Vision Flashcards by Kelsey Madden

Mammalian chromophore

Retinal

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____-retinal is transformed by light to _____-retinal

11-cis-retinal → all-trans-retinal

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Focal power is measured in?

Diopter (Dpt)

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How to calculate Dpt

Dpt = 1 / focal distance (me)

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Focal power depends on?

Lens shape
Difference between refractive indices of lens and medium
Wavelengh

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Additive colors

RGB → adds to white

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Subtractive colors

CYMK → subtracts to black

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3 transparent tissues of eye

Fovea centralis
Area centralis
Macula lutea

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Fovea centralis

Pit-like structure in central viewing area with highest concentration of photoreceptors cells

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Fovea centralis is found in what species?

Humans, monkeys and birds

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Area centralis

Flat area in central viewing area with higher concentration of photorecptor cells

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Mucla lutea

Central area of human retina where photoreceptors store yellow pigments which absorb blue lights

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Anableps

Adaptation for terrestrial and aquatic vision

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Anableps underwater vs. above water

Underwater: lens provides main refraction

Above water: cornea

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Emmetropia

Normal vision for far objects → relaxed ciliary m. flattens lens (zonular fibers under tension)

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Accomodation

Normal or compromised vision for near objects → contracted ciliary m. round lens (zonular fibers relaxed)

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Presbyopia

Stiff lens from aging → reduced accommodation

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Hyperopia

Far-sighted → bulbus is too short

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Myopia

Near-sighted → bulbus is too long

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Astigmatism

Round like football instead of baseball

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Corneal epithelium

Barrier between tear fluid and stroma

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Corneal endothelium

Barrier between stroma and aqueous humor

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Layers of corneal epithelium

Multi-layered

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Layers of corneal endothelium

Single layered

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Corneal epithelium regeneration

7 days

Corneal endothelium regeneration

Does not regenerate → stretches to maintain barrier

What is necessary to maintain transparency of stroma?

Active ion transport

Corneal epithelium is densely innervated with?

Sensory n. fibers

Swelling of the corneal _______ leads to loss of transparency and clouding of cornea

Corneal endothelium

Largest avascular organ in body

Lens

Cells in lens

Have no organelles (fiber cells)

Circulatory system in lens is driven by?

Na current generated by Na/K ATPase and followed by fluid flux

Water channels in lens which allow fluid to follow Na curent

AQP1, AQP0

Aqueous humor is secreted by?

Ciliary epithelium

Aqueous humor exists eye via?

Trabecular meshwork and Schlemm's canal

What maintains bulb inflation? And at what pressure?

Aqueous humor homeostasis as 15 mmHg

What is glaucoma?

Retinal damage due to elevated intraocular pressure

Glaucoma is commonly caused by?

Blockage of efflux pathway

What is posterior vitreous detachment?

With age the vitreous body liquefies and detaches from retina

Cones and rods are located in what layer?

Photoreceptor layer

Choroid capillary layer aka?

Tapetum lucidum

Bruch's membrane is located between?

Pigmented epithelium and choroid capillary layer

Outer limiting membrane is located between?

Outer nuclear and photoreceptor layers

Leading cause of blindness

Macular degeneration

What causes macular degeneration?

Loss of RPE (retinal pigmented epithelium) function

Functions of RPE

1. Phagocytosis of rods and cones 2. Visual circle (conversion of retinal) 3. Viamin A storage

Is all RPE pigmented?

Nope

Function of tapetum lucidum

Reflects light back into retina

Tapetum cellosum

Densely packed zinc-cysteins (dog, cat, ferret)

Tapetum fibrosum

Extracellular densely packed collagen fibers (equine, cow, sheep)

Nocturnal animals have a high density of rods/cones

Rods

2 retinal photo-pigments

1. Retinal | 2. Opsins

Opsin is an?

Apoprotein

Each photo-receptor cell expresses how many types of opsin?

Only 1

Opsins are what type of receptors?

G-protein-coupled

Opsins determine?

Spectral sensitivity

Rhodopsin is in what cell?

Rods

Opsins are in what cells?

Cones

Melanopsin is in what cell?

ipRGC (intrinsic photo-sensitive retinal ganglion cells)

Roles of melanopsin

1. Circadian rhythm 2. Alertness 3. Pupillary light reflex

Melanopsin has what effect on melatonin?

Suppresses melatonin production

Pupillary light reflex examines the integrity of?

1. Retina 2. Ipsilateral optic n. 3. Both oculomotor nn.

Mydriasis

Relaxation of iris (sympathetic n.) Atropine → mAchR antagonist

Miosis

Constriction of iris (parasympathetic) Pilocarpine → mAchR agonist

ipRG receives light and stimulates what n.?

CN II (optic)

CN II (optic) sends signal to?

Pretecta nucleus which also communicates with other side (to stimulate reflex in both eyes)

Pretecta nucleus sends signal to?

CN III (oculomotor n.)

Oculomotor n. sends signal to?

Ciliary ganglia

What innervates pupillary constrictor m.?

Ciliary ganglia

Photopic vision

In daylight → mainly cones

Scotopic vision

In night → mainly rods

Rods are ___x more sensitive than cones

100x

Purkinje effect

Wavelength shift → rods don't see red

Outer segment of rods and cones

Modified cilium with disks

Rods/cones have multiple types of photo sensors

Cones → color!

Rods/cones have low visual acuity

Rods

Depolarization leads to?

Enhanced glutamate release

Hyperpolarization leads to?

Reduced glutamate release

Guanylyl cyclase generates?

cGMP

cGMP activates?

CNGC

Cyclic-nucleotide gated cation channel Non-selective cation channel which also conducts Ca

Darkness leads to...?

Depolarization

Light leads to...?

Hyperpolarization

Light activates?

Retinal bound to rhodopsin or opsin receptor

How does light cause closure of CNGC channel?

Activated receptor activates transducin → activates PDE → breaks down cGMP

Transducin

Retina specific G-protein

Do rods and cones generate APs?

NCKX

4 Na/Ca, K exchanger

Feedback mechanism of light/dark

Cytosolic [Ca] drops when CNGC is closed due to NCKS → stimulates GC to generate cGMP

What is univariance?

Rods and cones respond to light with hyperpolarization, regarldess of wavelength

Magnitude of hyperpolarization depends on?

Spectral sensitivity of cell and intensity of light stimulus

____ cells are first cells to code light changes by changing AP frequency

Ganglion cells

OFF-ganglion has higher AP frequency leading to depolarization when?

Dark

ON-ganglion has higher AP frequency leading to depolarization when?

Light

How do rods, cones and bipolar cells code light?

Graded voltage levels and graded Nt release

ON-bipolar cell

Sign conversion Dark: hyperpolarize (when you're hyper at night you get it on) Light: depolarizes

OFF-bipolar cell

Sign conformity Dark: depolarize Light: hyperpolarize

ON and OFF ganglion cells detect?

Contrasts in luminosity

Vision Flashcards

(98 cards)