EYELIDS
🔸
Normal lid movements
Lid opening:
Upper lid elevators:
the levator m. is the main elevator.
🔸
Muller m. and frontalis m. play a minor role.
🔸 Lid closure: By the orbicularis oculi m
Blinking:
-Spontaneous blinking:
• Is involuntary lid movement.
• Helps to spread the tear film evenly over the eye, and to displace the tears to the lacrimal puncta.
• Average rate: 15 blinks /minute.
• During each blink the eyes are shut for 0.3 seconds.
-Reflex blinking:
• Is a voluntary reflex to various stimuli.
• Protects the eye from the threatening stimulus.
Functions:
1. Lashes provide a mechanical screen for dust, dirt, sweat and sun light.
2. Reflex blinking protects the eyes from harmful stimuli such as approaching objects and bright light.
3- Spontaneous blinking spreads the precorneal tear film to improve lubrication of the ocular
surfaces.
4- The oily layer and part of the aqueous layer of the tear film are secreted by the lids.
Pupil
• The pupil is a black hole in the center of the iris. A- Ocular appendages Lacrimal apparatus and tear film
• The size of the pupil determines the amount of light that enters the eye.
• When being in a very bright room or in bright sunlight, the pupils become very small.
• In dimly lit rooms or at night, the pupils become larger to let as much light to enter the eye
• Tears are secreted from the lacrimal gland and through the lacrimal ducts they reach the eye
as possible. surface.
• The size of the pupil is controlled by the sphincter pupillae and dilator pupillae muscles. • When the eye blinks, it distributes tears over its anterior surface.
🔷
🔹 Light reflexes
Direct and consensual reflexes:
• In the same time as the lids close (starting from the temporal side to the nasal side) they push the
access of tears to the lacrimal puncta.
• Optic nerve fibers leave the eye to the optic chiasm and then to the optic tract. • With the help of the orbicularis muscle, a negative pressure is created inside the lacrimal sac and
• Some of the axons of optic tract enter the superior coliculous and synapse in the pretectal a pump makes the tears travel through the canaliculi to the sac.
nucleus.
• The signal is then passed to the Edinger-Wstphal nuclei of both sides.
• From the sac, tears reach the nose
• The parasympathetic outflow travels with the inferior division of the III CN into the eye via Composition of tears:
the ciliary ganglion. • Proteins
• The iris sphincter muscle responses to the signal and constricts the pupils
• Glucose
• As the signal is passed to both EW nuclei, light information given to one eye is passed on to
both pupils equally. • Minerals
• The constriction of the ipsilateral pupil to the stimulus is called direct light reflex. • Immunoglobulins
🔹
• The constriction of the contralateral pupil is called the consensual (indirect) light reflex. • Enzymes.
Near reflex:
• Upon focusing on a near object, the eyes converge, the lenses accommodate and the pupils Function of tear film:
constrict; these form the near synkinesis triad 1. Maintain an optically uniform corneal surface
2. Flush cellular debris and foreign material from the cornea and the conjunctiva.
Accommodation 3. Lubricate the corneal and conjunctival surfaces.
• The normal eye focuses images of distant objects on the retina at rest. 4. Provide nutrients to the cornea.
• To focus a near object, an increase of ocular refractive power is required. 5. Provide antibacterial protection.
This is called accommodation.
🔶Cornea
OUTER FIBEROUS LAYER
• When the ciliary muscle is relaxed, the tension on the zonules increases and the lens
moulds by the capsule into a flattened form.
• When looking at a near object, the ciliary muscle contracts and causes relaxation of • The cornea is a unique structure in the body. Although it is multilayered, it is transparent.
the zonules and the tension on the capsule is relieved; the lens attains a more spherical • Transparency is the most important physiological property of the cornea. This is due to the regular arrangement of
shape. the stromal collagen fibrils and the relative corneal dehydration in addition to being avascular.
• This results in increase in the dioptric power of the lens and allows a near object to • Corneal dehydration is maintained mainly by endothelial and epithelial pump of fluids out of the cornea.
come into focus on the fovea. • The cornea gets its metabolic needs from the vessels supplying the limbus, from the tear film and gets oxygen from the
external environment.
