The Orbit and Eye - Optha W1

Learning Outcomes

• By the end of the session, students should be able to:

  • Describe the surface anatomy of the eyeball.

  • Explain the anatomy of the eye concerning layers, chambers, segments, and aqueous production.

  • Describe the vasculature of the orbit and the eye.

  • Outline the anatomy of the retina.

  • Explain the anatomy of the visual pathway.

  • Describe movements of the eye, focusing on axes, muscle action, and innervation.

  • Apply knowledge to clinical scenarios, including extraocular muscle testing, interpreting slit-lamp views, and addressing orbital trauma.

Surface Anatomy of the Eye

• **Key Structures: **

  • Inferior lacrimal papilla & punctum: Located in the lower eyelid, lined by conjunctiva.

  • Lacrimal gland: Positioned near the conjunctival fornix.

  • Conjunctival vessel: Springs from the conjunctiva covering the sclera.

  • Iris: Seen through the cornea, controlling the size of the pupil.

  • Cornea: Provides 2/3 of the eye’s refractive power and is part of the fibrous outer layer.

  • Limbus: Junction between cornea and sclera.

Anatomy of the Eye Layers

• Fibrous Layer: Outer layer comprising:

  • Sclera: Provides muscle attachment.

  • Cornea: Responsible for most of the eye's refractive power.

• Uvea (Vascular Layer): Middle layer divided into:

  • Iris: Controls the pupil's diameter.

  • Ciliary Body: Modulates lens shape and secretes aqueous humor.

  • Choroid: Supplies nourishment and facilitates gas exchange.

• Retina: Inner layer, photosensitive; composed of several parts that are critical for vision.

Segments and Chambers of the Eye

• Anterior Segment: In front of the lens; consists of:

  • Anterior Chamber: Area between cornea and iris.

  • Posterior Chamber: Between iris and lens.

• Posterior Segment: Behind the lens; contains:

  • Vitreous Body: Fills the space and helps maintain eye shape.

Circulation of Aqueous Humor

• **Aqueous Humor Production and Flow: **

  1. Ciliary Body: Smooth muscle secreting aqueous humor.

  2. Posterior Chamber: Aqueous nourishes the lens.

  3. Pupil to Anterior Chamber: Helps nourish the cornea.

  4. Scleral Venous Sinus: Aqueous humor reabsorption via the canal of Schlemm.

• Clinical Correlation: Deepening knowledge of "open-angle" and "closed-angle" glaucoma, which are associated with intraocular pressure increases.

Arterial Supply of the Eye

• Main contributors:

  • Ophthalmic Artery: Main source for the blood supply of the eye.

  • Central Artery of the Retina: Supplies the retina directly.

  • Ciliary Arteries: Provide additional circulation.

• Visual Relation: Understanding the arrangement and the significance in ocular health.

Venous Drainage of the Eye

• Includes:

  • Superior Ophthalmic Vein: Drains mainly into the cavernous sinus.

  • Inferior Ophthalmic Vein: Drains primarily into the superior ophthalmic vein.

  • Facial Vein: Anterior drainage that lacks valves, imparting potential for infection spread.

• Danger Triangle: Anatomical area from upper lip to the external nose, pivotal due to potential infections affecting the cavernous sinus.

The Retina and Fundoscopy

• Key Components of Retina:

  • Central Artery and Vein of the Retina: Key suppliers and drainers of retinal blood.

  • Fovea Centralis: Central region with the highest concentration of cones, critical for sharp vision.

  • Optic Disc: Point of CN II (optic nerve) entry and exit for blood vessels, also the blind spot due to absence of photoreceptors.

• Clinical Significance: Importance of fundoscopy for diagnosing retinal and systemic conditions, recognizing variants like ischemia affecting visual fields.

Visual Pathway

• Pathway organization ensures spatial relationships:

  • Objects in the right visual field processed by the left visual cortex and vice versa.

  • Lower visual field data processed by the upper part of the primary visual cortex.

Eye Movements and Muscles

• Axes of Eye Movement:

  • Vertical Axis: Rotation from abduction to adduction.

  • Transverse Axis: Movement from elevation to depression.

  • Anteroposterior Axis: Movements defining intorsion and extorsion.

• Extraocular Muscles:

  • Each muscle typically has a primary and potential secondary movement. Notable exceptions include the medial and lateral rectus muscles.

  • Importance of aligning gaze for more accurate clinical assessments.

Clinical Testing of Extraocular Muscles

• Methodologies to isolate muscle action during clinical testing:

  • Lateral Rectus: Abduction, innervated by CN VI (Abducens).

  • Superior Rectus: Elevates when abducted, innervated by CN III (Oculomotor).

  • Inferior Rectus: Depresses when abducted, also CN III.

  • Medial Rectus: Adducts, utilizes CN III.

  • Inferior Oblique: Elevates in adduction, innervated by CN III.

  • Superior Oblique: Depresses in adduction, innervated by CN IV (Trochlear).

Key Concepts for Review

• Comprehensive understanding of:

  • Surface anatomy and clinical implications for the eye.

  • Visual pathways relating to potential lesions.

  • Innervation and movement mechanics of extraocular muscles.

  • Retinal anatomy through the context of fundoscopy.