Ophthalmology

1. Canthus of the Eye

Definition: The point where both eyelids meet.
There are two canthi of the eye:
- Medial Canthus: The inner corner of the eye, where the upper and lower eyelids meet near the nose.
- Lateral Canthus: The outer corner of the eye, where the upper and lower eyelids meet near the temples.

Table showing medial and lateral canthus of the eye with locations.

2. Eye Muscles and Nerve Control

Medial Rectus:
- Function: Responsible for adducting the eye (moving it inward).
- Weakness: Causes the eye to diverge.
- Innervation: Controlled by the Oculomotor Nerve (CN III).
- Signs:
  - Ptosis (drooping eyelid)
  - Mydriasis (dilated pupil)
Lateral Rectus:
- Function: Responsible for abducting the eye (moving it outward).
- Weakness: Causes the eye to converge and can lead to squint.
- Innervation: Controlled by the Abducens Nerve (CN VI).

Table of extraocular muscles with function, weakness, nerve supply, and signs

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3. Superior Oblique Muscle and Down Syndrome

Superior Oblique Muscle:
- Innervated by CN IV (Trochlear Nerve)
- Function: Helps with eye movement, allowing the eye to look downward and inward (important for focusing).
Down Syndrome:
- The Superior Oblique Muscle is typically not affected in Down syndrome. The condition can impact other aspects of vision, but the specific nerve and muscle control for eye movements usually remain intact.

4. Eye Findings and Their Significance

Bitot’s Spot:
- Location: Conjunctiva (white patches on the conjunctiva)
- Cause: Due to vitamin A deficiency, often seen in conditions like xerophthalmia.
Roth’s Spot:
- Location: Retina
- Cause: Associated with infective endocarditis, these are retinal hemorrhages with a white center (often caused by emboli).

Table of Bitot’s and Roth’s spots with causes and locations.

5. Conjunctivitis

1. Conjunctivitis Types and Symptoms

Type	Symptoms
Viral	– Watery discharge- Redness- Mild fever
Bacterial	– Mucopurulent discharge (thick, yellowish)- Watery discharge- High fever
Allergic	– Itching- Watery discharge

Table of viral, bacterial, and allergic conjunctivitis with symptoms

2. Night Blindness

Cause: Vitamin A deficiency
Effect: Impaired ability to see in low light or darkness due to insufficient levels of retinal (a form of vitamin A) in the eye.

3. Eyelash and Eyelid Conditions

Condition	Description
Outward (Ectropion)	Eyelid turns outward, causing the lower lid to fall away from the eye.
Inward (Entropion)	Eyelid turns inward, causing the lashes to rub against the cornea and eye.

Table of ectropion, entropion, stye, and chalazion with descriptions

4. Eyelid Pathology

Condition	Symptoms
Stye	Tenderness + Fever
Chalazion	Mild tenderness

6. Glaucoma

Cause: Increased aqueous humor production or decreased drainage.

Types:

Type	Description
Closed-Angle Glaucoma	More severe and faster progression Symptoms: blurred vision, redness, Pressure > 40 mmHg– Requires emergency care
Open-Angle Glaucoma	Iridocorneal angle does not drain properly- Drainage decreases, causing fluid retention and increased pressure

Treatment:

Medication	Action
Timolol	Beta-blocker, reduces aqueous humor production
Acetazolamide	Carbonic anhydrase inhibitor, reduces fluid production

Surgical Treatment: Iridotomy: A surgical procedure to improve drainage.

7. Cornea

Condition	Description
Keratitis (Cornea)	Inflammation of the cornea, often caused by infection or injury.
Cataract (Lens)	Opacity in the lens, leading to decreased vision.- Senile Cataract: Most common in old age.
Retinal Detachment	– Painless– Visual loss– Curtain-like shadow falling over vision.
Central Retinal Artery Occlusion	– Painless– Visual loss– Pale retina due to lack of blood supply.
Central Retinal Vein Occlusion	– Painless– Angry-looking retina due to blood congestion.

Table of keratitis, cataract, retinal detachment, CRAO, and CRVO with features.

1. Refractive Errors

Condition	Description
Myopia	Near-sightedness– Can see near objects clearly but cannot see far objects.
Hyperopia	Far-sightedness– Can see far objects clearly but cannot see near objects.
Astigmatism	Blurred vision– Can also cause double vision due to irregular curvature of the cornea or lens.
Presbyopia	Age-related condition where the ability to focus on near objects decreases with age.

Ophthalmology Made Simple For NLE NRE Step 1