🔶 Duction:
🔸 Corneal wound healing:
• Epithelium: small defects regenerate from the surrounding epithelial cells, while large ones regenerate from the
- Monocular eye movement. migrating limbal stem cells.
- Consists of: • Stroma: irregular corneal fibrils and lamellae form, and lead to opacification of the corneal wound.
• Adduction: the eye turns nasally. • Descemet’s membrane: can be secreted by the nearby endothelial cells.
• Abduction: the eye turns temporally.
🔸
• Endothelium: cannot regenerate.
• Elevation: the eye looks up.
Functions of the cornea:
• Depression: the eye looks down.
• Main refractive medium of the eye (42 D).
• Intorsion: the upper pole of the eye rotates nasally.
• Part of the protective coat of the eye.
• Extortions: the upper pole of the eye rotates temporally.
🔶 Sclera
• It is tough, opaque and mainly avascular.
• It is composed of irregularly arranged collagen fibers, for this reason it is opaque.
Ocular movement
🔶
• The intraocular pressure pushing constantly outwards is contained by the sclera providing a stable viscoelastic
Version: Extraocular muscles (EOM) structure for the globe as a whole.
- Binocular eye movement.
• Each eye has 6 muscles: A- Ocular Physiology
- Four recti muscles (superior rectus, inferior rectus, medial rectus
- Both eyes move symmetrically in the same
and lateral rectus). MIDDLE VASCULARIZED LAYER
direction.
- Two oblique muscles (superior oblique and inferior oblique) OCULAR 🔶Iris
PHYSIOLOGY • It is the colored part of the eye.
• It is composed of smooth muscle fibers that adjust pupil size.
Types of ocular movements:
🔶 Vergence:
Binocular movement Both eyes move
B- Neurophysiology
related to the eye
layers of the eyeball
• It contracts and dilates to control how much light enters the eye.
• By adjusting it allows us to see under different lighting conditions
symmetrically to opposite directions:
- Convergence: both eyes turn inwards.
🔶Ciliary body
• The ciliary body is made up of:
- Divergence: both eyes turn outwards.
- The ciliary muscle which changes the shape of the lens to help focus the image on the retina.
- The ciliary processes which secrete the aqueous humor that nourishes the front of the eye.
- The zonules which support the lens.
Positions of gaze
There are 9 positions of gaze:
- The primary position of gaze: looking straight forward.
🔶The choroid:
- 4 secondary positions of gaze: dextroversion (Rt), levoversion the choroid is a layer of connective tissue and blood vessels located between the sclera (white
(Lt), elevation (up) and depression (down). of the eye) and the retina
- 4 tertiary positions: dextroelevation (Rt & up), function: providtion nourishment to surrounding eye structure
dextrodepression (Rt & down), levoelevation (Lt & up) and
the inner nural layer
🔶
levodepression (Lt & down).
The retina
The 6 cardinal directions of gaze The retina is a very thin layer of tissue that lines the inner part of the
eye. Visual cycle
Function: It receives and transmits visual input. • A visual cycle takes place in the photoreceptor layer and the RPE layer.
The retinal layers are divided into two parts: • Photopigments are present in the outer segment of photoreceptors.
- The outer RPE. • Light reaches the outer segments of photoreceptors where photopigments absorb
- The inner neurosensory retina (remaining 9 layers). light.
🔸
The retinal layers are divided into two parts:
The outer RPE.
RPE functions:
• Photoisomerization of the photopigments occur and as a result a visual signal is
created.
• Photopigments are regenerated in the RPE.
🔸
Binocular single vision and amblyopia
Most animals have two eyes; this gives a large visual field and stereoscopic depth perception
1. Providing nutrients for the photoreceptors.
2. Active transportation of metabolites, lipids and ions.
• Vitamin A is important for the formation of photopigments and for the maintenance of
health of conjunctival and corneal epithelial cells.
🔸
(binocular single vision).
Both eyes perceive a similar but slightly different image, by appreciating the disparity, a sense of depth
3. Outer blood-retinal barrier.
4. Regeneration and storage of visual pigment.
🔸
is achieved.
