Vision 5: Uveal Tract

Question 1

The Iris contains

Answer 1

• Pigments
• Constrictor pupillae muscle
• Dilator pupillae muscle

Question 2

Functions of the Iris

Answer 2

Prevents penetration of light waves into the eye, so light enters only through pupils

Regulation of amount of light reaching retina, by dilating or constricting Pupils:
* Constriction=1.8 mm
* dilatation=8mm

Prevents Spherical and Chromatic Abberations (blurriness or Haloes of vision:
* by Preventing lightwaves to penetrate peripheral part of the lens which has much higher curvature than central part & may act as a prism

Constriction of pupil increases Depth of focus

Protective function:
* By Light reflex, protecting against execcive light

Question 3

Structure, Nerve supply and action of Constrictor pupillae

Answer 3

• Acts as a Sphincter
• Circular in structure, around the pupil
• Supplied by Occulomotor (Parasympathetic)
• Miosis (pupil constriction)

Question 4

Structure, Nerve supply and action of Dilator pupillae

Answer 4

• Radial fibers
• T1, T2 sympathetic
• Mydrasis (pupil dilatation)

Question 5

Receptors of pupillary light reflex

Answer 5

Photoreceptors (rods and cons)

Question 6

Afferent of pupillary light reflex

Answer 6

1. Optic Nerve
2. Optic Chiasma
3. Optic tract (but no relay in Lateral geniculate body of thalamus)

Question 7

Center of pupillary light reflex

Answer 7

Pretecal Nucleus of the midbrain

Question 8

Efferent of pupillary light reflex

Answer 8

1. Pretectal Nucleus to EWN on both sides
2. EWN through Occulomotor
3. Relay in cilary ganglion
4. Post ganglionic Short cilary fibers
5. Constrictor pupillae

Question 9

Response of pupillary light reflex

Answer 9

• Direct pupillary light reflex: contraction of Constrictor pupillae & Miosis of stimulated eye
• Indriect pupillary light reflex: Miosis in non-stimulated eye

Question 10

Explain Why Miosis of non-stimulated eye occurs during pupillary light reflex

Answer 10

• Partial crossing of optic Nerve at optic chiasma
• Each pretectal Nucleus gives both EWNs

Question 10

Cause and manifestation of Argyll-Robertson pupil

Answer 10

• Cause: Neurosyphalis –> causing lesion to Pretectal Nucleus
• Manifestations: Pupil constriction occurs only during Near response (Accomodation) but fails during pupillary light reflex

Question 11

Conditions of which Pupil constriction (miosis) takes place

Answer 11

1. Near response
2. (pupillary) Light reflex
3. Sleep (parasympathetic)
4. Parasympathomemic drugs: pilocarpine
5. Morphine poisoning: Pinpointed pupil
6. Histamine
7. Horner’s Syndrome: (lesion to cervical Sympathetic)

Question 12

Conditions of which Pupil dilatation (mydrasis) takes place

Answer 12

1. Sympathetic
2. Dark Adaptation
3. Change in object depth from near to far
4. Lesion to Occulomotor (3rd CN) or EWN
5. Cocaine
6. Alcohol
7. Sympathememetic drugs: Adrenaline
8. Parasympatholytic Drugs: Atropine

Question 13

Pupil Size during Anesthesia

Answer 13

Stage 1. Normal size
Stage 2. Dilated
Stage 3. Constricted
Stage 4./ X: Dilated Again —> Death

Question 14

Desribe Chorid function

Answer 14

• Vascular
• Attachement for Radial fibers of cillary muscles
• Rich in Melanin