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120 Cards in this Set
- Front
- Back
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What is spatial acuity?
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The finest spatial detail that can be detected, discriminated, or resolved
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What is the purpose VA measurements in terms of refraction and prescribing decisions?
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Clinicians use VA charts as targets for refraction procedures to determine if the combination of lenses that yield the sharpest retinal images. This leads to the best VA for the patient. Also comparing entering visual acuity and the visual acuity with new refractive correction.
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What is the purpose of VA measurements in terms of normalcy?
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Most normal individuals have acuities that is better than 20/20. There is a systematic decrease in visual acuity with age. VA is expected to be better than 20/20 at least up to the age of 50. If your patient has a best corrected VA that is worse than 20/20, there is something wrong with some component of their visual system/response. If your patient has a difference in VA of more than 5 letters on a Baley-Lovie chart, further investigation is needed
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What is the purpose of VA measurements in terms of monitoring ocular health?
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VA can be changed due to optical or neural components of the visual system. Monitoring VA can provide a mean of detecting improvement or deterioation in the disorder. A change in the VA is often influential in determining whether the treatment should be initiated, altered, or continued.
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What is the purpose of VA measurements in terms of vision standards?
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Vision standards have been established for many occupations and standard tasks, like driving.
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What is detection acuity?
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AKA minimum visible acuity or minimum distinguishable acuity. It is the angular sie of the smallest visible target.
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What is minimum visible?
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It is the kind of acuity that refers to the ability to detect the presence of objects in the visual field without naming or resolving them. This is equivalent to a detection threshold. It is also an example of brightness discrimination.
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What is minimum perceptible or distinguishable acuity?
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The acuity is the ability to detect fine objects, such as dots or lines against a plain background.
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What is resolution acuity?
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It is minimum separable acuity or minimum resolvable acuity refers to the ability to resolve two or more spatially separated targets (whose visibility is above the threshold separately).
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What is localization acuity?
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Minimum misalighnment acuity or minimum discriminable acuity or hyperability. It refers to the ability to dsicriminate/localize a small displacement of one part of an object with respect to the other parts.
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What are some types of localized acuities?
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Vernier acuity, spatial interval acuity, stereoacuity, and motion acuity
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What is identification acuity?
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The ability to recognize latters, numbers, and geometric forms by resolving their details. Resolution is an important component of identification acuity, but it can also involve other spatial processing. Most tests use in clinical situations are recognition tests
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What is an optoype?
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Test targets
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What are examples of identification acuity?
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Letter optotype
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What are the different types of acuity targets?
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Snellen letters, tumbling E, Landolt rings, Allen optotypes, Low Vision/SOSH, Bailey-Lovie, Lighthouse Contuous text, Wormington Pocket Acuity, HOTV chart, Lea Symbols, Jaeger Card
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What is the international standard (or reference) optotype?
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Landolt rings
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What is the Allen optotype used for?
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Children or illiterates
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What is the Lighthouse Continuous text used for?
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Reading acuity, not single letter acuity
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What are some physical factors affecting acuity?
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Luminance, Contrast, Exposure time, Motion of the target, Optical properties of the eye, and crowding effect
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What are some physiological factors affecting acuity?
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Retinal location, pupil size, accomodation, binocular VA, stiles-crawford effect, fixation, tear film, and psychological
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What is nystagmus?
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The presence of spontaneous oscillatory movements of the eyes. This may lower VA measurements
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What is a latent nystagmus
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A condition that occurs when only one eye is occluded, the unoccluded eye developes the nystagmus and can lower the measured VA. The patient with the nystagmus may have a null point
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When should you suspect hemanopia?
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When there is trouble with the first few letters in each line and it is difficult to locate the start of the next line. Or if there is uncorrected astigmatism (amblyopia) and there is missing several letters in each line
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When should you suspect left hemanopia?
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Left hemanopia is when there is trouble with the first few letters in the line, and possible difficulty finding the start of the line
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When should you suspect right hemanopia?
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When the patient has difficulty advancing to the next letter of each line. The patient may also have a tendency to repeat letters
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When should you suspect amblopia/uncorrected astigmatism?
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When the patient is missing several letters in the line.
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What is the order in visual acuity charts (following the projection)?
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SOSH-->Count Fingers-->Hand Motion-->Light perception with projection-->light perception without projection-->No light perception
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What format is the Wormington Card scientifically designed like?
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Bailey-Lovie
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What is the purpose of the single letter acuity chart on the Wormington card?
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To obtain the patient's single letter visual acuity
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What is the number chart on the Wormington card used for?
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Used with very young children, patients accustomed to a different alphabet, and illiterates
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What is the reading acuity chart used for?
