Anatomy of the Eye Adnexa

Module 2

What is the Eyelids Primary Funcstion?

 help keep the eye moist, protect the eye from excessive light or injury and prevent foreign bodies from entering the eye.

What are the eye lids 4 layers

1. Skin

2. Obricularis Septum

3. Lavatory Muscle

4. Conjustiva

Where are Eyelashes located and what is the function?

Eye lashes grow in one layer on the upper and lower lids. Eyelashes serve to protect the eye even further from foreign bodies such as dust and debris. The eyelashes are ultra sensitive to touch and will cause eyelids to blink if an object gets to close.

Lacrimal Gland

Also known as the tear gland, it is located in the upper outer part of the eye socket (orbit) and continuously produces tear fluid.

Lacrimal Ducts

Small ducts that carry tears from the lacrimal gland to the surface of the eye.

Function of Tears

Tears cleanse, protect, lubricate, and moisten the surface of the eye.

Lacrimal Sac

A sac that collects tears after they drain from the surface of the eye through small canals.

Tear Drainage Pathway

Tears travel from the lacrimal gland → surface of the eye → small canals → lacrimal sac → lacrimal duct → nose.

Extraocular (Extrinsic) Muscles

Six muscles attached to the sclera that allow each eye to rotate and move in different directions.

Superior Rectus

Moves the eye upward.

Superior Oblique

Rotates the eye downward and inward, toward the nose.

Medial (Internal) Rectus

Moves the eye inward, toward the nose.

Lateral (External) Rectus

Moves the eye outward, away from the nose.

Inferior Rectus

Moves the eye downward.

Inferior Oblique

Rotates the eye upward and inward, toward the nose.

If the Extraocular Muscles aren’t working correctly what can happen?

The resulting Imbalance can make fusion difficult or even impossible, resulting in diplopia ( double vision ) very often and element in the prescription called prism will be prescribed to help alleviate this problem. 

What are the 9 Ocular Movements

• Abduction- eye moves temporally 

• Adduction- eye moves nasally 

• Depression- eye moves up 

• Intorsion- top of the eye rotates towards the nose 

• Extorsion- top of the eye rotates away from the nose 

• Convergence - both eyes move inward at the same time 

• Divergence - both eye moves outward at the same time 

• Phoria - tendency for the eye to turn from the normal position 

• Tropia - a definite deviation/ turning of the eye from the normal position

What is the Dimension of the eye

The average radius of the globe is approximately 12mm, yielding a diameter of 24mm 

Dimension of the Cornea

protrusion adding an additional 2.5mm, the axial length from front to back extends to approximately 26.5 mm. The cornea itself typically measures 12-12.5mm horizontally and 10-11mm vertically, with the central thickness of about 0.54mm that increases to around 0.67mm in the periphery. 

What is the dimension of the thinnest location of the sclera and the thickest dimension ?

The thinnest location of the sclera measures around 0.3mm, while the thickest ( around the optic nerve head) measures at 1.0mm. 

Dimension of a Pupil with bright light conditions and dark conditions

In bright light conditions ,the pupil, averages around 2-4mm and measures 4-8mm in the dark.

what is the dimension of the anterior chamber and the diameter of the optic disc?

The anterior chamber depth is approximately 3mm, while the diameter of the optic disc is roughly 1.5 - 2.2mm

What part of the camera is the Retina?

The film of the camera

What part of the camera is the the Cornea and Crystalline lens ?

The lenses, it helps focus the light

What is the refractive power of the average cornea?

43 diopters

What is the refractive power of the Crystalline Lens

20 diopters

What is the total combination of the total refractive power of the cornea and crystalline lens

60 diopters

Transparent structures of the eye

The tear layer, cornea, aqueous humor, crystalline lens, and vitreous humor are transparent structures that allow light to pass through and focus on the retina

Miracle of sight

Transparent, living eye tissues without blood vessels work together to focus about 60 diopters of power precisely onto the retina.

Index Refraction of Aqueous Humor

1.33

Index Refraction of Cornea

1.37

Index Refraction of Crystillne Lens

1.42

Index Refraction of Vitreous Humor

1.33

Cornea

The clear, window-like front part of the eye where light first enters. It is the eye’s major refractive body.

Anterior Chamber & Aqueous Humor

After passing through the cornea, light enters the anterior chamber, which contains aqueous humor. This fluid helps maintain eye pressure and nourishes the cornea.

Pupil

The round opening in the center of the iris that allows light to enter the eye. often compared with the shutter of a camera, the pupil is the black circular “hole” in the iris that regulates the amount of light entering the eye. 

Iris

The colored part of the eye that controls how much light enters the eye and reaches the crystalline lens.

Crystalline Lens

A flexible structure that changes its thickness to help focus vision at different distances.

Vitreous Humor

A gel-like substance that light passes through and that helps maintain the shape of the eye.

Retina & Optic Nerve

The retina acts like the eye’s “film,” converting light energy into electrical impulses. These impulses travel through the optic nerve to the brain, where they are processed into sight.

Rods

Photosensitive receptors in the retina responsible for night vision, peripheral vision, and seeing in black and white.

Cones

Photosensitive receptors in the retina responsible for day vision, detail, and color vision.

Macula

A small, sensitive area in the center of the retina that provides central vision needed for fine detail and reading.

Fovea Centralis

A small depression in the center of the macula that contains only cones, not rods, and provides the sharpest or most acute vision.

Photosensitive Receptors

Specialized cells in the retina, including rods and cones, that respond to light and help create vision.

What are the Non-Transparent structures of the eye

1.Choid

2. Sclera

3. Iris

4. Optic Nerve

Defniton of Choid

a blood rich layer underneath the retina that functions to provide nutrients to the retina as well as to the other parts of the eye. 

Definition of Sclera

is the tough, leather like outer coating of the eye, also known as the “white” of the eye. It provides protection and helps maintain the eye shape. The sclera joins and is continuous with the cornea.

Chambers of the Eye

The eye is divided into three main spaces or chambers: the anterior chamber, posterior chamber, and vitreous chamber.

Anterior Chamber

The space between the back of the cornea and the front of the iris.

Posterior Chamber

The space between the iris and the lens.

Vitreous Chamber

The largest space in the eye, located between the lens and the retina.

Accommodation

The process by which the eye adjusts to view objects at different distances by changing the shape of the crystalline lens through the action of the ciliary muscle.

Ciliary Muscle

A muscle that helps the crystalline lens change shape during accommodation to focus on objects at different distances.

Convergence & Pupil Constriction

During accommodation, the eyes may turn inward (convergence) and the pupils constrict to help focus on nearby objects.

Accommodation for Near Vision

The exact monocular near PD’s can be measured with a pupilometer

Calculating Pupillary Distance Less than 62mm

Subtract 1.5mm

Calculating Pupillary Distance 62-66mm

Subtract 3 mm

Calculating Pupillary Distance more than 66 mm

subtract 4 mm