CHAPTER FIFTEEN: EYE AND VISION

Question 1

LIST THE STRUCTURES THROUGH WHICH THE LIGHT MUST PASS BEFORE IT REACHES THE VISUAL PIGMENT IN THE RODS AND CONES.

Answer 1

Air → cornea → aqueous humour → entering lens → leaving lens → vitreous humour → neural layer of retina

Question 1

DESCRIBE THE STRUCTURE AND FUNCTION OF ACCESSORY EYE STRUCTURE, LAYER OF EYEBALL, LENS, AND HUMOURS OF THE EYE. LABEL THE STRUCTURES YOU HAVE DESCRIBED ON THE EYE.

Answer 1

→ protective accessory structures
Eyebrow: shades eye from sunlight and prevents sweat from going into eye
Eyelid: protects anterior eye (blinking), tarsal glands secrete oily substance that lubricates lid
Conjunctiva: thin transparent membrane that lines lid
Lacrimal apparatus: contains lacrimal duct and gland, produces tears and drain them into nasal cavity
External eye muscles: move the eyeball

→ fibrous layer: outer layer with avascular dense connective tissue
Cornea: transparents anterior area
Sclera: opaque posterior area

→ vascular layer
Choroid: pigmented layer that nourishes eye and provides blood, also prevents scattered light
Ciliary body: extension of choroid which is a thick tissue that surrounds the lens.
Iris: pigmented layer of the eye, continuous of ciliary body

→ retinal layer
Outer pigmented layer: choroid
Inner neural layer: photoreceptors, rods, cones, bipolar neurons, ganglia, glia.

Anterior segment: aqueous humour
Posterior segment: vitreous humour

Question 2

DESCRIBE THE FUNCTIONS OF THE CILIARY BODY AND CILIARY MUSCLE. DESCRIBE THE EVENTS THAT OCCUR WHEN ADJUSTING VISION

Answer 2

Ciliary body: thick ring of tissue around the lens
Ciliary muscles: control lens shape
Ciliary processes: secrete aqueous humour
Ciliary zonules: keep lens upright, exert and don’t exert tension

Our eyes are naturally adapted to seeing farther, since ciliary muscles are relaxed, there is more tension on the ciliary zonules, making the lens flat and better able to see things from far. However to see near the ciliary muscles must contract, causing less tension on the ciliary zonules, causing the lens to bulge. The bulged lens has a higher refractive index and is able to take 2 diverged points of light and turn them into a single focal point. This process is called accommodation.

Question 3

DESCRIBE THE CAUSE, CONSEQUENCE, AND POSSIBLE TREATMENT FOR THE FOLLOWING: ASTIGMATISM, HYPEROPIA, MYOPIA, AND PRESBYOPIA.

Answer 3

→ Astigmatism: is caused by an irregular shape of the cornea, causing it to bend light strangely into the eye. This causes individuals to have blurry vision. It can be corrected with laser procedures or cylindrically ground lenses.

→ myopia: this is nearsightedness, the eyeball is too long and light entering the eye is focused in front of the retina. This can be corrected with concave lenses

→ hyperopia: this is farsightedness, the eyeball is too short and light is focused behind the retina. This can be corrected with convex lenses.

→ presbyopia: is caused by hardening of the lens as one ages, so despite the effort of the ciliary muscles the lens can accommodate light as well, thus causing farsightedness. You can wear reading glasses to correct vision.

Question 4

DESCRIBE IN DETAIL THE EVENTS OF PHOTOTRANSDUCTION, STARTING WITH LIGHT ARRIVING AT THE PHOTORECEPTOR CELLS AND ENDING WITH ACTION AT OPTIC NERVE.

Answer 4

DRAW ON IPAD

Question 5

COMPARE AND CONTRAST THE STRUCTURE AND FUNCTION OF RODS AND CONES, FIND FIVE DIFFERENCES AND SOME SIMILARITIES.

Answer 5

→ rods: non colour vision, high sensitivity, functions in dim light, low acuity, numerous, 20 rods for each cone, mostly in peripheral areas

→ cones: colour vision, low sensitivity, functions in bright light, high acuity, not as numerous, mostly in central areas.

They’re both photoreceptors that respond to light and are found in the neural area of the retina.

Question 6

DESCRIBE LIGHT AND DARK ADAPTATION AND THEIR POSSIBLE MECHANISMS

Answer 6

→ Light adaptation: when going from dark to bright light we see a glare because
Both rods and cones are strongly stimulated
Large amounts of pigments are broken down simultaneously, causing the glare
Pupils constrict
– visual acuity improves over 5-10 minutes because
Rod system turns off
Retinal sensitivity decreases
Cones and neurons rapidly adapt

→ dark adaptation: when moving from bright light to darkness we see blackness because
Cones stop functioning in low light
Bright light bleaches rod pigments, so they are turned off
Pupils dilate
– rhodopsin accumulates in the dark so, retinal sensitivity begins to increase
Transduction G protein returns to outer segments
Sensitivity increases within 20-30 minutes.