vision

Identify structures of the eye and explain their function

• Division of the Eyeball: 3 layer

• fibrous layer

• vascular layer

• inner layer

Fibrous Layer

• Components: Sclera and Cornea.

  • Sclera:

    • Makes up approximately 85% of the fibrous layer.

    • Provides shape and support, and attaches extraocular muscles for eye movement.

    • Visible as the white part of the eye.

  • Cornea:

    • Transparent, anterior continuation of the sclera.

    • Refracts light entering the eye.

Vascular Layer

• Components: Choroid, Ciliary Body, Iris.

  • Choroid:

    • Layer of connective tissue and blood vessels.

    • Nourishes outer layers of the retina.

  • Ciliary Body:

    • Comprised of the ciliary muscle and ciliary processes.

    • Controls lens shape via zonular fibers (suspensory ligament of the lens).

    • Ciliary Muscle:

      • Smooth muscle fibers in three orientations (longitudinal, circular, radial).

      • Contraction reduces diameter, facilitates lens accommodation for near vision.

      • Relaxation increases diameter, flattening the lens for distance vision.

  • Iris:

    • Circular structure with a central pupil aperture.

    • Eye color determined by the iris.

    • Pupil Size Control:

      • Circular Fibers (sphincter pupillae): Innervated by parasympathetic system for constriction.

      • Radial Fibers (dilator pupillae): Innervated by sympathetic system for dilation.

Inner Layer

• Components: Retina (neural and pigmented layers).

  • Neural Layer:

    • Contains photoreceptors, located posteriorly and laterally.

  • Pigmented Layer:

    • Supports the neural layer, attached to the choroid.

    • Anterior continuation forms the non-visual retina.

• Optic Part of the Retina:

  • Viewed during ophthalmoscopy or fundoscopy.

  • Macula Lutea:

    • Yellowish area containing fovea centralis (high concentration of cones for color vision).

  • Optic Disc:

    • Entry point for the optic nerve, contains no light-detecting cells (blind spot).

Fluid Areas

• Chambers of the Eye:

  • Anterior Chamber: Between cornea and iris.

  • Posterior Chamber: Behind the iris, anterior to lens.

• Aqueous Humor:

  • Nourishes and protects the eye, secreted into the posterior chamber, flows to the anterior chamber, absorbed into canal of Schlemm (scleral venous sinus).

  • Obstruction can lead to glaucoma due to increased intraocular pressure.

Vitreous Chamber

• Vitreous Humor:

  • Gel-like substance filling the eyeball, extends from behind the lens to the retina.

Identify the nerves and muscles involved in eye movement

NMONIC TO MEMORIZE THIS

• LR6 SO4 AO3

  • LR6 → Lateral Rectus (CN VI - Abducens)

  • SO4 → Superior Oblique (CN IV - Trochlear)

  • AO3 → All Others (CN III - Oculomotor) (Superior rectus, Inferior rectus, Medial rectus, Inferior oblique)

• To remember the rectus muscles, think:

  "Super Man Is Late" (SMIL)

  • Superior rectus → Moves up

  • Medial rectus → Moves in (medial/adduction)

  • Inferior rectus → Moves down

  • Lateral rectus → Moves out (lateral/abduction)

  For the oblique muscles, remember:

  "Opposites rule!"

  • Superior oblique → Moves eye down & out (depression, abduction)

  • Inferior oblique → Moves eye up & out (elevation, abduction)

Describe the autonomic innervation and musculature of the pupil

• Dilator pupillae muscle

  • Function: Dilates (widens) the pupil

  • Innervation: Sympathetic nervous system (via the superior cervical ganglion)

  • Muscle fibers: Radial fibers that pull the pupil outward

• Sphincter pupillae muscle (Constrictor pupillae)

  • Function: Constricts (narrows) the pupil

  • Innervation: Parasympathetic nervous system (via the oculomotor nerve [CN III] and ciliary ganglion)

  • Muscle fibers: Circular fibers that contract to reduce pupil size

• Parasympathetic ( rest & digest ) Pathway

  • in bright light or relaxed situations the pupils Constricts (narrows pupil)

  • it protects retina from excessive brightness to improve close up vision (accommodation)

• Sympathetic ( fight or flight ) Pathway

  • in low light or stressful situations the pupil dilates (widens pupil)

  • increasing the entry of light, which improves vision in low light and enhances awareness for potential threats

FOR FLASHCARDS

• Parasympathetic (rest & digest) → Constriction conserves energy, protects the retina, and aids in near vision.

• Sympathetic (fight or flight) → Dilation improves vision in darkness and high-alert situations, preparing for action.

Explain the role of different cell types of the retina

MNEMONIC

Rude Cats Bring Great Hugs Always, Really!"

• R → Rods (Night vision, black & white, low light)

• C → Cones (Color vision, sharp details, bright light)

• B → Bipolar cells (Bridge between photoreceptors and ganglion cells)

• G → Ganglion cells (Generate action potentials, send signals to brain, helps form optic nerve)

• H → Horizontal cells (Help with contrast and edge detection)

• A → Amacrine cells (Adjust brightness, detect motion)

• R → Retinal Pigment Epithelium (RPE) (Reduces glare, nourishes photoreceptors)

Draw and label the visual and pupillary light reflex pathways

• Steps of the Visual Pathway:

  1. Retina (Photoreceptors)

     • Rods and cones detect light and convert it into electrical signals.

     • These signals pass through bipolar cells to ganglion cells.

  2. Optic Nerve (CN II)

     • The axons of ganglion cells form the optic nerve.

     • Each optic nerve carries visual information from one eye.

  3. Optic Chiasm

     • Nasal retinal fibers (from the medial part of each eye) cross to the opposite side.

     • Temporal retinal fibers (from the lateral part of each eye) stay on the same side.

     • This crossing allows each hemisphere of the brain to process visual input from the opposite visual field.

  4. Optic Tracts

     • These continue to the brain, now carrying visual information from the opposite visual field (e.g., right optic tract carries left visual field).

  5. Lateral Geniculate Nucleus (LGN) of the Thalamus

     • The LGN relays signals to the primary visual cortex.

  6. Optic Radiations

     • Superior optic radiations (via parietal lobe) → carry signals from the inferior visual field.

     • Inferior optic radiations (Meyer's Loop) (via temporal lobe) → carry signals from the superior visual field.

Infer the location of a visual pathway lesion based on a description of visual field defects

Summary Table of Lesions & Visual Field Defects