🔸Fusion: is blending of similar targets having minor dissimilarity present to each eye.
5. Phagocytosis of outer segment discs of photoreceptors. Physiology of vision
🔸
6. Absorption of light by the melanin - The generated electrophysiologic signals are transmitted to the ganglion cells (the
Stereopsis: integrating similar target but taken from slightly different angles. The inner neurosensory retina (remaining 9 layers): fibers of which form the optic nerve).
- Photoreceptor layer - The optic nerve fibers leave the eye and travel to the optic chiasm where the nasal
🔸
Amblyopia - External limiting membrane fibers of each optic nerve decussate.
🔸 It is reduced visual acuity in the absence of organic dysfunction in the eye or visual pathway. -Outer nuclear layer - Visual fibers leave the chiasm through the optic tracts.
The eye appears to be normal but the visual acuity is reduced despite refractive correction “lazy eye”. - Outer plexiform layer - Optic tracts terminate at the lateral geniculate body, where the optic radiations
🔸
Uniocular visual deprivation in early childhood: - Inner nuclear layer start.
🔸 Induces competition between the two eye signals at the level of visual cortex. - Inner plexiform layer - Optic radiations reach the occipital lobe and end at the occipital cortex where an
The cortex tends to follow the visual pathway of the eye with better stimulation (better vision). - Ganglion cell layer inverted image is perceived and then made erect.
🔸
Critical period
🔸 Is the period of time in which visual deprivation can cause amblyopia.
It begins at about 4 months, has maximum intensity at 6-9 months and then declines until the age of 8
- Nerve fiber layer
- Internal limiting membrane.
🔸Treatment of amblyopia should take place in the critical period, or as early as possible
years. Contents of the eyeball
• Three layers
• Crystalline lens
B- Eyeball • Three chambers:
🔸
Visual development in children
🔸 2nd week: eyes are directed to light stimuli, can not hold in this position.
- Anterior chamber
- Posterior chamber
🔸
🔸
4th week: fixation to objects ≥ 10 cm and following of bright objects.
1-3 months: foveal maturation, eye to eye contact, tracking of human faces.
3-6 months: discriminant perception of colors, recognizes and follows objects from distance of 1.2-1.8
- Vitreous chamber
by fatema okoff
🔸
meters.
🔸 6-10 months: Stereopsis and depth perception start to develop.
🔸
10-16 months: voluntary control of eye movement, perception and discrimination of light, dark, and
colors. 🔶 Crystalline lens
🔸162-4m-2 years: focusing and fixing on objects and people at different distances.
years: similar to adult’s vision.
• It is a biconvex, transparent and avascular structure.
• It is located directly behind the iris.
• It is suspended by fine ligaments (zonules).
• Its function is to focus image on the retina through the
accommodation.
🔶 Vitreous humor
• The vitreous cavity fills the space from the lens to the retina and contains vitreous
humor which is a jelly-like transparent semisolid material.
• The vitreous occupies 80% of the entire eye volume
. Functions of the vitreous:
1. Maintains internal pressure to support the eyeball and gives its form.
1. Transports nutrients to the retina.
2. Transmits light to the retina.
🔶Aqueous humor and IOP:
•Aqueous humor is the fluid contained in the eye between the lens and the cornea.
• It is a clear watery solution secreted by the ciliary processes into the posterior chamber of the eye from
where it circulates into the AC through the pupil.
• Most of the aqueous leaves the eye through the trabecular meshwork at the angle of the AC.
Functions of the aqueous:
1. Carries oxygen and nutrients into the lens and the cornea.
2. Carries waste products away from the lens and the cornea.
3. Maintains the shape of the eye through sustaining IOP higher than the atmospheric pressure.
4. Flushes away blood, macrophages and other inflammatory cells.
• The equilibrium of aqueous secretion and outflow rate is very important
. If the latter decreases it will lead to elevation of IOP.
• The average IOP is 16 mmHg (range 11-21 mmHg).
• IOP has a diurnal variation as it is higher in the morning and less at night.
