Term
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Definition
| Tough, outermost layer of the eye |
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Term
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Definition
| Transparent external surface, major refractive component, continuous with sclera |
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Term
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Definition
Opening that controls the amount of light
reaching the retina |
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Term
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Definition
Consists of two muscle4s, an inner circular and outer radial; pupillary diameter depends on activity of these
muscles. Eye color is based on pigmentation of iris. |
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Term
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Definition
| Fine-tunes refraction for focusing light on retina (accommodation) |
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Term
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Definition
| Sphincter-like circular muscle; controls thickness of lens during accommodation |
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Term
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Definition
| Connect lens to ciliary muscle. With relaxation of ciliary muscle, tension on these fibers is high, and lens is flat; vice versa for contraction of ciliary muscle. |
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Term
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Definition
| Highly vascularized, between retina and sclera |
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Term
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Definition
| Fluid in the anterior chamber of the eye |
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Term
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Definition
| Fluid in the posterior channel of the eye |
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Term
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Definition
| Photoreceptive area of eye |
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Term
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Definition
| Center area (1 mm2) of retina; site on retina where light falls if one looks straight ahead |
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Term
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Definition
| Center of macula, only cones are found, region of the greatest acuity |
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Term
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Definition
| Entrance of the optic nerve (blind spot) |
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Term
| What is the visible spectrum range? |
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Definition
| Wavelengths in the electromagnetic spectrum of 400 nm to 700 nm |
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Term
| What is the effect of lens refraction? |
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Definition
The image will be upside down and reversed from right to left on
the retina, 180 degrees |
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Term
| How does the eye see an object far away? |
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Definition
| Accommodation:
The ciliary muscle contracts, releasing stretch on the zonular fibers.
This allows the lens to assume a more spherical shape which increases its refractive ability. |
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Term
| What nerve contracts the ciliary muscle? |
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Definition
, innervated by the parasympathetic component of
The oculomotor nerve (preganglionic cell bodies in Edinger-Westphal nucleus) |
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Term
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Definition
| Normal vision, the lens is flat and almost all refraction is done by the cornea |
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Term
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Definition
| Far-sightedness, the eye is too short so the lens refracts to see a far away object. This makes it difficult to focus near objects. |
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Term
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Definition
| Near-sightedness, the eye is too long so far objects are focused in front of the retina and blurry |
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Term
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Definition
| With age, the lens becomes stiffer which prevents it from being able to assume a more round configuration. This reduces accommodation. |
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Term
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Definition
| This is due to an uneven curvature of the cornea, which has the effect of focusing an object at two separate places on the retina, producing blurry vision. |
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Term
| What type of contact lens would you use for hyperopia? |
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Definition
| A convex lens to increase refraction |
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Term
| What type of contact lens would you use for myopia? |
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Definition
| A concave lens to reduce refraction |
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Term
| What type of contact lens would you use for astigmatism? |
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Definition
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Term
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Definition
| A measure of the ability to distinguish two points. The greater the number of photoreceptors, and the better the eye's refractive ability, the higher the acuity. |
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Term
| How is acuity described/measured? What does 20/20 mean? |
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Definition
In terms of the visual angle, analogus to 360 degrees of a circle.
For normal 20/20 vision, you can see an object at 20' that takes up .083 degrees of space (5 minutes of arc) |
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Term
| How does a smaller pupil affect focus? |
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Definition
| A small pupil increases the depth of field of focus because, by allowing less light to reach the retina, the fuzzy edges of an object that is out of focus become darker so that the object appears to be in focus. |
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Term
| Describe the path of life through the retina |
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Definition
Light must first pass through
regions containing ganglion cells, amacrine cells, bipolar cells, horizontal cells before reaching the rods and cones
However, at the fovea the neurons in front of the photoreceptors are pushed laterally so that light has a more direct path |
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Term
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Definition
| Very sensitive to low levels of light, low acuity, contains more discs than cones |
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Term
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Definition
| Less sensitive to light, high acuity, color vision |
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Term
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Definition
Structures in photoreceptors containing a light-absorbing
molecule called retinal (a derivative of vitamin A) and opsin
At the end of the cell, there is machinery for reducing glutamate |
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Term
| List the process of phototransduction in rods |
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Definition
1. In dark, cGMP has high levels of activity and high depolarization
2. With light, retinal changes conformation
3. Opsin changes conformation
4. G-protein activated (transducin)
5. Activates cGMP phosphodiesterase
6. Low cGMP closes Na-channels
7. Cell hyperpolarizes
8. Neurotransmitter released is reduced |
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Term
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Definition
| The inflow of Na+ due to high levels of cGMP in photoreceptors in the dark |
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Term
| How do we detect different colors? |
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Definition
The different photopigments absorb light at different wavelengths, which ultimately is how we detect colors.
