BB2 Flashcards
define visual acuity
define intraocular pressure
Visual acuity: a measure of the ability of the eye to distinguish shapes and the details of objects at a given distance.
Intraocular pressure: how much aqueous humour enters vs leaves from the canal of Schlemm.
which nerve is the source of the lacrimal nerve?
CN V1: lacrimal nerve
- runs to lacrimal gland and gives off branches to the conjunctiva and skin of the superior eyelid, frontal nerve enters through SOF and provides sensory innervation to superior eyelid, scalp and forehead, nasociliary sensory to eyeball and has branches that serve the orbit and other parts of the face and one of its branches the ifratrochlear nerve supplies the eyelids, conjunctiva, and lacrimal sac.
what is the parasym action of CN III? [2]
- Sphincter pupillae – constricts the pupil, reducing the amount of light entering the eye.
Ciliary muscles – contracts, _causes the lens to become more spherica_l, and thus more adapted to short range vision.
what is normal physiology of the eye and aq humour?
NORMALLY: Aqueous humour flows from the ciliary processes into the posterior chamber, it then flows through the pupil of the iris into the cornea of the anterior chamber. From here the trabecular meshwork drains aqueous humour via the scleral venous sinus (Schlemm’s canal) into the scleral plexuses. Normal IOP 10-21 mmHg
what are the two types of glaucome and what are they caused by?
- Raised IOP that compresses and damages CN II
- Open angle Glaucoma flow reduced due to degeneration and obstruction of trabecular meshwork. Symptomless! (which is why its more dangerous, because it can go
- In Closed Angle Glaucoma the iridocorneal angle is completely closed. Flow of fluid inside the eye cannot pass through the canal of Schlemm. Acute symptoms !!
what are causes / risk factors of glaucoma? [4]
- Ocular hypertension
- Ethnicity, east Asian descent due to shallower anterior chamber depths
- Genetics, positive family history is a risk factor. Associated with mutations in several genes.
Extremely near or far sighted
how do u diagnose glaucoma?
- IOP via tonometry (eye is numbed via eye drops, the examiner uses a tonometer to measure the inner pressure of the eye through pressure applied by a puff of warm air or a tiny tool)
how can u treat glaucoma?
- Prostaglandin analogs increase outflow of aqueous humor through canal of Schlemm
- Beta-adrenergic receptor antagonists decrease aqueous humor production
- Alpha2-adrenergic agonists work by a dual mechanism, decreasing aqueous production and increasing outflow.
- Parasympathomimetic agonists and anticholinesterases work by contraction of the ciliary muscle, which opens the canal.
- Carbonic anhydrase inhibitors lower secretion of aqueous humor by inhibiting carbonic anhydrase in the ciliary body.
what is the pathophysiology of cataracts?
- Chemical modification of these lens proteins leads to the change in lens colour.
- Oxidative stress is thought to be a major contributor to the pathogenesis of nuclear cataracts.
- The lens normally has a low oxygen environment maintained by an oxygen gradient created by the posterior vitreous gel
- Disturbing the vitreous gel destroys this oxygen gradient and exposes the lens to higher oxygen levels.
what are signs of cataracts?
- Cataracts classically present as a gradual decrease in vision over many years that the patient may be very slow to recognise until there is some visual impairment (e.g., problems reading words on the television).
- However, under certain circumstances, such as in a patient with diabetes mellitus, there may be a relatively sudden reduction in vision.
- The change in lens proteins occurring in nuclear cataracts often causes a yellowish hue to the cataract, and patients will note a decreased richness in colours, especially blues.
- A patient with a progressing nuclear sclerotic cataract may also report inadequate glasses prescription. This may be the result of thickening of the lens, causing an increase in refractive power, and making the patient appear to be increasingly myopic (near-sighted).
- Decreased vision at night
what are risk factors for cataracts?
- Age > 65 years
- Female
- Smoking
- Long term UV exposure
- Diabetes mellitus
- Eye trauma
- Long term corticosteroid use
how do u treat cataracts?
- Stronger glasses and brighter reading lights
- Surgery to remove and replace affected lens
- There are no medicines or eye drops that have been proven to improve cataracts or stop them getting worse.
what is rombergs test and how do u test?
Romberg’s test is based on the premise that a patient requires at least two of the following three senses to maintain balance whilst standing:
Proprioception: the awareness of one’s body position in space.
Vestibular function: the ability to know one’s head position in space.
Vision: the ability to see one’s position in space.
Romberg’s test involves removing the sense of vision by asking the patient to close their eyes. As a result, if the patient has a deficit in proprioception or vestibular function they will struggle to remain standing without visual input.
what is perimetry?
Perimetry is the systematic measurement of visual field function. The two most commonly used types of perimetry are Goldmann kinetic perimetry and threshold static automated perimetry. With Goldmann or “kinetic” perimetry, a trained perimetrist moves the stimulus; stimulus brightness is held constant. The limits of the visual field are mapped to lights of different sizes and brightness.
The most commonly used one tests the central 30° of the visual field using a six degree spaced grid. This is accomplished by keeping the size and location of a target constant and varying the brightness until the dimmest target the patient can see at each of the test locations is found.
