06.06.03 The eye: normal and abnormal
What are the stats for cataracts?
18% of Australians have a cataract requiring surgical removal NOW based on visual acuity and symptoms If you live to 100 yrs everyone will develop a cataract
What are the stats for Diabetic eye disease?
1.7 million Australians have diabetes (≈ 8% of population) Diabetic retinopathy microvascular complication of diabetes, affects one-third of people with diabetes threatens vision in 10 per cent
What affect does AMD have?
30% of Australians will develop AMD over the age of 70 10% of AMD convert to "wet" AMD requiring 4-12 weekly intravitreal injections of anti VEGF agents Results in loss of central vision Unable to read or drive
How many Australians are blind or visually impaired?
500,000
What percentage of GP consolations are related to vision?
6%
What is regarded as legally blind?
6/60
What is giant cell arteritis?
>70 An inflammatory disease of blood vessels most common true ocular emergency pale optic nerve prominent temporal artery inflammation of opthalmic artery Tx high dose steroids
What are cataracts?
A clouding of the lens inside the eye which leads to a decrease in vision. Visual loss occurs because opacification of the lens obstructs light from passing and being focused on the retina at the back of the eye. It is most commonly due to ageing. Over time, yellow-brown pigment is deposited in the lens, and this, together with disruption of the lens fibers, reduces the transmission of light and leads to visual problems. Those with cataracts often experience difficulty in appreciating colors and changes in contrast, driving, reading, recognizing faces, and coping with glare from bright lights.
What is central retinal artery occlusion?
A disease of the eye where the flow of blood through the central retinal artery is occluded. There are several different causes of this occlusion, the most common is carotid artery atherosclerosis. Giant cell arteritis is another cause.
What is glaucoma?
A group of ocular (eye) disorders that result in optic nerve damage, often associated with increased fluid pressure in the eye (intraocular pressure - IOP) Open-angle chronic glaucoma is painless, tends to develop slowly over time and often has no symptoms until the disease has progressed significantly. It is treated with either glaucoma medication to lower the pressure, or with various pressure-reducing glaucoma surgeries. Closed-angle glaucoma, however, is characterized by sudden ocular pain, redness, nausea and vomiting, and other symptoms resulting from a sudden spike in intraocular pressure, and is treated as an ocular emergency. Glaucoma can permanently damage vision in the affected eye(s), first by decreasing peripheral vision (reducing the visual field), and then potentially leading to blindness if left untreated.
How close is close enough?
A line is considered read if "more than half" of the characters are identified correctly
What is AMD?
A loss of vision in the center of the visual field (the macula) because of damage to the retina. It occurs in "dry" and "wet" forms. Macular degeneration can make it difficult or impossible to read or recognize faces, although enough peripheral vision remains to allow other activities of daily life. In the dry (nonexudative) form, cellular debris called drusen accumulates between the retina and the choroid, causing atrophy and scarring to the retina. In the wet (exudative) form, which is more severe, blood vessels grow up from the choroid behind the retina which can leak exudate and fluid and also cause hemorrhaging.
What is visual acuity?
A measure of the resolving power of the eye and refers to the spatial limit of visual discrimination Representing the smallest visual angle at which two separate objects can be discriminated
What are the stats for glaucoma?
Age 50yrs 1% Australians are affected Age 80 yrs 10% Australians are affected 50% of Australians who have glaucoma currently Do Not Know they have the condition
What are the top 4 causes of blindness?
Age related macular degeneration Glaucoma Diabetic eye disease Cataracts
Which vessels supply the eye?
Central retinal artery -> inner 2/3 of retina. 20-30% central retinal artery from the optic nerve head central retinal artery has 4 main branches in the human retina Choroidal blood vessels -> outer 1/3 of the retina. 65-85% of blood flow vital for maintenance of outer retina (particularly photoreceptors)
Which 3 thing conditions can cause acute visual loss?
