D2 Medical Information Flashcards
Extraocular Muscles
6 extraocular muscles
4x on cardinal points behind eye…superior rectus, medial rectus, inferior rectus, lateral rectus. eye to moves toward the contracting muscle
1x superior oblique originates at the posterior orbit, near the origin of the four rectus muscles. Rotates eye medially (internally)
1x inferior oblique muscle originates from the floor of the orbit. When it contracts, it laterally rotates the eye, in opposition to the superior oblique.
Orbit
Protect / Position eye
7 bones, ocular muscles attached, optic nerve passes through back
Fat in the orbit cushions the globe = protection of socket
4 muscle start from around the apex of orbit, 2 muscle starts on temporal and nasal side of orbit
Conjunctiva
Mucus membrane covering the outer surface of the eyeball and inner surface of the lid.
Provides protection and helps keep foreign bodies out of the eye.
Lubricates with a clear viscous fluid and produces tears and mucus to act as a barrier.
Sclera
white outer layer from cornea in front of the eye to optic nerve at the back.
muscles attach to the sclera
gives structure and strength
protects
Cornea
clear cover over the iris, pupil and anterior chamber
converges light rays to start the job of focusing
Most refractive power (light bending power)
Iris
Coloured disk between cornea and lens
Controls light entering eye
Extension of ciliary body
Creates the pupil / controls size of pupil
Ciliary Body / Muscle
Connected to iris to adjust light coming in
Zonule fibres connect ciliary body and lens (suspended
Zonule fibres relax or tense lens for near/far focus
Eye Chambers
3 chambers in eye:
anterior chamber is the space between your cornea and iris,
posterior chamber is the space between your iris and the lens of your eye
vitreous chamber is the large chamber at the back of your eye
Aqueous humor
transparent liquid in anterior and posterior chamber… 99.9% water, the other 0.1% consists of sugars, vitamins, proteins and other nutrients
Secreted from the ciliary body
Both the anterior and posterior chambers are filled with aqueous humour
nourishing the cornea and the lens by supplying nutrition such as amino acids and glucose, maintain intraocular pressure
continuously produced by the ciliary body and drained (if not it will contribute to raised intraocular pressure and glaucoma)
critical to the eye’s shape and size, and the quality of image it produces
Vitreous humor
The vitreous humor (also known as vitreous fluid) is a transparent, colourless, gel-like substance that fills vitreous chamber (between lens and retina)
Helps regulate eye pressure and shape
Choroid
Layer of blood cells (or vascular layer) that provides blood and nourishment the retina
Forms part of uvea (with ciliary body and iris)
Lies between retina and sclera and extends from the optic nerve around to the ciliary body
Fovea
Small central pit at centre of macula
Only has cones
Macula
5mm oval yellowish area area surrounding the fovea near centre of retina
Cornea and lens focus light there
Provides visual acuity to read, recognise faces and most important images created and send to brain via optic nerve
Very high concentration of photoreceptor cells
Needs to be undisturbed and dry for clear vision
Diabetic retinopathy and AMD target here
Retina
Light sensitive nerve tissue forming inner layer at posterior of globe held in place largely by intraocular pressure
Rod photoreceptors cells: greater number than cones mainly on periphery (edges) of retina, allows you to see what is above, below and to sides of object you are directly viewing, work in low light. Works better than cones in low light,
Cone photoreceptor cells: concentrated in macula, fine detail / colour vision, reading / people’s faces, works well in good light
Converts images from optic system to electric impulses sent along optic nerve to brain
Like camera film
Lens
Transparent structure that refracts light
Adjusts by ciliary muscle contract / relax
Located in posterior chamber
Pupil
A hole … adjustable opening in centre of eye
Controls the amount of light entering eye by iris getting bigger or smaller
Fundus
Inside, back surface of the eye (made up of retina, macula, optic disc, fovea and blood vessels)
Fundus photography = camera points through the pupil to the back of the eye and takes red / orange picture to help find, watch and treat disease
The fovea is a small depression within the neuro, sensory retina where visual acuity is the highest . It’s the central part of the macula.
Visual Pathway
Carries neural impulses from retina to occipital lobe in brain
Blind spot as there are no cones or rods at the optic disk
Electric Impulse travels…
Retina
Optic disk
Optic nerve (single eye information)
Optic chiasm (split of nasal and temporal from single eye)
Optic tract
Lateral geniculate body (LGN) = relay centre split info into…
Optic radiations … Meyer’s loop (superior portion of visual field), central bundle, dorsal bundle
Visual cortex
Higher-order visual pathway for processing:
Dorsal Stream WHERE IS IT? (‘vision for action’ or the ‘where’ pathway - helps us size up visual scene)
Temporal Stream WHAT IS IT? (‘vision for identification’ to recognise objects, patterns, textures and shapes… choose a pear in bowl of fruit, pick circle block in line of squares, distinguish puppy and cat
Cerebrum
Top part of brain
Receives and gives meaning to information from sense organs and controls the body
Essential for memory, reasoning, communication, emotions, plus..
2 hemispheres and contains the major lobes of the brain
Cerebellum and brainstem sit below cerebrum and work to control voluntary actions in the body
Control centre for sensory processing, emotional control, motor control, personality, learning, problem solving, language and speech, visual information, cognition and higher thought, imagination, creativity, music interpretation.
