’s muscle in upper lids

    • Response to light

      • Miosis (=constriction) occurs via parasympathetic innervation

        • Some latency in initial constriction is normal (depends on brightness and age)

      • Direct response: response that occurs in one eye while the light is shone in that eye

      • Consensual response: response that occurs in one eye while the light is shone in the other eye

      • Pupillary escape: gradual and partial re-dilation without change in light intensity

      • Pupillary unrest or hippus: small oscillations in pupillary diameter that occur during maintained stimulation

        • Due to normal fluctuation in sym/parasym equilibrium

    • Response to near

      • Independent of retinal illumination

      • Near reflex is ALWAYS present when direct light reflex is intact

      • Near triad: pupil constriction, convergence, accommodation

    • Swinging flashlight test

      • Compares the strength of the direct pupillary response with that of the consensual response

      • Detects afferent pupillary defect due to retinal abnormalities or optic nerve pathway anterior to LGN (APD or RAPD)

    • Procedure

      • Remove spectacles and examiner positioned off to one side

      • Use a distant, non-accommodative target (2-3 lines above VA)

      • Measure pupil size under normal lighting conditions

        • Expected findings: should equal one another

          • Size in bright: 2-4mm Size in dark: 4-8mm

        • If pupils are unequal, measure size in both dark and bright light

        • To visualize dark irides, use:

          • Burton lamp: hold ~25 cm (10in) from the patients and below the patient’s line of sight

          • Ophthalmoscope: use as a dim flashlight to illuminate both eyes simultaneously (“light from below”)

      • Judge the roundness of each pupil and describe any abnormalities

      • Observe pupil’s response to light in dim illumination

        • Note the magnitude of change (quantity) using scale 0-3

        • Note the rapidity of reaction (quality) using slow (-) or fast (+)

        • Expected findings

          • Direct response of OD should equal direct response of OS

          • Consensual response of OD should equal consensual response of OS

          • Direct response of OD should equal consensual response of OD

      • Perform the swinging flashlight test

        • Expected findings

          • Rate and amount of constriction should be the same for both pupils

          • Direct should equal consensual for both eyes

        • If it is not the case for either eye: afferent pupillary defect in the eye with less constriction

      • Record using PERRLA (-) APD if all reflexes are normal

        • PE: pupils equal

        • R: round

        • RL: reactive to light (direct and consensual)

        • A: responsive to accommodation

        • (-) APD: no APD

    • Afferent pupil anomalies result in an APD

      • Severe retinal disease, optic nerve diseases or compromise, mass/lesion behind eye compressing optic nerve or chiasm

      • NOT with disorders of ocular media

      • Afferent pupillary defect (RAPD) indicates unilateral or asymmetric damage to the anterior visual pathways

        • When the consensual response is greater than the direct response of one eye

        • If present, pupils of both eyes will constrict less when the light is directed into the affected eye

          • Both eyes will constrict when light beam directed into unaffected eye

        • When light beam is directed in affected eye, causes less constriction in

          • Affected eye: reduced direct reflex

          • Unaffected eye: reduced consensual reflex

        • Graded from trace to 4+

          • 3-4+APD: immediate dilation of the pupil, instead of initial/equal constriction

          • 1-2+APD: no change in pupil size immediately, followed by dilation

          • Trace APD: initial constriction, but greater escape to a larger intermediate size than when light is swung back to normal eye

      • Amaurotic Pupil: severe or 4+APD

        • Patients have an eye with “NLP”

        • Light beam directed into affected eye no direct response in affected eye and no consensual response in unaffected

        • Light beam directed into unaffected eye direct response in unaffected eye and consensual response in affected eye

        • Near reflexes will be intact

      • Reverse (indirect) APD

        • Performed when one pupil is fixed, dilated, or constricted

          • ONLY observe the reactive pupil

        • If APD in eye with reactive pupil, that pupil will constrict more with consensual stimulation than with direct

        • If APD in eye with fixed pupil, the reactive pupil will constrict more with direct stimulation than with consensual

        • Note reverse APD (implies you used a reverse technique)

    • Efferent pupil anomalies: unilateral defects/lesions will often generate anisocoria