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Assessment of reading ability, however, reading ability is not the same as letter chart acuity
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What is the tumbling E chart used for in the Wormington card?
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For children and illiterates
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What components are found on the Wormington card?
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Pupil measurement, Millimeter ruler, Letter acuity, Tumbling E, Number Acuity, and Reading Acuity
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What are some indications to use the multiple pinhole discs?
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For unexplained visual loss, VA <20/40 OU at distance and near with correction, monocular diplopia, and insufficient working distance with low vision optical aid
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What is a use of a multipile pinhole disc?
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To differentiate between optical and non-optical cause of decreased vision (refractive error vs. corneal abnormality vs. vs lenticular abnormality), to differentiate optical from organic causes of monocular diplopia, to help differentiate lens index differences as the cause of monocular diplopia, to magnify, to determine the type and amount of ametropia, to determine nearpoint of accomodation, to check the final correction, to determine whether any part of the optical system may be used to give useful vision in the case of corneal/lenticular opacities, to function as a therapeutic device, to reveal entoptic phenomena, to increase the worming distance of low vision optical aid, and to predict final visual acuity after cataract surgery
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How does the pinhole work?
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Decreasing the diameter of the blur circles on the retina.
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How much can a pinhole neutralize in RE?
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About 3D in RE.
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If the VA increases with a pinhole, what does this imply?
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Uncorrected refractive error, corneal abnormalities, or lenticular abnormalities
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If the VA does not improve/decreases with a pinhole, what does this imply?
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Further testing is needed (altering light pupil test, color vision, visual field, slit lamp/fundus examination)
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What is the most effective diameter of a pinhole?
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1.32 mm in diameter
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How should the target illumination be with a pinhole?
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the brighter the target, the better the test
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How should the room illumination be when using a pinhole?
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It should be very low during testing, and if possible, the only illumination should come from the acuity chart projection
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With a pinhole, how does it affect retinal illumination?
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Multiple pinholes allow more retinal illumination
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With a high refractive error, how does this affect the blur circles
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The larger blur circles will be even with a pinhole
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How does spectacle correction affect VA with pinhole?
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If the correction corrects the patient's refractive error, the pinhole will either leave the acuity unchanged or slightly degrade it due to diffractive effects.
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What happens when you move the pinhole closer to the cornea
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Increased retinal illumination of the target image and increases field of vision
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How does tilting a pinhole with a thick disc affect VA with a pinhole
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Decrease the effective diameter of the pinhole.
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What do pinholes do?
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Increase depth of focus by decreasing diameter of blur circles, decrease light scattering, decrease aberrations, allow selection of a more normal area of a distorted cornea, and serve as magnifiers
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What is an automated objective refraction?
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It is the refractive error of the eye and the refractive correction without the need of judgment by either the patient or clinician
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What are the uses for autorefractors?
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Preliminary refraction of the patient, screening of children, confirmation of difficult or unusual refractions, refraction of nonverbal or uncooperative patients, and research studies
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What are the categories for automated refractors?
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Manual objective refractors, Automatic objective refractors, Automated subjective refractors, and remote-controlled conventional refractors
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What are the types of automatic objective refractors?
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Without visual acuity capability, with visual capabilities
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What are common characteristics of automated refractors?
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Accomodative control, Wide dioptric range, linearity, pupil limits, speed of testing, use of infared radiation, achievement of end point, nulling vs. open loop principle, and vertex distance
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What is the general procedure of automated refractions?
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Read instructions-->turn it on-->establish initial settings-->establish initial adjustments-->disinfect-->seat patient and make final adjustment-->set/check vertex distance-->give instructions-->adjust to eye-->activate measurement cycle-->obtain readout
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What is precision?
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the closeness of agreement between independent test results and it is usually calculated as the standard deviation of the test results
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What is repeatability?
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The minimum variability between test results
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What is reproducibility?
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The maximum variability of a test result
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Assuming normal distribution of data, what is the repeatability of subjective refraction?
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95% limit of agreement is 1.96 times the SD
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What are reasons for variation in test results?
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Changes in fixation, changes in pupil diameter, changes in accomodation, transient changes in corneal curvature, diurnal variations, inherent variability of instrument/operator, amblyopia, media opacities, keratoconus, unstable tear film, and ptotic eye with long eyelashes
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What is validity or truness?
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Refers to the closness of agreement to between the average value of a large series of results and an accepted reference value. Can be influenced by laboratory bias and bias of the measurement method
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What are some reasons that an individual is unable to obtain readings?
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Small pupils, young age, media opacities, cylinder value outside the range of autorefractor, inability of patient to position head properly, droopy eyelashes/eyelids, improper alignment, posterior segment abnormalities, and inability to maintain steady fixation (ex. nystagmus),
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What are the advantages of autorefraction?