🔸
Normal lid movements
Lid opening:
Upper lid elevators:
the levator m. is the main elevator.
🔸
Muller m. and frontalis m. play a minor role.
🔸 Lid closure: By the orbicularis oculi m
Blinking:
-Spontaneous blinking:
• Is involuntary lid movement.
• Helps to spread the tear film evenly over the eye, and to displace the tears to the lacrimal puncta.
• Average rate: 15 blinks /minute.
• During each blink the eyes are shut for 0.3 seconds.
-Reflex blinking:
• Is a voluntary reflex to various stimuli.
• Protects the eye from the threatening stimulus.
Functions:
1. Lashes provide a mechanical screen for dust, dirt, sweat and sun light.
2. Reflex blinking protects the eyes from harmful stimuli such as approaching objects and bright light.
3- Spontaneous blinking spreads the precorneal tear film to improve lubrication of the ocular
surfaces.
4- The oily layer and part of the aqueous layer of the tear film are secreted by the lids.
Pupil
• The pupil is a black hole in the center of the iris. A- Ocular appendages Lacrimal apparatus and tear film
• The size of the pupil determines the amount of light that enters the eye.
• When being in a very bright room or in bright sunlight, the pupils become very small.
• In dimly lit rooms or at night, the pupils become larger to let as much light to enter the eye
• Tears are secreted from the lacrimal gland and through the lacrimal ducts they reach the eye
as possible. surface.
• The size of the pupil is controlled by the sphincter pupillae and dilator pupillae muscles. • When the eye blinks, it distributes tears over its anterior surface.
🔷
🔹 Light reflexes
Direct and consensual reflexes:
• In the same time as the lids close (starting from the temporal side to the nasal side) they push the
access of tears to the lacrimal puncta.
• Optic nerve fibers leave the eye to the optic chiasm and then to the optic tract. • With the help of the orbicularis muscle, a negative pressure is created inside the lacrimal sac and
• Some of the axons of optic tract enter the superior coliculous and synapse in the pretectal a pump makes the tears travel through the canaliculi to the sac.
nucleus.
• The signal is then passed to the Edinger-Wstphal nuclei of both sides.
• From the sac, tears reach the nose
• The parasympathetic outflow travels with the inferior division of the III CN into the eye via Composition of tears:
the ciliary ganglion. • Proteins
• The iris sphincter muscle responses to the signal and constricts the pupils
• Glucose
• As the signal is passed to both EW nuclei, light information given to one eye is passed on to
both pupils equally. • Minerals
• The constriction of the ipsilateral pupil to the stimulus is called direct light reflex. • Immunoglobulins
🔹
• The constriction of the contralateral pupil is called the consensual (indirect) light reflex. • Enzymes.
Near reflex:
• Upon focusing on a near object, the eyes converge, the lenses accommodate and the pupils Function of tear film:
constrict; these form the near synkinesis triad 1. Maintain an optically uniform corneal surface
2. Flush cellular debris and foreign material from the cornea and the conjunctiva.
Accommodation 3. Lubricate the corneal and conjunctival surfaces.
• The normal eye focuses images of distant objects on the retina at rest. 4. Provide nutrients to the cornea.
• To focus a near object, an increase of ocular refractive power is required. 5. Provide antibacterial protection.
This is called accommodation.
🔶Cornea
OUTER FIBEROUS LAYER
• When the ciliary muscle is relaxed, the tension on the zonules increases and the lens
moulds by the capsule into a flattened form.
• When looking at a near object, the ciliary muscle contracts and causes relaxation of • The cornea is a unique structure in the body. Although it is multilayered, it is transparent.
the zonules and the tension on the capsule is relieved; the lens attains a more spherical • Transparency is the most important physiological property of the cornea. This is due to the regular arrangement of
shape. the stromal collagen fibrils and the relative corneal dehydration in addition to being avascular.
• This results in increase in the dioptric power of the lens and allows a near object to • Corneal dehydration is maintained mainly by endothelial and epithelial pump of fluids out of the cornea.
come into focus on the fovea. • The cornea gets its metabolic needs from the vessels supplying the limbus, from the tear film and gets oxygen from the
external environment.