      • Anisocoria: usually 2-4 mm difference in dark and light

        • If same degree of anisocoria in light and dark: physiologic

      • Big pupil problems: anisocoria greater under bright conditions due to a defect/lesion of the parasympathetic

        • Adie’s tonic pupil

          • Relatively common; primarily in females 20-40

          • Presentation

            • Unilateral semi-dilated pupil

            • Pupil with minimal and slow reaction to light

            • Pupil with reduced direct, consensual (poor constriction of sphincter) and near responses to light

            • May present with a reduced near vision complaint

            • Vermiform motion of iris: quivering motion of iris at pupillary border due to segmental palsy of sphincter

            • 10-20% eventually affecting other eye

              • Reduced direct response to light bilaterally

              • Decreased near VA

              • Prolonged pupil cycle time

          • Etiology

            • Lesion of the parasympathetic pathway (ciliary ganglion) on the side of the pupil problem

            • Viral

          • Diagnosis

            • 0.125% pilocarpine (wait 10-15 min)

              • Constriction: Adie’s confirmed

              • No constriction: either pharmacologic or 3rd nerve

          • Management

            • Rule other orbital and ocular conditions

            • Cosmesis

            • Accommodation

              • Near add, sometimes unequal adds

              • Equalize accommodation during refraction and other near or binocular testing

              • Accommodation generally returns within 2 yrs

        • Cranial Nerve Palsy

          • Presentation

            • EOM paresis—exotropia and hypertropia (“down and out”) of eye affected

            • Ptosis

            • Fixed and dilated pupil, or non-reactive pupil

          • Etiology

            • Pupil fibers are on the outside of CN III; they are involved early in a compressive lesion and are rarely involved in an ischemic infarction

            • Lesions that involve the pupil: tumor and aneurysm

            • Lesions that spare the pupil: vascular disease causing ischemia (diabetes, hypertension)

          • Diagnosis

            • 0.125% pilocarpine—will NOT constrict

            • 1% pilocarpine—WILL constrict

          • Management

        • Pharmacologic anisocoria: dilation of one eye

          • Presentation

            • Usually unilateral, fixed and dilated pupil

            • Anticholinergic substances block the action of acetylcholine on the ciliary muscle and cause mydriasis

          • Etiology

            • Scopolamine

            • Jimsonweed

            • Antihistamine drops

            • Atropine, homatropine, cyclopentalate

          • Diagnosis

            • 0.125% pilocarpine—Will NOT constrict

            • 1% pilocarpine—Will NOT constrict

          • Management

            • Reassurance and patient education

      • Little pupil problems: anisocoria is greater in dim conditions due to a defect/lesion to the sympathetic nervous system

        • Horner’s syndrome

          • Presentation

            • Miosis (can be mild: less than 1 mm of anisocoria)

            • Ptosis

            • Anhydrosis

***All on the same side as the lesion***

          • Etiology

            • Interruption of the sympathetic system anywhere in its path

            • Congenital Horner’s: idiopathic or trauma at birth

              • Heterochromia and anhydrosis

            • Central lesions: stroke, MS, spinal cord cancer, neck trauma

            • Preganglionic lesions: pancoast tumor, trauma, thyroid enlargement or lesion

            • Postganglionic lesions: extracranial or intracranial cause (Raeder’s, ICA dissection, complicated otitis media)

          • Diagnosis

            • Look at old photographs

            • History of trauma, endardectomy, thyroidectomy?

            • Dilation lag test

              • Take picture immediately after turning off lights and take another picture 15 seconds

              • Horner’s pupil has a dilation lag in the dark of ~15 sec

            • 0.5% Apraclonidine (Iopidine) (wait 15-30 min)

              • Dilates: confirms diagnosis of Horner’s

            • 10% Cocaine drop in affected pupil (wait 15 min)

              • Does NOT dilate: confirms diagnosis of Horner’s

          • Management

            • Important to determine before or after the bifurcation of the carotid artery

            • Differentiate by testing for anhydrosis (prism bar test and corn starch under heat lamp)

              • Postganglionic lesions generally do not cause anhydrosis

              • 1 % hydroxyamphetamine (done 48 hrs after cocaine test)

                • Dilation: central or preganglionic lesion

                • No dilation: postganglionic (“fail safe” affected pupil fails to dilate)



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