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Increased speed, increased efficiency, delegation of data gathering to technicians, impression of patients with technology
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What are some disadvantages of autorefractors?
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Expensive, and not accurate enough to be relied on for prescription
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What is keratometry?
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Provides information on corneal curvature, and hence on corneal astigmatism
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What are the clinical uses of using a keratometer?
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Objective method of determining the curvature of the cornea, amount and direction of corneal astigmatism, quality of corneal refracting surface, and stability of the corneal refractive surface. It is also used for fitting contact lenses, baseline data, detection and monitoring corneal diseases/conditions, refractive estimation in certain patients (unresponsive, children, amblyopes, high ametropes, patients with media opacitieis), determines nature of ametropia, calculates IOL power, and post-surgical management
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What does the cornea act as?
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A highly convex spherical mirror
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What is the essential components of a keratometer?
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Object, Magnify device, Doubling systems for focusing and for measuring the image size (thus radius of curvature)
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What are the two keratometer types?
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One position and two-position
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What is the procedure in using keratometer?
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Seat patient-->explain the test to patient-->focus eyepiece-->unlock instrument controls-->disinfect-->adjust patient-->alight instrument (while looking from outside)-->instruct patient-->focus and perform fine alignment (adjust axis) -->lock instrument-->adjust horizontal and vertical power drums until the mires overlap-->measure radius and power in horizontal meridian-->measure radius and pwoer of vertical meridian-->repeat for other eye
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What are the types of astimatism?
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Irregular (distorted mires), regular (WTR/ATR), and oblique
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What is WTR astigmatism?
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More power in the vertical meridian (greatest curvature), and hence the horizontal meridian is flatter
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What is ATR astigmatism?
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More power in the horizontal meridian (greatest curvatre), and hence the vertical meridian is flatter
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What is oblique astigmatism?
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The principle meridians are between 30 to 60 and 120 to 150
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What are the sources of error when using a keratometer?
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Improper calibration, faulty positioning of patient, lack of proper fixation forgetting to focus eyepiece, not centering ht mire images, not determining the correct axis, reduced acuity of examiner, accomodative fluctuation by examiner, localized corneal distortions, lacrimal fluid, and lid position, improper focusing of the corneal image, and drooping of patient's eyelids
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What is the basic concepts in using an NCT?
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Estimate IOP by having a puff of air flatten the cornea to measure the time from internal reference point to the flattening period and converting it into an IOP value
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What are some source sof error/variability in IOP measurement with NCT?
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Ocular pulse, Blinking, Off-center misalignment, and irregular cornea
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What is the technique of using an NCT?
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Seating patient-->align patient-->ask patient to look at the end of the nosepiece and look at fixation light-->have patient lean with forehead-->Ask patient to blink before measuring-->Measure->Measurement will be made in sequence
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What is the purpose of a Frequency Doubling Technique (FDT)?
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For screening and thresholding the central visual field
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What are the target stimuli for FDT?
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Sinusoidal grating, background illuniation of 100 cd/m2, contrast range of 56 dB, interstimulus interval of 0 to 500 ms, area testing of 20-30 degrees, and 17 FDT patterns
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Why use nonlinear lines?
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Most ganglion cells respond to linearly to contrast, however, a subset of M-cells react to nonlinearity. This causes spatial frequency doubling
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What are the tests that are available for FDT?
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C-20-1 test which has high specificity due to liberal limit for normality. Thi sis useful for screening large populations because it reduces the number of patients falsely classified as having abnormal vision, and the C-20-5 test which has a higher sensitivity and should be used in clinical setting and has greater emphasis on detecting the earliest signs of visual field dysfunction.
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What are fixation errors?
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The ratio of the number of times the patient responded to a target placed in the blind spot vs. the total number of times fixation was tested
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What are false-positives?
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The ratio of the number of times the patient responded to a pause int eh testing sequence vs the total number of pauses in the testing sequences
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What are false negatives?
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The ratio of the number of times the patient did not respond to a target pattern at the maximum possible contrast level of the instrument vs. the total number of times the maximum possible contrast level patterns were tested
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What are Ganzfeld blankouts?
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The fading or darkening of vision in the eye being tested. This has little effect on detectability of the targets. This can be avoided with blinking repeatedly for a few seconds.
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What is the procedure in using an FDT?
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Turn the instrument on-->remove calibration cap-->select "Run Patient Test"-->enter patient's age and select "Accept Setting"-->Slide patient's visor to right eye-->repare patient-->determine if patient should have habitual Rx-->Explain test procedure-->Choose right setting-->monitor display-->begin test-->slide visor-->begin test-->print test
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When should a patient use their habitual Rx?
