Y1: Term 4: Eyes

Sensory organ of vision

*Conjuctiva thin mucous membrane cover the sclera

• *Iris function is to vary the opening of its centre
• *Pupil is determined by parasympathetic and sympathic  chain of autonomic nervous system and controls the amount of light entering the retina 
• *parasympathetic branch causes constriction of the pupil
• *sympathetic branch causes dilation of the pupil

• 1. Outer fibrous sclera - tough protective white covering
• 2. Middle vascular choroid - dark pigmentation to prevent light from reflecting internally and heavily vascularized to deliver blood to retina
• 3. Inner nervous retina - inner layer retina is the visual layer of the eye light waves are changed into nerve impulses.

• * the outer layer of the eye which light passes
• *well supply with nerve endings, made up of mostly  pain fibers - tear occurs during touching & blinking.
• *vulnerable to damage ( trauma/injury) but have the ability to repair itself.
• *only transparented tissue in the body
• *obtain nutrients from the sclera by diffusion from blood vessels.
• *contribute to refraction or bending of light rays and focussing of vision
• *avascular but heavily innervated by sensory neurons

• *loss of central vision resulting in blurred vision.
• *caused by progressive degeneration of the centre of the retina
• *most common visual impairment and blindness in older adults.
• * there is no cure.

• * a group of conditions causing visual loss due to optic nerve neuropathy
• *Accompanied by an increase in intraocular pressure
• *caused by obstruction of the outflow of aqueous humor.
• *disorder can cause blindness if untreated.

• *avascular, transparent biconvex structure 
• *held in place by zonules attach to surrounding ciliary bodies
• *contraction and relaxation of muscle fibres of these ciliary bodies allows for near and far vision

*An opacity of the lens that interferes with transmission of light into the eye onto the retina

*most common cause of age related visual loss

*surgicaly corrected by implanting an intraocular lens

• *Receives visual images, partially analyses them then sends this modified information to the brain
• *two layers- outer epithelial layer and inner neural layer-contain millions of photo receptor cells

• *Begins with photoceptors cells (light dector) and cones (colour dectector) of the retina.
• *Their responses are transmitted by bipolar cells to a layer of ganglion cells
• *The axon of these gaglion cells generate an action potential which is then transmitted via optic nerve to the brain as vision

• *Newborns- eye movement is poorly coordinated, by 3-4 months fixate on single image.
• *reach adult size by 8 years old.

• Aging adults: pupil size decreases lens looses elasticity and becomes hard; harder for lens to change shape to accomodate for near vision (>40 years)
• *Cataract formation (lens opacity), glaucoma and macular deneration.

• *vision difficulty - which eye or bilateral (both)
• *Pain
• *Strabismus, diplopia (cross eye)
• *Redness/ swelling
• *watering, discharge
• *past hx of injury or surgery
• *family hx of glaucoma
• *glasses or contact lenses?

• *Snellen eye chart is used to test visual acuity.
• *Chart 6m from patient
• *pt covers one eye at a time & read lowest line
• *top no. represent distance from chart eg 6metre
• *bottom no. respresents the number next to the smallest line successfully read by pt.
• *6/6 score indicate perfect vision
• *the larger the denominator the poorer the visiual acuity

chart used to test visual acuity

6metres

Left eye

farsightedness due to weakening of ciliary muscles and loss of elasticity in the lens.

• Pupil
• Equal 
• Round and
• Reactive to 
• Light 
• Accomodation