Week 3 - Fitzakerely (Vision) Flashcards by Whitney Bertram

What kind of neurotransmitters are involved in striated muscle eyelid movements?

ACh –> nicotinic

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What kind of neurotransmitters are involved in smooth muscle eyelid movements?

Norepinephrine –> alpha-1 adrenergic

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Other than spontaneous tear production, reflexive tear production, and tear production as a response to emotional stimuli, how is tear production partially regulated?

Parasympathetic Nervous System

ACh –> muscarinic

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What are the two fundamental protective mechanisms for the eye?

Blinking
Tear production

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What is the term used to describe an overflow of tears that is due to overproduction or blocked drainage?

Epiphora

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What two parts of the eye focus light on the retina?

Cornia & Lens

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What do you call an eye that is refracting normally?

Emmetropic

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Is the refractive power greater in the cornea or the lens?

Cornea

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What is accomodation?

focusing power of the lens can be adjusted to allow near vision

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What two muscles of the eyelid are striated?

Orbicularis oculi (OO)

Levator palpebrae superioris (LPS)

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What is the smooth muscle of the eyelid?

Superior tarsal muscle (ST)

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What types of muscles are activated/inactivated when they eyelid is “maintaining ocular opening”?

Tonic activation of LPS and ST

Inactivation of OO

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What types of muscles are activated/inactivated when they eyelid is performing “gentle opening/closing”?

Activation/Inactivation of LPS

Inactivation of OO

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What types of muscles are activated/inactivated when they eyelid is “adjusting to changes in globe position”?

Activation/Inactivation of LPS

Inactivation of OO

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What types of muscles are activated/inactivated when they eyelid is “blinking/firm closure of they eyes”?

OO Activation

Inhibition of LPS

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Spontaneous blinking originates in premotor brainstem structures that are highly influence by what type of activity?

Dopaminergic

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Which is faster: blink reflex or spontaneous blinking?

blink reflex

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Where are lipids secreted from in tear production?

Oil glands in the eyelids

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What kind of fluid does the lacrimal gland secrete?

Aqueous-based solution

(contains lysozyme and other enzymes that provide protection against infection)

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What does the conjunctiva secrete in tear production?

Mucous

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Does basal tear production increase or decrease with age?

Decrease

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What kind of stimulation produces epiphora?

Parasympathetic

(increase lacrimal gland activity or facilitates closure of the lacrimal duct passage)

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What system mediates epiphora due to strong emotional responses?

Limbic system (hypothalamus)

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What happens to the image as light passes through the cornea and the lens?

inverted and reversed
refracted

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Objects in the left visual field are detected by cells in what two retinal fields?

Left nasal retina & Right temporal retina

What one significant modification occurs in the topographic mag established in the retina?

Information from the nasal regions of the retinas **cross in the optic chiasm**. This ensures that info from the _left visual field_ is processed in the _right visual cortex_!

What is the refractive power of the eye in diopters?

+59 to +75D

What is the refractive power of the cornea?

+44D

In hyperopia (far-sightedness), images are focused where?

**Behind the retina**, because the axial length of the eye is less than the focal length

Hyperopia (far-sightedness) can be caused by axial hyperopia. What is this?

eyeball is too short

Hyperopia (far-sightedness) can be caused by refractive hyperopia. What is this?

refractive power of the eye is abnormall weak

How is hyerpopia (far-sightedness) corrected?

Convex lenses | (positive diopters)

In myopia (near-sightedness), images are focused where?

in front of the retina

How is myopia (near-sightedness) corrected?

Concave lenses | (negative diopters)

What is astigmatism?

curvature of the cornea or lens is not equal in all meridians, causing unequal refraction and making a portion of the image out of focus

Age, hysical trauma, radiation, or high glucose concentration in aqueous humor of diabetic patients can all cause what to happen resulting in **cataracts**?

Opacity of the lens

Blurred vision with reduced malleability causes what symptoms in presbyopia?

Decrease in the accommodative power of the lens (condition similar to hyperopia)

What shape is the lens when focusing light on the retina from a distant source?

relatively flat

What shape is the lens when focusing light from a a near source onto the retina?

stronger (rounder)

Stimulation of what causes the lens to flatten?

Sympathetic nerves (ß₂ receptors) - causes relaxation of the ciliary muscle - see distant sources

Stimulation of what causes the lens to become more rounded?

Parasympathetic ciliary ganglion neurons (via CN III, muscarininc receptors) -contraction of ciliary muscle --\> relaxes the circular fibers

What regulates the amount of light entering the eye to keep it within the dynamic range of the photoreceptors?

Iris sphinter

Myadriasis results from reflex activation of sympathetic fibers that stimulate the dilator pupillae muscles via what mechanism?

Alpha-1 receptor

The pupillary light reflex causes contraction of what muscles via muscarinic receptor activation?

Sphincter pupillae muscles

What is the afferent and efferent pathway in miosis (pupillary constriction)?

Afferent: **Optic Nerve (CN II)** Efferent: stimulation of parasympathetic fibers in **Oculomotor Nerve (CN III)** --\> contraction of the sphincter pupillae muscles

What type of glaucoma is most common?

Open angle glaucoma (slowly developing problem)

What causes open angle glaucoma?

