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88 Cards in this Set
- Front
- Back
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What is the principle of Snell's Law?
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That light bent when going from one medium to another.
n1(sin x1) = n2(sinx2) |
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The diopter times the focal length will always equal...
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One
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What kind of focal point do diverging lenses have?
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Negative
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What kind of focal point to converging lenses have?
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Positive
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Where is the focal point of a converging (1) diopter lens? A diverging (10) diopter lens?
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+1 meter
0.1 meters |
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What is the focal length?
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Distance between the surface (or middle) of the lens and the point of image formation.
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How is focal power calculated?
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(Refractive index)/(Focal length)
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A problem with the drainage of the aqueous humor will result in...
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Glaucome (>22 mmHg)
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Plaque formation on the lens results in...
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Cataracts
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Describe how the zonal fibers and the lens respond to ciliary muscle contraction and relaxation.
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Relaxation of CM: Zonal fibers are taut and the lens is flat.
Contraction of CM: Zonal fibers are relaxed and the lens is round. |
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How is accommodation effected by age?
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Deteriorates with age
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What is presbyopia?
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describes the condition where the eye exhibits a progressively diminished ability to focus on near objects with age
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What is myopia?
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Nearsightedness: Those with myopia see nearby objects clearly but distant objects appear blurred. With myopia, the eyeball is too long, or the cornea is too steep, so images are focused in the vitreous inside the eye rather than on the retina at the back of the eye.
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What is hyperopia?
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Farsighted: inability to focus on near objects due to a flattened cornea or short eyeball causing the focal point to be behind the eye.
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What is emmetropia?
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Normal 20/20 vision
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What lens is used to correct for myopia?
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Diverging lens
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What lens is used to correct hyperopia?
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Converging lens
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What is an astigmatism?
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Irregular curvature of the cornea or lens. Typically cornea has a football shape rather than being round.
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What is the foveola?
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Center of the fovea. Lacks capillaries.
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Where are the rods and cones located?
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Between the pigment epithelium and outer nuclear layer.
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What layer of cells form the inner layer of the eye?
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Ganglion cell layer
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What light luminance will allow the best acuity?
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2-4 luminance
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What luminance can cause damage to the eye?
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>8
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What is the absolute threshold of the eye (luminance)?
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-6
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What is the difference in rods and cones stimulation of bipolar cells?
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15-30 rods will stimulate a single rod bipolar cell, relatively slow
1 cone will stimulate a single cone bipolar cell, relatively fast |
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Describe Na, Ca, and K flow on a dark rod.
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Na influx
Ca influx K efflux Depolarized |
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Describe Na, Ca, and K flow on a light rod.
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Na: no influx
Ca: no influx K: efflux Hyperpolarized |
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Under what condition is the rod hyperpolarized or depolarized?
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dark: depolarized
light: hyperpolarized |
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A deficiency in retinal causes what pathology?
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Night blindness
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Photon absorption causes what conformational change in retinal?
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11-cis retinal to all-trans retinal
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What second messengers are involved in phototransduction?
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retinal
transducin phosphodiesterase cGMP to cause channel closure HUGE amplification |
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What is the active form of retinal?
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11 cis retinal
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How is retinal recycled after photoisomerization?
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Converted to:
all-trans retinol all-trans retinyl ester 11-cis retinol then back to 11-cis retinal |
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What two intracellular proteins in rods are mediated by Ca?
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Guanylate cyclase
Rhodopsin kinase |
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What cells are slowest in dark adaptation?
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rods (45 mins)
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How long does it take cones to dark adapt?
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10 minutes
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What is the peak absorption wavelength of rods?
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500nm
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What is protanopia?
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No red sensitivity
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What is deuteranopia?
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No green sensitivity
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When light is shone on the on-center ganglion, what happens?
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On center will fire
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How does constriction of the pupil change with depth of focus?
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increase the depth of focus
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How does dilation of the pupil change with depth of focus?
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decrease the depth of focus
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What three factors help establish depth perception?
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1. relative object size
2. parallax motion 3. stereopsis |
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What is diabetic retinopathy?
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poor blood sugar control leads to compromised vasculature in the capillaries of the eye. Causing hemorrhage.
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Parasympathetics that travel to the ciliary body will originate from which nucleus?
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Edinger Westphal
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Pupillary response afferents take the optic nerve back to the Pretectum through which other nucleus?
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The lateral geniculate nucleus
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Describe, in painful detail, the "in on II, out on III" light reflex.
