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Ocular Anatomy

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Outline to go wtih the PECAA video

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  • Ocular Adenexa

    • Orbital Bones​

      • There are 7 bones that form the orbit. Maxilla, Frontal, Zygomatic, Ethmoid, Lacrimal, Palatine, and Sphenoid​

    • Extra-Ocular Muscles (EOMs)

      • There are 6 EOMs that control eye movement. ​

      •      Muscle               Primary Action  Secondary Action     Tertiary Action

      • Lateral Rectus            Abduction                  --                           --

      • Medial Rectrus           Adduction                  --                           --

      • Superior Rectus          Elevation             Intorsion               Adduction

      • Inferior Rectus           Depression           Extorsion               Aduction

      • Superior Oblique         Intorsion            Depression             Abduction

      • Inferior Oblique           Extorsion              Elevation             Abduction

    • Lacrimal System​​

      • Produces both our basal tears (normal tear secretion) and reflex tears (tears due to irritation and emotions). ​

      • The lacrimal gland produces the bulk of our tears. 

    • The Tear Film

      • The tear film has three layers. ​

      • ​The Lipid Layer is produced by the Meibomian Glands. ​

      • The Aqueous Layer is produced by the Lacrimal Gland. 

      • The Mucous Layer is produced by the Goblet cells of the conjunctiva. 

      • The tears are drained through the punctum to the canaliculi to the lacrimal sac out the nasolacrimal duct. 

    • Eyelids

      • The eyelids function to protect the eyes from foreign bodies and to spread our tears. ​

      • The canthus is the corners of our eyes. The caruncle is the fleshy mound in the inside corners of our eyes. The plica semilunaris is located here as well.

      • The meibomian glands are located inside the eyelids.

      • The orbicularis muscle closes the eye. This is innervated by the 7th cranial nerve. 

      • The levator muscle opens the eye. This is innervated by the 3rd cranial nerve. 

    • Conjunctiva

      • The palpebral conjunctiva covers the inner eyelids. The bulbar cnjunctiva covers the front portion of the eye. The fornix is where the two meet. ​

    • Sclera

      • This covers roughly 5/6 of the eye, providing protection. ​

    • Anterior Segment

      • This is the entire part of the eye that is seen with the slit lamp. ​

      • It includes the cornea, iris, ciliary body, and crystalline lens. 

    • Cornea

      • This is a convex plus powered lens located on the anterior 2/3 of the eye. ​

      • It is transparent, meaning that there are no blood vessels here. 

      • It derives its oxygen from the tears and the aqueous humor. 

      • There are plenty of nerves here, meaning that it is sensitive. 

      • There are five layers, measuring roughly 1mm in the periphery and 0.5mm centrally. 

        • Epithelium- Damage here would not lead to scarring. ​

        • Bowman's Membrane

        • Stroma- This represents 90% of the cornea. It contains water and keratocytes. 

        • Descemet's Membrane- This is a basement membrane of the endothelium. 

        • Endothelium

      • Limbus- This is where the cornea meets the conjunctiva. 

    • Iris

      • This contains the dilator muscle that opens the iris and the sphincter muscle that closes the iris. ​

      • All patients have different colored irises, which make us all unique. 

    • Pupil

      • Dilation vs. Non-dilation​

    • Angle

    • Ciliary Body

      • This contains the ciliary processes that produce the aqueous humor and the ciliary muscles that help us accommodate. ​

    • Aqueous Humor

      • The aqueous is produced in the ciliary processes and then travels to Schlemm's canal and then to the trabecular meshwork. Blockage here can increase the IOP. ​

    • Crystalline Lens

      • This is comprised of an outer capsule, a cortex, and then an inner nucleus. ​

      • Zonules are attached from the lens to the ciliary muscle. 

      • It's function is to help us focus light onto the retina, or accommodate. 

        • Contraction of the lens makes is more convex, and focuses light more at near. ​

        • Relaxation of the lens makes it more flat, which gives us better distance visual acuity. 

        • This focusing power decreases with age due to the inelasticity of the ciliary muscle and the hardening of the lens. 

        • This starts worsening at about 45 years of age, leading to presbyopia, and the need for reading glasses. 

    • Posterior Segment

      • This is the part of the eye seen with ophthalmoscopy, which includes the vitreous, retina, choroid, and optic nerve. It is the posterior 2/3 of the eye. ​

      • Both the OCT and Optomap can be used to view the anatomy here. 

    • Choroid

      • This layer is continuous with the iris and ciliary body. ​

      • It functions to nourish the eye. 

    • Vitreous

      • It's function is to maintain the shape of the eye and act as a shock absorber. ​

    • Retina

      • This layer of the eye houses the sensory receptors (photoreceptors), including the rods for night vision and peripheral vision, and the cones for central vision and color vision. ​

      • The macula is the area of the retina where there is an increased number of cones. The peripheral retina has an increased number of rods. 

      • With fundus photography, pictures of the optic disc, macula, and fovea will be taken. 

      • The optic disc is the area of our blindspot, since there are no rods or cones here. 

    • Visual Pathway

      • An image travels from the optic nerve to the chiasm, to the optic tract, to the lateral geniculate body, to the optic radiations, to the cortical center of the brain. ​

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Test Your Knowledge

1. The ocular adenxa

     a. is located inside the eye 

     b. is the anterior chamber of the eye

     c. surrounds the eye

     d. does not exist

2. Maxilla, Zygomatic, and Frontal are

     a. extraocular muscles

     b. orbital bones

     c. parts of the lacrimal system

     d. none of the above

3. Lipid layer, aqueous, and mucus layer are

     a. parts of the tear film

     b. extraocular muscles

     c. orbital bones

     d. none of the above

4. The eye tearing as a result of a foreign body is called

     a. reflex tears

     b. basal tears

     c. either a or b

5. How many bones are in the orbit? 

     a. 3

     b. 5

     c. 6

     d. 7

6. The cornea is approximately ___mm thick in the center. 

     a. 1

     b. 0.5

     c. 1.5

     d. 2

7.  The cornea is approximately ___mm thick in the periphery. 

     a. 1

     b. 0.5

     c. 1.5

     d. 2

8. The cornea, pupil, and lens are located in the 

     a. anterior segment

     b. posterior segment

9. This functons as a shock absorber and maintains the shape of the eyeball

     a. aqueous humor

     b. vitreous humor

10. This is located in the center of the macula

     a. fovea

     b. optic disc

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