Increase in aqueous humor production OR Blockage of outflow

The loss of vision in glaucoma is cased by what?

Compression of the: * **cornea**: edema --\> decreased transparency ("halo effect") * **retina**: damages photoreceptors * **optic nerve**: neural conduction compromised * **arterial supply**: causes necrosis

What cells secrete aqueous humor?

Ciliary epithelium

How does the sympathetic nervous system affect aqueous humor formation (inflow)?

1. Epinephrine --\> stimulate ß₂ receptors --\> increase [cAMP] --\> INCREASES FLOW 2. Norepinephrine --\> stimulate alpha-2 receptors --\> decrease [cAMP] --\> REDUCES PRODUCTION

What does ciliary epithelium secrete in order to increase aqueous humor volume via osmosis?

**Cl^-** (carbonic anhydrase --\> HCO₃^- --\> Cl^- secretion)

What are the two mechanisms of aqueous humor drainage (outflow)?

1. **Canal of Schlemm** (1°) - contraction of the sphincter pupillae 2. **Uveoscleral outflow** - reabsorption of aqueous humor through the ciliary muscle (facilitated by prostaglandins)

What two things are used to treat glaucoma by working to increase outflow?

* Cholinergic agonists * Prostaglandins

The outer layer of the retina has what primary cells?

Photoreceptors - rods & cones

The middle layer of the retina has what type of cells that receive input from the rods or cones and generate graded potentials?

Bipolar cells

The inner layer of the retina has what type of cells that generate action potentials and whose axons form the optic nerve?

Ganglion cells

What is the frequency of light perceived as when detected by photoreceptors?

Color

What is the intensity of light perceived as by photoreceptors?

brightness

Light represents what kind of energy with properties of both particles (photons) and waves?

Electromagnetic

What is the wavelength of visible light that humans can see?

350-750nm

What kind of photoreceptors can detect light as dim as 1 photon?

Dark-adapted photoreceptors (RODS)

What type of photoreceptor is responsible for scotopic vision, has a single pigment type, is more photopigment, high sensitivity, lower temporal resolution, and poor spatial resolution???

RODS!

What type of photoreceptor is responsible for photopic vision, has three pigment types, less photopigment, lower sensitivity, high temporal resolution, and good spatial resolution?

CONES!

Which type of vision/photoreceptor is better for discrimination of surfaces and movement under bright light conditions?

Photopic Vision - Cones

What are the three types of cones and their corresponding wavelengths?

Blue - short Green - medium Red - long

What does "acuity" in the visual system refer to?

The ability to discriminate fine details of the visual scene.

What clinical tool is used to assess spatial acuity?

Snellen eye charts (Low acuity = 20/200, High acuity = 20/15)

Critical fusion frequency is where a flashing light appears to be continuous rather than repetitive, which is related to what type of visual acuity?

Temporal Acuity

What type of acuity is described as the ability to distinguish differences in the wavelength of the stimuli (e.g. cone excitation in red rooms)?

Spectral Acuity

In rods, what does the activation of rhodopsin ultimately lead to?

Closure of cyclic nucleotide (cGMP) gated Na⁺ channels and hyperpolarization of the photoreceptor.

What is the resting potential of a rod photoreceptor?

about -40 mV

What is the current called that occurs in the absence of light when cGMP-dependent Na⁺ channels are open and the membrane is depolariezed?

"Dark" current

What kind of channels contained in rods tend to stabilize the membrane potential at about -70 mV?

Potassium "leak" channels | (reversal potential for K⁺ ~-70mV)

During hyperpolarization of the photoreceptor membrane, are K⁺ channels open or closed?

Still open!

What is the result of hyperpolarization of the photoreceptor membrane?

Decrease in the release of excitatory neurotransmitter

What cells gradually lose their ability to respond to light in Retinitis pigmentosa?

photoreceptors

What is the first and second symptoms of Retinitis pigmentosa?

1st = night blindness 2nd = tunnel vision

Retinopathy is a non-inflammatory damage to the retina (especially the macula), that often results from what?

Blocked blood supply

What are the first symptoms of vitamin A deficiency?

* Night blindness (due to loss of 11-cis-retinol) * dry skin/hair * broken fingernails * decreased ability to fight infections

All visual pigments consist of an opsin combined with what chromophore?

11-cis-retinal

Can 11-cis-retinal be synthesized by humans?

No! -must be converted from Vitamin A

The visual cycle consisting of the bleaching and recycling of retinoids between the photoreceptors and the retinal pigment epithelium (RPE) is present in which type of photoreceptor?

Rods (cones use Muller's cells - glia - for storage of photopigments)

Age-related macular degeneration (AMD) begins with the appearance of yellow deposits in the macula between the RPE and the choroid called what?

Drusen | (thought to be cholesterol deposits)

What happens in "dry" advanced AMD?

Atrophy of the RPE followed by loss of photoreceptors

What causes "wet" advanced AMD?

abnormal growth of blood vessels in the choroid in response to tissue damage (leads to irreversible leaking and scarring damage)

What kind of vision loss is characteristic of "wet" advanced AMD?

Loss of central vision | (expands to include the entire retina)

What is currently being used to treat macular degeneration?

anti-VEGF antibodies

Week 3 - Fitzakerely (Vision) Flashcards

(89 cards)