Y1: Term 4: Eyes
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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
Three concentric coats
- 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.
Subjective data - Health Hx
- *vision difficulty - which eye or bilateral (both)
- *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
What is a snellen chart?
chart used to test visual acuity
What's the distance for snellen chart?
Right eye is 6/18, left eye is 6/6 which eye is better?
What is presbyopia
farsightedness due to weakening of ciliary muscles and loss of elasticity in the lens.
- Round and
- Reactive to
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