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The patient should wear their Rx since the target is at optical infinity. No photochromatic lenses
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Color vision depends on the integrity of what?
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Retinal cones, and afferent visual pathways
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What are causes of defective color vision?
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Heredity or Acquired (due to disease/trauma, or drug toxicity)
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What are the heredity causes for defective color vision?
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Abnormality or absence of one or more of the 3 cone types
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What are the classifications of the color vision disorders?
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Monochromats, Dichromats (Protanopia, Deuteranopia, and Tritanopia), and Trichromats (Protanomalous, Dueteranomalous, and Tritanomalous)
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What are the two forms of the color vision test?
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Ishihara--does not screen blue/yellow and Hardy-Rand-Rittler, which does screen blue/yellow defects
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What do color vision tests assess?
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Identification of numbers/letters/shapes, arranged colored targets in an orderly spectral sequence, matching colors
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What are the test conditions for an Ishihara test?
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VA must be 20/200 or better, good illumination (must wear C-Daylight Glasses with filter), testing distance has to be 75 cm, plates are held perpendicular to the line of sight, plates are shown for 3 seconds, doctor/clinician turns the plate, monocular
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What is sequence of Ishihara
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#1-Everyone must see (catch malingerers/hysterics), #2-15 screening plates (Transformation #2-7, vanishing #8-13, hidden digit design #14-15), #16-17-diagnostic plates, #18-24-illiterates (use camel hair brush to trace)
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What is the criteria in errors for Ishihara test?
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<4 errors--normal, >5 errors--failure (follow up needeD)
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What are the testing conditions for HRR pseudoisochromatic plates?
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VA must be 20/200 or better, good illumination (must wear C-Daylight Glasses with filter), testing distance has to be 75 cm, plates are held perpendicular to the line of sight, plates are shown for 3 seconds, doctor/clinician turns the plate, monocular
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What is the sequence of HRR?
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#1-4 demonstration plates (not scored), #5-10-screening plates. Any failures will move on to the appropriate diagnostic plates?
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What do the diagnostic plates represent?
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Plates #11-24 are used
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What is red/green deficiency?
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Protan/Deutan
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What is blue-yellow deficiency?
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Tritan/Tetartan
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What is stereopsis?
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The perception of nearness or farness of object points obtained from disparate, but fusible, retinal image. It is the smallest amount of horizontal retinal image disparity that gives rise to a sensation of relative depth, and it is measured in seconds of arc
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What is the purpose of testing steroacuity?
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To evaluate the presence/absence and degree of steropsis. It is also used to indirectly measure suppression, it can screen for constant strabismus or monofixation. It can determine suitability for certain professions, aid in the treatment of patients with binocular anomalies, and to aid in prediciting the prognosis for successful treatment of binocular anomalies
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What are some impairments in performance of stereoacuity?
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Reduce VA or blur in one eye or OU, bifoveal misalignment, small supression or scatoma, or aniseikonia
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What are the two types of targets in Randot stereotesting?
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Contour targets, which is used to assess contour/local stereopsis and Random-dot stereotargets which is used to assess global steropsis
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What are the 3 subtests of stereotesting?
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Forms, animals, and circles
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Is stereotesting performed monocularly or binocularly?
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Binocularly
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What are the criteria for passing stereotesting?
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40 seconds of arc and correctly identifying forms
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What can enhance appreciation of stereopsis?
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Gentle side-to-side rocking of the test will induce binocular parallax, and may help the patient appreciate the steropsis, rotating 90 degrees will reverse disparity
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What is near point of convergence (NPC)?
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Point closest to patient where patient loses binocular fixation and haplopia (subjective endpoint). It is also the point closes to the patient at which the lines of sight intersect at the target
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What is the purpose of NPC?
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To assess the patient's convergence amplitude?
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What is the target of NPC?
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A small, non-detailed light source, or a light source and red filter.
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Where is the target initially held relative to the patient during NPC?
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40 cm from patient and then 15 cm below horizontal
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What is the break period during NPC?
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The point in which non-dominant eye turns out or where the patient reports diplopia
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Where is the recovery during NPC?
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That point where the patient reports singleness again or when patient regains bifoveal fixation
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What are some causes of receded NPC?
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Convergence insufficiency or convergence paralysis
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What are some characteristics of pursuits?
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Conjugate slow eye movement, controlled by occipito-parietal junctions, mediated by cerebellum and vestibular nuclei, pursuit defects, and pursuits testing techniques
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What shape should pursuits be tested as?
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Broad H-shape
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What are some things to look out for during pursuit testing?
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Smoothness, accuracy, and restrictions of gaze.
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Where/Who can pursuit defects occur in?
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Children <6 years old, hyperactive children, nervous patients, and patients on tranquilizers.
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