Physiology-Case study
We will study the physiology of eyes base on case study;
1. Normal sight
2. Change the nature of object’s light.
3. Dust and water
4. Strong sun light
5. Pathogens attack
6. “Blind spot”
7. “Hollow hand”
8. Optical illusion
Physiology-Case study
Normal Sight
When we see an object, the light entering our eyes. The light then refracted when
passing through cornea and anterior cavity. Then, the light passing through the lens and
refracted again to focus onto fovea centralisi on retina. Then when reach the retina, the
photoreceptor receive the light, transduce the light energy( electromagnetic spectrum) into
nerve impulseii.
Fovea centralis
P1
Change the nature of object
1. Change the distance from actual location.
The eye need to maintain the image of object focussing on fovea centralis called
accommodation. When we put the object closer to the eye, the cilliary muscle around the
lens will be contractediii, hence the lens become thicker; increase the refraction angleiv of
light. When we put the object away from eye, the cilliary muscle will be relaxed and the
lens become thinner, decrease the refraction angle of the light.
P2
Physiology-Case study
2. Change the brighteners of object
The iris compose of 2 muscles, circular(11) and radial muscle(7). In bright light, the
circular muscle will be contracted, and the pupil become smaller. This is parasympathetic
reaction, the motor nerve from superior colliculus (9) (ocumulator nerve-10). In dim light,
the radial muscles wil be contracted, and the pupil become bigger. This is sympathetic
reaction, the motor nerve from superior cervical.
Physiology-Case study
Physiology-Case study
P3
P4
3. Change the location of object at same distance.
There are six muscles that responsible to control the location of our pupil. There are
4 rectus and 2 oblique muscle.The nerve that supply the signals are CN VI for lateral
rectus, CN IV for superior oblique and CN III for others muscles. (CN VI- Abducent
nerve, CN IV- Trochlea nerve, CN III- Oculomotor nerve ). When the object move
upwards, the oculumotor nerve supply signals to the superior rectus , and cause
contraction hence the pupil move upwards. I f the object move downwards, the
ocumulator nerve supply signals again to the inferior rectus cause contraction and the
pupil move downwards. If the object move laterally, the abducent nerve supply signals to
the lateral rectus and cause contraction and the pupil move laterally. If the object move
medially, the ocumulator nerve will supply signals to medial rectus cause contraction and
the pupil move medially. How about oblique muscles? The oblique muscles balance the
medial pull of the superior and inferior rectus, to move the pupil laterally (abduction).The
inferior oblique directs the pupil laterally and superiorly, therefore when it works
synergistically with superior rectus, pure elevation of the pupil occurs. Similarly, the
superior oblique directs the pupil inferiorly and laterally, therefore when it works
synergistically with superior rectus, pure depression of the pupil occurs. The inferior
oblique contract when receive signals from ocumulator nerve while superior oblique
Physiology-Case study
contract when receive signals from trochlea nervev. To easier remembering the nerve
supply to respective muscle; LR6,SO4,AO3 (Lateral rectus CN6, Superior Oblique
CN4,All others CN3.
P5
Physiology-Case study
P6
Dust and water
While we are playing the sand at the shore, our eyes are easily exposed to teh
sand and salty water. How can we prevent this happen? The eyebrow and eyelash
prevent the sand and water from touch the eyeball-conjunctiva mechanically. It is not
impossible for the sand and water reach the eyeball. The lacrimal gland will release
the lacrimal fluidvi-tears and slip away the dust and water. However, the changing of
npressure on cornea, cause the signals will be transmitted to the orbicularis oculi
muscle, closing the eyelid due to contraction of those musclevii.
Physiology-Case study
Strong sunlight
We are not advised to see the sun directly. Our retina have limitation to detect
the lightviii(P7). Strong uv light can damage our retina (also the x-rays and gamma
rays). Hence, when we expose to the sunlight, the retina will esnd impulse via CN2
DIRECT TO SUPERIOR COLLICULUS. Then from superior colliculus, the signal
will transmited via oculomotor nerve (parasympathetic
P7
reaction), contracting the circular muscle of iris, smaller the pupil. Otherwise,
the signals also supply to frontal nerve and cause contraction of orbicularis muscle,
cause the closing of eyelid.
i
Fovea centralis is the sharpest visual field. There are 3 factors that contribute to the sensitivity of fovea
centralis;
ii
iii
1.
Location on retina straight to the lens at posterior eyeball, at the yellow part called macula lutea.
2.
Contain of rods rather than cods. Rods is shaper receptors than cods.
3.
Shape; a pit if retina cause by displacement of neural layers, light fall down directly on pigmented
epithelium.
Caused by chemical change in molecules in pigment epithelium and photoreceptors.
When the light reach the retina, photoreceptors alerts to the changes and sends the impules to the optic
nerve, CN II. Optic nerve transmits the impulse to the virtual reflex. Then, the superior colliculus at visual
reflexes sebd the signals to the motor neurons to the cilliary muscle. This reaction is parasympathetic. But
dilation of lens (relaxation) are sympathetic reaction; the nerve will reach to virtual cortex, not virtual reflex.
Physiology-Case study
iv
Same as refractive index concepts. To reflex the light, we need 2 medium with different refractive index. At
atmosphere, the refractive index is 1.00, cornea 1.38, anterior chamber1.33 and lens 1.40. The bigger the
differentness, the higher the refraction angle.
v
The nerve named as “trochlea” as close to the trochlea ( bone structure) that hook the tendon of superior
oblique. This is to sure the direction force of superior oblique for pure elevation.
vi
Nerve that give signals for releasation of fluid is ophthalmic nerve CN5.
vii
Opthalmic nerve, CN5 also branched to frontal nerve that supply signals to orbicularis oculi muscles.
viii
The light can classified by electromagnetic spectrum. The lower the wavelength, the higher the ability to
damaging the retina.