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Ocular anatomy > Uvea iris > Flashcards

Uvea iris Flashcards

1
Q

which chamber is the iris located between

A

anterior and posterior chamber

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2
Q

which structure is the iris situtated in

A

situtated in the aqueous humour between the cornea and the lens

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3
Q

What is the centeral aperture of the iris

A

the pupil

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4
Q

What is the cause of the pigment in the iris

A

produced by the pigments in the melanocytes

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5
Q

Does blue or brown have more pigment

A

Blue has less pigment than brown, little pigment to scatter light

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6
Q

For inheritance, Is brown dominant or recessive

A

dominant, blue is recessive

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7
Q

What are two cases of issues with the pigment in the eye

A

Albinism, where the melanocytes are devoid of pigment, pink due to reflection from fundus

heterochromia iridis

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8
Q

Where does the pupillary region of the iris end

A

after the collarette

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9
Q

Description of collarette

A

located 2mm from the pupil margin

thickest portion of the iris

divides anterior surface of iris into pupillary and ciliary regions

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10
Q

Description of pupillary ruff

A

dark brown wrinkled rim of the pupil, at the pupillary margin

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11
Q

Description of Crypts of Funchs

A

Depressions in a radial pattern on the surface of the iris

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12
Q

Contraction furrow

A

Located in the outer region of the ciliary zone and becomes deeper when the pupil dilates

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13
Q

What is iris nevus

A

a dense flat area of pigment

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14
Q

What are the three layers of the iris

A

anterior border layer
stroma
pigment epithelium

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15
Q

What are the two types of cells located in the anterior border layer

A

Firboblasts and melanocytes (containts pigmented melanin)

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16
Q

Which part of the iris is the anterior borer layer absent

A

crypts of fuchs

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17
Q

What is muscles are located in the stroma of the iris

A

Smooth muscles, the sphincter and dilator

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18
Q

What is the stroma composed of

A

Highly vascular connective tissue containing collagen fibres, fibroblasts, melanocytes in a mucopolysaccharide matrix

Nerve fibres

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19
Q

Name the layers in the pigment epitherlium

A

anterior and posterior layer

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20
Q

What does pigment epithelium extend around the pupil margin as

A

It appears as pigmented pupil ruff

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21
Q

What is the anterior layer of the pigment epithelium in contact with and which muscular process is it associated with

A

The stroma of the iris and is closely associated with the muscular process of the dilator

22
Q

Where is the posterior layer of the pigment epithelium located

A

It is bathed in with aqueous humour

23
Q

What is the difference between the posterior and anterior layer of the pigment epithelium

A

Epithelial cells in posterior are larger and packed with melanin granules compared to the anterior layer which contains fewer pigment granules

24
Q

What is the posterior layer of pigmented epithelium continous with

A

continous with the non-pigmented epitherlium of the ciliary body

25
Q

Which zone is the iris sphincter muscle located

A

Located inthe pupillary zone of the iris and encircles the pupil of the iris, about 1mm wide

26
Q

What is the iris sphincter muscle surrounded by

A

blood vessels and nerves (motor and sensory)

27
Q

What does the contraction of the sphincter cause

A

pupil constriction (miosis)

28
Q

Where is the iris dilator muscle located

A

It extends from the iris root to the sphincter muscle

29
Q

What does the iris dilator muscle cause

A

pupipl dilation (mydriasis)

30
Q

what is the function of the sphincter and dilator

A

-open and close the pupil aperture

  • regulates the amount of light entering the eye

(normal adoult pupil size if often betweem 3 to 4mm in oridnary room light)

31
Q

What are the neural pathways involed in pupillary size control

A
  • afferent path, transmits neural signals towards brain
  • efferent pathway, transmits neural signals from brain
32
Q

what is direct response to light

A

Light entering one eye produces a constriction of the pupil of that eye

33
Q

What is consensual response to light

A

Pupil constriction of one eye when the light is placed on the retina of the fellow eye. Is due to partial hemidecussation of nerve fibres at the optic chiasm of the visual pathway

34
Q

What is response of the pupils brought by the afferent pathway

A

When both pupils are reactive to light stimulus directly to one eye and thus providing stimulus to the fellow eye for consensual response

35
Q

Give a description of the afferent pathway

A

retinal photoreceptors to optic nerve to hemidecussation of nerve fibres at optic chiasm to optic tract just before the LGN to pretectal nuclues to epilateral and contralateral EWN of the oculomotor nuclues

36
Q

What happens to the afferent pathway if the left eye is unable to constrict when light is shown onto it

A

In the abnormal left eye, the eye cannot send signals from the left eye to the EWN so there will be an absence of signal to cross over from the optic chaism to the opposite side of the visual system

37
Q

What is the efferent parasympathetic pathway

A

EWN exit the midbrain with the CN III (oculomotor nerve) synapse in the ciliary ganglion, parasympathetic fibres travel via short ciliary nerves to iris sphincter and ciliary body

38
Q

What is the efferent symphathetic pathway

A

Hypothalamus, synapse at ciliospinal centre of budge, synapse at superior cervical ganglion, travels with nasociliary nerve thorugh superior orbital fissure, sympathetic nerve travels via long ciliary nerve to iris dilator muscle

39
Q

Which action of the pupil is sympathetic and parasympathetic

A

Dilation is sympathetic pathway

Contraction is parasympathetic

40
Q

What will happen to pupil size with age

A

It will eventually become smaller and in advanced age, the pupil is often miotic

41
Q

What is anisocoria

A

Asymmetry in pupillary size between right and left eyes and can be either physiological and pathological

42
Q

How to tell physiological anisocoria

A

equal anisocoria in both bright and dim illumination and the asymmetry in pupil size rarely exceeds 1mm

absence of afferent pathway defect

Occurs in about 15% of population

43
Q

What does pathological anisocoria indicate

A

It indicates a defect in efferent neural pathway and pupuillary musculature

44
Q

If both eyes constrict in bright light but RE does not dilate in dim lightm what is the defective eye and the system

A

It is a right efferent sympathetic defect

45
Q

What happens to the pupil during near pupillary response

A

Constriction of pupil by iris sphincter muscle in response to change of fixation from distance to near

46
Q

Which autonomus nervous system and nerve plays a role in near pupillary response

A

Controlled by the eferent parasympathetic nervous system via the oculomotor nerve

47
Q

What is the near pupillary response

A

An accommodation-convergence-pupillary constriction reaction results from an association between the ciliary muscle medial recti muscles and iris sphicter muscle

48
Q

Why does convergence, accomodation and puppil constriction take place

A

Convergece, where medial recti muscles contracts, allows images of close object to remain on both foveas for single vission

Accommodation, where cillary muscles contraction allows image in focus on both foveas

Pupil constriction, where iris sphicter muscle contracts, which reduces spherical aberration and decreases the blur circle size which is a further optical aid to increase the depth of focus

49
Q

What is light near dissociation

A

an abnormal direct light reflex but a normal near reflex

a lesion that affects the reaction of the pupil to light yet leaves the near reaction of the pupil intact

50
Q

What is the arterial supply to the iris

A

Major arteriral circle (MAC) located in the stroma of the ciliary body which is formed from two long posterior ciliary arteries and seven anterior ciliary arteries

Ocular anatomy (15 decks)

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