There are three types of cone photopigments, each of which absorbs light at a preferred wavelength |
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Term
| List the neural path from photoreceptors to the cortex |
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Definition
1. Photoreceptors
2. Bipolar cells
3. Amacrine cells /horizontal cells
4. Ganglion cells
5. Optic nerve
6. Optic chiasm
7. Optic tract
8. Lateral geniculate nucleus
9. Primary visual cortex |
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Term
| When do ganglion cells fire most actively? |
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Definition
| When the contrast between the excitatory center and the inhibitory off-center is highest |
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Term
| How is the retina divided into hemiretinas? |
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Definition
Temporal hemiretina (lateral, toward
ear) and a nasal hemiretina (medial, toward nose) |
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Term
| What hemiretinals will an object in the left visual field strike? |
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Definition
| An object in the left visual field will strike the nasal hemiretina in the left eye and the temporal hemiretina in the right eye. |
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Term
| Where are the ganglion cell axons for each hemiretinal? |
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Definition
Ganglion cell axons from the temporal hemiretina are located in the lateral half of the optic nerve
Ganglion cell axons from the nasal hemiretina are located in the medial half of the optic nerve |
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Term
| Describe the optic chiasm. What axons cross over? |
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Definition
| At the optic chiasm, all of the axons from each nasal hemiretina cross over, but the axons from each temporal hemiretina stay on the same side. This means that the left visual field will be transmitted in the right optic tract, and vice versa. |
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Term
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Definition
| The pathway where:
1. Optic tract projects retinal input to the lateral geniculate nucleus in a very specific topographical pattern.
2. The lateral geniculate neurons then send their axons to the primary visual (striate) cortex in a topographical pattern |
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Term
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Definition
| A defect in the visual field |
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Term
| What would happen to the visual field if there was transection of the left optic nerve? |
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Definition
| Loss of the left monocular zone only |
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Term
| What would happen to the visual field if there was transection of the optic chiasm? |
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Definition
| Loss of peripheral field (tunnel vision) |
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Term
| What would happen to the visual field if there was transection of the left optic tract? |
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Definition
| Loss of the entire half of the right visual field |
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Term
| Define the pupillary light reflex |
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Definition
| Bright light causes pupillary diameter to decrease (miosis). More specifically, bright light shone into one eye will cause pupillary constriction in both eyes; this reflex is therefore said to be consensual. |
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Term
| Describe the pathway of the pupillary light reflex |
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Definition
| retina → optic nerve → optic chiasm → optic tract → pretectal nucleus in dorsal midbrain → Edinger-Westphal nucleus → oculomotor nerve → ciliary ganglion → sphincter (circular) muscle of iris |
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Term
| What defects happen to the pupillary reflex if the left optic nerve is transected? |
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Definition
| No consensual response at all and no direct response in left eye |
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Term
| What defects happen to the pupillary reflex if the left oculomotor nerve is transected? |
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Definition
| No direct or consensual response in left eye, right pupil normal |
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Term
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Definition
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Term
| List the pathway of the mydriasis response |
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Definition
| Sympathetic activity → hypothalamus and midbrain → intermediolateral nucleus in upper thoracic region of spinal cord → superior cervical ganglion → radial muscle |
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Term
| Touching the cornea (or bright light/loud sounds) results in blinking. List the pathway for this response |
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Definition
| cornea → trigeminal nerve (CN V) → spinal trigeminal nucleus → facial motor nucleus (CN VII) → orbicularis oculi muscle |
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Term
| How many cranial nerves could you test if you attempted to initiate blinking with a loud noise? |
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Definition
Three:
1. Vestibulocochlear nerve
2. Trigeminal nerve
3. Facial motor nerve |
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Term
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Definition
| Production of aqueous humor is greater than drainage, resulting in increased intraocular pressure that ultimately damages the optic disk (gathering point for axons leaving the eye), thereby injuring the ganglion cell axons and producing blindness. |
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Term
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Definition
| Typically occurs in men, and typically involves a difficulty in distinguishing red and green. Due to genetic errors that result in lack or deficiency in red and green color pigments (X-linked). |
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Term
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Definition
| Clouding of the lens. Common in older individuals. |
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Term
| How is the primary visual cortex organized? |
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Definition
The major cell types described above are organized into cubes of cortex with about 2 mm of cortex per side.
Each cube is responsible for analyzing a particular point in space. Each cube has the ability to determine all of the important information (shape, motion, and color) of its territory.
Information from these cubes flows to higher order association cortex, where the information from each individual cube is combined into objects. |
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Term
| What does the dorsal pathway of the visual cortex detect? |
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Definition
| "Where" objects are, motions |
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Term
| What does the ventral pathway of the visual cortex detect? |
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Definition
| "What" objects are (identification) |
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Term
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Definition
|
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Term
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Definition
| Inability to name objects |
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Term
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Definition
| The inability to name particular faces |
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