🔶 Duction:
🔸 Corneal wound healing:
• Epithelium: small defects regenerate from the surrounding epithelial cells, while large ones regenerate from the
- Monocular eye movement. migrating limbal stem cells.
- Consists of: • Stroma: irregular corneal fibrils and lamellae form, and lead to opacification of the corneal wound.
• Adduction: the eye turns nasally. • Descemet’s membrane: can be secreted by the nearby endothelial cells.
• Abduction: the eye turns temporally.
🔸
• Endothelium: cannot regenerate.
• Elevation: the eye looks up.
Functions of the cornea:
• Depression: the eye looks down.
• Main refractive medium of the eye (42 D).
• Intorsion: the upper pole of the eye rotates nasally.
• Part of the protective coat of the eye.
• Extortions: the upper pole of the eye rotates temporally.
🔶 Sclera
• It is tough, opaque and mainly avascular.
• It is composed of irregularly arranged collagen fibers, for this reason it is opaque.
Ocular movement
🔶
• The intraocular pressure pushing constantly outwards is contained by the sclera providing a stable viscoelastic
Version: Extraocular muscles (EOM) structure for the globe as a whole.
- Binocular eye movement.
• Each eye has 6 muscles: A- Ocular Physiology
- Four recti muscles (superior rectus, inferior rectus, medial rectus
- Both eyes move symmetrically in the same
and lateral rectus). MIDDLE VASCULARIZED LAYER
direction.
- Two oblique muscles (superior oblique and inferior oblique) OCULAR 🔶Iris
PHYSIOLOGY • It is the colored part of the eye.
• It is composed of smooth muscle fibers that adjust pupil size.
Types of ocular movements:
🔶 Vergence:
Binocular movement Both eyes move
B- Neurophysiology
related to the eye
layers of the eyeball
• It contracts and dilates to control how much light enters the eye.
• By adjusting it allows us to see under different lighting conditions
symmetrically to opposite directions:
- Convergence: both eyes turn inwards.
🔶Ciliary body
• The ciliary body is made up of:
- Divergence: both eyes turn outwards.
- The ciliary muscle which changes the shape of the lens to help focus the image on the retina.
- The ciliary processes which secrete the aqueous humor that nourishes the front of the eye.
- The zonules which support the lens.
Positions of gaze
There are 9 positions of gaze:
- The primary position of gaze: looking straight forward.
🔶The choroid:
- 4 secondary positions of gaze: dextroversion (Rt), levoversion the choroid is a layer of connective tissue and blood vessels located between the sclera (white
(Lt), elevation (up) and depression (down). of the eye) and the retina
- 4 tertiary positions: dextroelevation (Rt & up), function: providtion nourishment to surrounding eye structure
dextrodepression (Rt & down), levoelevation (Lt & up) and
the inner nural layer
🔶
levodepression (Lt & down).
The retina
The 6 cardinal directions of gaze The retina is a very thin layer of tissue that lines the inner part of the
eye. Visual cycle
Function: It receives and transmits visual input. • A visual cycle takes place in the photoreceptor layer and the RPE layer.
The retinal layers are divided into two parts: • Photopigments are present in the outer segment of photoreceptors.
- The outer RPE. • Light reaches the outer segments of photoreceptors where photopigments absorb
- The inner neurosensory retina (remaining 9 layers). light.
🔸
The retinal layers are divided into two parts:
The outer RPE.
RPE functions:
• Photoisomerization of the photopigments occur and as a result a visual signal is
created.
• Photopigments are regenerated in the RPE.
🔸
Binocular single vision and amblyopia
Most animals have two eyes; this gives a large visual field and stereoscopic depth perception
1. Providing nutrients for the photoreceptors.
2. Active transportation of metabolites, lipids and ions.
• Vitamin A is important for the formation of photopigments and for the maintenance of
health of conjunctival and corneal epithelial cells.
🔸
(binocular single vision).
Both eyes perceive a similar but slightly different image, by appreciating the disparity, a sense of depth
3. Outer blood-retinal barrier.
4. Regeneration and storage of visual pigment.
🔸
is achieved.