Central retinal artery occlusion Giant cell arteritis Acute angle closure glaucoma
What is diabetic eye disease?
Diabetic retinopathy is the result of microvascular retinal changes. Hyperglycemia-induced intramural pericyte death and thickening of the basement membrane lead to incompetence of the vascular walls. These damages change the formation of the blood-retinal barrier and also make the retinal blood vessels become more permeable.
What is the difference between dry and wet macular degeneration?
Dry (non-neovascular) 90% of ARMD cases = slow, progressive decline in central visual function Wet (neovascular) 10% = rapid, more substantial loss of vision
What is the pathophysiology of AMD?
Dry AMD begins with characteristic yellow deposits (drusen) in the macula, between the retinal pigment epithelium and the underlying choroid. Most people with these early changes still have good vision. People with drusen may or may not develop AMD, in fact the majority of people over age 55 have drusen with no negative effects. The risk of developing symptoms is higher when the drusen are large and numerous and associated with disturbance in the pigmented cell layer under the macula. Large and soft drusen are thought to be related to elevated cholesterol deposits. Central geographic atrophy, the "dry" form of advanced AMD, results from atrophy of the retinal pigment epithelial layer below the retina, which causes vision loss through loss of photoreceptors (rods and cones) in the central part of the eye. Wet AMD Neovascular or exudative AMD causes vision loss due to abnormal blood vessel growth (choroidal neovascularization) in the choriocapillaris, through Bruch's membrane. The proliferation of abnormal blood vessels in the retina is stimulated by vascular endothelial growth factor (VEGF). Unfortunately, these new vessels are fragile, ultimately leading to blood and protein leakage below the macula. Bleeding, leaking, and scarring from these blood vessels eventually cause irreversible damage to the photoreceptors and rapid vision loss if left untreated. Only about 10% of patients suffering from macular degeneration have the wet type.
Which conditions will have RAPD?
Large retinal detachment Central retinal artery or Ischaemic central retinal vein occlusion Optic nerve ischaemia, optic neuritis, compression, asymmetric glaucoma.
Outline the pathway of the pupillary light reflex:
Melanopsin ganglion cells of the retina project bilaterally via optic tract & Sup. brachium to pretectal nuclei. Pretectal nuclei projects crossed and uncrossed fibres to the Edinger-Westphal nucleus Edinger-Westphal nucleus preganglionic parasympathetic fibres Exit midbrain with CN III and synapse with postganglionic parasympathetic neurons of the ciliary ganglion, ciliary ganglion innervates the sphincter muscle of the iris.
What are the visual field defects associated with glaucoma?
Peripheral vision first This accounts for why presentation is often quite late. Who consciously considers their peripheral vision?
What does PERLA stand for?
Pupils Equal React Light (direct and consensual) and Accomodation
What is RAPD?
Relative afferent pupillary defect Marcus Gunn pupil or relative afferent pupillary defect (RAPD) is a medical sign observed during the swinging-flashlight test
What is the ISNT rule? What is it used for?
Rim width greatest inferior > superior > nasal > temporal If not - ? glaucoma
What is the common means by which visual acuity might be measured?
Snellen chart
What is the visual field?
That portion of space in which objects are simultaneously visible to the steadily fixing eye.
Which nerves are involved in the pupillary light reflex pathway?
afferent limb II and efferent III
What is the retina?
a 10 layered structure: nerve fibre layer ganglion cell inner plexiform inner nuclear outer plexiform outer nuclea receptor layer pigmented epithelium choroid sclera
What is unique about the foveaola
avascular cones only greatest resolution
parasympathetic innervation sphincter pupillae
constricts pupil
sympathetic innervation dilator pupillae
dilates pupil
How is visual acuity measured in children?
grating acuity letter or picture matching (kay pictures, sheridan gardener, lea symbols or tumbling E)
What is show in the image?
inferior arcuate scotoma
What are the main landmarks of the retina?
macular fovea foveola
What is regarded as normal acuity?
one or two lines better than 6/6