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Afferent will travel on the optic nerve through the chiasm, through the geniculate nucleus, to synapse in the pretectum. It is then relayed to the Edinger-Westphal nucleus, where their is another synapse. Then the presynaptic parasympathetics will travel on III to the ciliary ganglion, where they synapse and use the short ciliary nerves to reach the ciliary body.
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Does the parasympathetic light reflex cross over in the chiasm (afferent)?
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Travels with the optic nerve. So, it will cross over where ever the optic would cross over.
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What fibers do sympathetics use to reach the eye from the superior cervical ganglion?
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V1: ophthalmic to the long ciliary
Short ciliary nerves through the ciliary ganglion |
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What area in the brain controls sympathetics?
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Hypothalamus
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Following a lesion on the visual cortex or pathways to the visual cortex, how is "Blindsight" possible?
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Via subcortical pathways to the mid-brain
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When will information from each eye mix?
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In the visual cortex
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What do Meyer's loop fibers carry? From where to where?
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Information from the inferior retinal quadrants (superior visual field).
From the geniculate nucleus to the visual cortex. |
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What anatomically separates the superior and inferior visual fields in the visual cortex?
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Calcarine fissure
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What portion of the visual field crosses over in the chiasm?
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Nasal retinal ganglion cells
Peripheral visual field |
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What is a scotoma?
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Small visual field deficit
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What is an anopsia?
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Large visual defect
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What happens if an image in unchanging on the retina?
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Disappears
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Lesions on extraocular muscles or nerves can cause what type of deficits?
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Diplopia
Strabismus |
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Describe a motor unit of the extraocular muscles.
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One neuron can activate 3 motor fibers
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What type of NT and receptors do extraocular muscles have?
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AC
Nictotinic ACh receptors |
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Which extraocular CN will only innervate muscles on the contralateral side? What muscle?
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CN IV
Superior Oblique |
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Which of the extraocular CNs carries autonomics?
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CN III
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Where will the trochlear cross over?
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Between the inferior colliculi
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With a loss of the trochlear nerve, what will the patient often do to compensate?
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Head tilt toward the weak muscle
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Where is the trochlear nucleus?
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Caudal midbrain
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Where is the abducens nucleus?
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Pons
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Which extraocular CN is most common to palsy?
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CN VI due to long course
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Where is the Oculomotor nucleus?
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mid-brain, under the superior colliculus
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What nucleus will drive the autonomics on CN III?
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Edinger Westphal
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CN III ptosis can be compensated by what other CN and muscle?
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CN VII innervation of frontalis to lift the eyebrow and eyelid
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What are the two gaze centers?
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PPRF (horizontal gaze center)
Rostral interstital nucleus (vertical gaze center) |
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What center drives horizontal saccades?
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PPRF
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How do gaze centers cross over to drive the muscle of both eyes in a saccade?
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using a medial longitudinal fasciculus (local circuit neuron)
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What centers generate saccades?
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superior colliculus in the midbrain
frontal eye field just rostral to the premotor cortex |
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What center is about to map auditory, somatic and visual information, to generate a saccade?
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superior colliculus
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Define strabismus.
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misalignment of visual axes
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Define phoria.
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latent deviation that appears only when fusion is disrupted
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Define tropia.
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manifest deviation, beyond range of fusional control
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Which direction is the eye deviated in esotropia?
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One eye is deviated towards the other
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What happens when the nonesotropic eye is covered?
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esotropic eye will gain correct fixation and the "normal" eye will become esotropic (Hering's law)
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What is understood if a nonesotropic eye becomes esotropic in a cover test, and does not return after the cover is removed? What if the eye does return to the original position?
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Both eyes have equal visual acuity and fixation.
Amblyopia is present |
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Deviation of the eye away from the other eye, but only when covered is...
What would be expected when the cover is removed? |
exophoria
Return to normal position |
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What is limited in incomitant strabismus?
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Ocular movement
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What are some diagnostic test used to evaluate strabismus?
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Cover test
Light reflex Measurement of the angle of deviation Motility testing Sensory testing (binocularity) |
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With whom is pseudoesotropia most common?
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infants
Look for normal alignment of light |
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What are the three types of restrictive strabismus?
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Congenital fibrosis syndrome
Graves disease Orbital fractures |
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What are common neurological causes of strabismus?
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CN palsy (III, IV, VI)
Myasthenia gravis |