🔸Fusion: is blending of similar targets having minor dissimilarity present to each eye.
5. Phagocytosis of outer segment discs of photoreceptors. Physiology of vision
🔸
6. Absorption of light by the melanin - The generated electrophysiologic signals are transmitted to the ganglion cells (the
Stereopsis: integrating similar target but taken from slightly different angles. The inner neurosensory retina (remaining 9 layers): fibers of which form the optic nerve).
- Photoreceptor layer - The optic nerve fibers leave the eye and travel to the optic chiasm where the nasal
🔸
Amblyopia - External limiting membrane fibers of each optic nerve decussate.
🔸 It is reduced visual acuity in the absence of organic dysfunction in the eye or visual pathway. -Outer nuclear layer - Visual fibers leave the chiasm through the optic tracts.
The eye appears to be normal but the visual acuity is reduced despite refractive correction “lazy eye”. - Outer plexiform layer - Optic tracts terminate at the lateral geniculate body, where the optic radiations
🔸
Uniocular visual deprivation in early childhood: - Inner nuclear layer start.
🔸 Induces competition between the two eye signals at the level of visual cortex. - Inner plexiform layer - Optic radiations reach the occipital lobe and end at the occipital cortex where an
The cortex tends to follow the visual pathway of the eye with better stimulation (better vision). - Ganglion cell layer inverted image is perceived and then made erect.
🔸
Critical period
🔸 Is the period of time in which visual deprivation can cause amblyopia.
It begins at about 4 months, has maximum intensity at 6-9 months and then declines until the age of 8
- Nerve fiber layer
- Internal limiting membrane.
🔸Treatment of amblyopia should take place in the critical period, or as early as possible
years. Contents of the eyeball
• Three layers
• Crystalline lens
B- Eyeball • Three chambers:
🔸
Visual development in children
🔸 2nd week: eyes are directed to light stimuli, can not hold in this position.
- Anterior chamber
- Posterior chamber
🔸
🔸
4th week: fixation to objects ≥ 10 cm and following of bright objects.
1-3 months: foveal maturation, eye to eye contact, tracking of human faces.
3-6 months: discriminant perception of colors, recognizes and follows objects from distance of 1.2-1.8
- Vitreous chamber
by fatema okoff
🔸
meters.
🔸 6-10 months: Stereopsis and depth perception start to develop.
🔸
10-16 months: voluntary control of eye movement, perception and discrimination of light, dark, and
colors. 🔶 Crystalline lens
🔸162-4m-2 years: focusing and fixing on objects and people at different distances.
years: similar to adult’s vision.
• It is a biconvex, transparent and avascular structure.
• It is located directly behind the iris.
• It is suspended by fine ligaments (zonules).
• Its function is to focus image on the retina through the
accommodation.
🔶 Vitreous humor
• The vitreous cavity fills the space from the lens to the retina and contains vitreous
humor which is a jelly-like transparent semisolid material.
• The vitreous occupies 80% of the entire eye volume
. Functions of the vitreous:
1. Maintains internal pressure to support the eyeball and gives its form.
1. Transports nutrients to the retina.
2. Transmits light to the retina.
🔶Aqueous humor and IOP:
•Aqueous humor is the fluid contained in the eye between the lens and the cornea.
• It is a clear watery solution secreted by the ciliary processes into the posterior chamber of the eye from
where it circulates into the AC through the pupil.
• Most of the aqueous leaves the eye through the trabecular meshwork at the angle of the AC.
Functions of the aqueous:
1. Carries oxygen and nutrients into the lens and the cornea.
2. Carries waste products away from the lens and the cornea.
3. Maintains the shape of the eye through sustaining IOP higher than the atmospheric pressure.
4. Flushes away blood, macrophages and other inflammatory cells.
• The equilibrium of aqueous secretion and outflow rate is very important
. If the latter decreases it will lead to elevation of IOP.
• The average IOP is 16 mmHg (range 11-21 mmHg).
• IOP has a diurnal variation as it is higher in the morning and less at night.
