Optometric Terms 4 Flashcards
recovery
the point at which fusion is regained once broken
re-fixation reflex
if you are looking to side of an object instead of directly at it (eg. if you have made an inaccurate saccade, or if a fixated target suddenly moves) it is signaled that the image of the object of regard is blurry, and not viewed straight ahead
re-fixation reflex at the fovea is stimulated as this “error” of eye position is registered, and the eye makes a corrective movement to put the image back on the fovea
reflex allows foveal re-fixation from target to target and maintenance of foveal fixation on a moving target
reticular formation
essential for governing some of the basic functions of higher organisms, and is one of the oldest portions of the brain; part of the brain involved in actions such as:
1) wake/sleep cycle
2) filtering incoming stimuli to discriminate irrelevant background stimuli
3) important regulator in the ANS for respiration rate, heart rate, GI activity, and pain
4) has been shown to play a major role in alertness, fatigue, and motivation to perform various activities
have speculated that the reticular formation controls approximately 25 specific behaviors including sleeping, walking, eating, urination, defecation, and sexual activity
reticular activating system (4)
1) name given to part of the brain (reticular formation and its connections) believed to be the center of arousal and motivation in mammals
2) activity of this system is a prerequisite for consciousness to occur, it is generally assumed that this system’s role is indirect and it does not, by itself, generate consciousness
(instead its unique anatomical and physiological characteristics ensure that the thalamocortical system fire in such a way that is compatible with conscious experience)
3) also involved with circadian rhythm
4) thought to be the area affected by psychotropic drugs
general anesthetics work through their effect on the reticular formation
retinal rivalry
occurs when 2 very different (conflicting) images are simultaneously and separately presented to the two eyes
under normal conditions the brain will alternately suppress one image, then the other
retinoscope
handheld instrument that gives the optometrist info regarding the refractive status of an eye
observation of the retinscopic reflex also provides valuable info regarding attention, visual posture, and embededness of the visual posture
rod
a light-sensitive retinal receptor found in great abundance in peripheral retina
responsible for dim illumination (scotopic) seeing and motion detection
rods transform light info into chemical energy so that it can be used by the visual system
saccades
relatively quick eye movement (compared to the relative slow speed of pursuit movements) during which the eye “jumps” from one target to another
thought to be mediated by the parietal lobe and the eye fields in the frontal lobe
primary stimulus for a saccadic eye movement is
the location of the target
saccades are often called a “ “ movement because
“catching” bc it helps the patient “catch” and bring a new target to the fovea
faster than all the other eye movements and always starts and ends with a fixation
saccades require the patient to have the initial ability of
maintaining fixation
sclera
tough, fibrous white outer runic (coat) of the eye, a continuation forward of the dura mater
what plays a key role in accurate and efficient saccades
thereafter the concept of peripheral awareness and the ability to “calculate” the size of the jump needed to arrive at the desired target
scotoma
area within the visual field in which vision is absent or reduced; may be the result of disease, neurological insult, or prolonged suppression
sherrington’s law of reciprocal innervation
law that explains agonist-antagonist relationships, and monocular eye movements (auctions)
states that when a muscle contracts, its direct antagonist relaxes to an equal extent allowing smooth movement
sight
relates to visual acuity, sharpness of vision, or how well a person is able to resolve letters on the snellen chart, often expressed as a snellen fraction
gives no info as to how much effort is needed to see clearly, to use both eyes together, or how much meaning is obtained from the visual input
SILO
small in, large out
perceived changes induced by the intro of lenses or prisms, target separation, and after-images
single vision
classified as:
- normal: when it is bifocal and there is no manifest deviation
- anomalous: when images of the fixated object are projected from the fovea of one eye and an extrafoveal area of the other eye (i.e. when visual direction of the retinal elements is different)
a small manifest strabismus is therefore always present in anomalous single vision
sphere
a lens with equal power in all meridians
stereopsis
binocular appreciation of depth due to retinal disparity (see also 3rd degree fusion)
eyes are separated in the horizontal plane of the head and thus each eye has a slightly horizontally disparate view of the world
sensory fusion of these horizontally disparate unequal retinal images results in a three dimensional percept
stereoscope
instrument designed to separate the binocular field into 2 parts, one part for each eye
when fusion is attained, a unified image is seen
it is used to explore both binocular and monocular abilities when both eyes are open
brewster (uses sphere-prisms)
wheatstone (uses mirrors)
strabismus
or “squint” or “tropia” refers to the visual condition in which binocular (bi-foveal) fixation is not present
when strabismus is present (manifest) the visual axes of the eyes are not directed toward the same object at the same time
line of sight of one eye does not intersect the target being observed
Streff syndrome
also called “juvenile bilateral functional amblyopia” or the “non-malingering syndrome”
bilateral condition in which there is reduced visual acuity at both distance and near in the presence of minimal refractive error and no evidence of lesion or pathology
visual acuity at near is more reduced than at distance
measured VAs may be variable, and may be better with single letters than with full chart or full line presentation
subjective complaints are usually related to near-point tasks such as reading
frequently patients will have reduced stereopsis, large accommodative lag on dynamic retinoscopy, and a reduced visual field (tubular or spiral field) that may be variable
may be difficulties with eye-hand coordination, fixation difficulties, and color vision disturbances
patient’s general behavior may seem out of step or off in timing
prior to the onset of the condition, most children have been above-average achievers- may be associated with a visual or emotional stress occurring in the child’s life
more prominent during puberty (ages 7-13), girls more frequently than boys
treatment includes low pluss lenses and/or vision therapy
subjective angle
in strabismus, the point at which the patient reports a first degree fusion response or higher
in normal correspondence, the subjective angle of strabismus is equal to or within a few degrees of the objective angle
superior colliculus (SC)
one of the primary processing centers for visual info received from the retina of the eye
a % of magnocellular fibers that leave the back of the eye do not go to the LGN, but instead to the SC in the mid-brain
In the SC, visual info integrates with:
- vestibular info from the semicircular canals
- proprioceptive info from muscles, tendons, and ligaments
- tactile, auditory, and other systems
It is involved in orientation, balance, and postural mechanisms, and keeps the world level.
Part of the process that tells us whether we are moving, the object of regard is moving, or both are moving. Using this info, along with info from other areas of the brain, we construct a personal 3D representation of space, with ourselves placed at the center
