Glaucoma & Glaucoma test Refraction Degree of cell packing in retina.

Glaucoma &

Glaucoma test

Refraction

Degree of cell packingin retina

Intrinsic Muscles of the Eye:The Iris

• Iris– circular.....constricts– radial.....…dilates

• Dilating pupil for eye exam: how to do it?

Pharmacology ofpupillary dilation:

Atropine

Intrinsic Muscles of the Eye:Ciliary Muscle

• Ciliary muscle relaxed = tension on zonular fibers = tension on lens = flattened lens = distant focus

• Ciliary muscle contracted = tension on zonular fibers reduced = less tension on lens = lens becomes more spherical =near focus

• Eye strain

Using a Microscope or Binoculars

With Convergence

1) DemonstrateConvergence

2) Measure NPA

Accommodation animation

NPA Left eye _______________mmNPA Right eye ______________ mm

Sex of subject ___ Age in months___

with corrective lenses/contacts? yes/no

Presbyopia

Disorders of Focus

• Myopia = nearsighted– eyeball too long, cornea/lens to

“strong”– image focused in front of retina– correct with concave lens

• Hyperopia = farsighted– eyeball too short, cornea/lens to

“weak”– image focused behind retina– correct with convex lens

• Astigmatism– irregular surface of lens or cornea

Cataract

•

Extraocular muscles

• Actions of extraocular muscles

• Motor innervation by CN III, IV, VI

Strabismus= misalignment of eyes

Storytime

Suprachiasmatic Nucleus for diurnal cycling

Visual reflexes:

Accomodation, Saccades,

Tracking, Pupillary reflexAka. Area 17 and V1

Evolution ofBinocular

VisionMapping the boundary of each visual field

Retinotopy

Goliath?

The Retina

• Photoreceptors– Rods– Cones

• Bipolar cells• Ganglion Cells

– axons converge at optic disk– axons constitute optic nerve

• Horizontal cells• Amacrine cells

Importance of abundantmembrane

Visual Acuity• 120,000,000 rods and

6,000,000 cones per retina

• 1,200,000 retinal ganglion cells & axons

• 105:1 convergence ratio

• Fovea: cones only, 1:1 highest visual acuity but poor sensitivity

Counting fingers andReading the Writing on the Wall

Demonstrationof

Blind Spot(diagram)

•Differences due to opsin: 4 types

Web-based color deficiency test

Trichromatic Theory of Color Vision

StargazingFinding your car in a dark parking lot

Choosing socks

Visual Purple

“Bleaching” of photopigments

The Dark Current

Phototransduction• In the DARK, rod is depolarized due to influx

of Na+ (called dark current)• In the LIGHT, rod is hyperpolarized• cGMP keeps Na+/Ca++ channels open• Light results in decrease of cGMP and thus

closure of ion channels, and• Hyperpolarization of cell, and• Reduced release of Neurotransmitter Glutamate

Properties of Retinal Ganglion Cells

• Use MacRetina software to simulate experiments of Hubel & Wiesel (1960s)

• Determine location and shape of “receptive field” of an RGC.

Properties of Cortical Neurons• Simple

– respond to stationary bar of light in certain orientation

• Complex– respond to moving

bar of light in certain orientation

• Hypercomplex– respond to moving

bar of light of a certain length in a certain orientation

Parallel Processing in the Cortex

• Motion sensitive

• Color and shape sensitive

Story of woman atstreet crossing

Why so much emphasis on the Visual System?