Receives and interprets much of physical world
Brain Stem
Breathing
Body temperature
Digestion
Alertness / sleep
Swallowing
Cerebellum
Below Occipital Lobe, near brain stem
Balance, coordination and control of voluntary movement
Fine muscle control
Cerebral cortex
Outer most layer of cerebrum (aka gray matter - uneven surface with many folds called sulci help increase surface area of cerebral cortex
Houses four major lobes… frontal, parietal, occipital, temporal
Each lobe has 2 sections divided by central fissure
Frontal Lobe
Above temporal lobe and in front parietal lobe
Back of FL holds primary motor cortex - controls and process most voluntary movement
Regulate reward and motivation (dopamine sensitive neurons for pleasure, attention, planning and memory)
Predict consequences of actions
Impulse control (damage = difficulty with addiction, aggressive behaviour, socially inappropriate choices)
Regulate (selective) attention (damage = difficulties with planning, ADHD symptoms, executive function issues)
Right = Problem solving, planning, attention, names, judgement, analysing,
Left = Emotional Traits, ideas, art, social, creativity, music, imagination
Parietal Lobe
Above occipital and behind frontal lobe
Sensory perception and integration
Spatial reasoning and sense of your body’s movement within the world
Without parietal lobe you would still take in sensory information from eyes, ears, and other senses but you might not be able to understand the information or assign meaning to it.
Discriminate objects via touch
Understand numbers and relationship between them
Spatial reasoning, understanding, mapping
Coordinate eye, arm, hand motions
Language processing (damage = difficulty speaking or understanding language)
Handles most sensation / senses… proprioception, touch, temperature, pain, taste
Also helps with mapping and organisation of visual scene, reading, body orientation, knowing left and right.
Temporal Lobes
Located just beneath temples, parietal lobe and occipital (forms under side of cerebrum).
Processing conscious memories
Forming and processing and storing visual memories
Assigning meaning to visual inputs and memories (What?)
Producing speech (damage = difficulty understanding language)
Recongising language
Regulating unconscious emotional processes such as hunger and thirst
Maintaining homeostasis (stable body temp/heart rate)
Right = sounds, shapes and colours
Left = language and words, speech
Occipital Lobes
Interpreting visual information around the body like distance, depth, shape, colour, location of object (damage = irregular vision, difficulty standing, blindness, also epilepsy link)
4 sections:
Primary visual cortex (V1) - receives info from retina, interprets and transmits info related to space, location, motion, colour through 2 steams (D&V)
Secondary visual cortex (V2) - receives info from primary, deals much the same as V1
Dorsal stream - WHERE/HOW shares info about object location and carries it to parietal lobe which take other info about space and shape of objects
Ventral stream (V2) - WHAT takes information to temporal lobe which interprets and helps give meaning to objects in field of vision
In posterior region of cerebral cortex (furthest back in brain)
Data management system responsible for vision and colour perception
Low Vision Mobility Challenges
Light Management… Glare, Light Adaption, Low Light
Terrain Changes
Judging speed/distance
Fluctuating
Nystagmus
GENERAL:
Repetitive, involuntary movement: up and down, circular, side to side
Idiopathic but often symptom of another eye problem (e.g. albinism, neurological problem, refractive error, etc)
ISSUES:
Blurry, shaky VA (but will not appear so to congenital)
Depth perception (stereo vision degraded)
Balance and dizziness
Vertigo
STRATEGIES
Null point
Large Print
Magnification
Increased lighting
Strabismus & Amblyopia
GENERAL: not completely understood but something to do with eye muscles and nerves. Associated with stroke, trauma, infections,
Strabismus – lazy, turned, crossed eye (can lead to amblyopia). Problem with eye muscle control, brain receives 2 different images and may learn to suppress image from weaker eye.
Esotropia – inward turning
Exotropia – outward turning
Hypertropia – upward turning
Hypotropia – downward turning
Amblyopia – failure of one or both eyes to achieve VA despite normal structural health of eye. Brain begins to ignore a weaker eye (can cause strabismus).
ISSUES:
Depth perception
Double vision
Visual Acuity
Fatigue
Headaches
Clumsiness, poor hand-eye coordination
STRATEGIES… Strabismus usually fixed when found and treated early
Alignment and focus test
Prescription glasses/contact lenses help eyes focus on objects with less effort and improve ability to remain aligned
Patching stronger eye and Eye Exercises for weaker eye classic treatment to build up weaker eye
Medications botox weaken overactive eye muscle
Surgery for severe cases manipulate length and position of muscles in and round eyes.
Myopia
GENERAL
Nearsighted / shortsighted, cornea or lens has too much curvature for length of eyeball, light focuses in front retina, treated with concave lens.
The eyeball is elongated and a little bit squished down
Increasing rapidly throughout the developed world, suggesting environmental factors are involved
ISSUES
VA far object blurry
Headaches
Sitting close to TV, screen
Excessive blinking / eye rubbing
Unaware distant objects
STRATEGIES
Prescription glasses, contact lenses, refractive surgery
Neurological Vision Impairment
GENERAL
Electric Impulse: Retina, Optic nerve, Optic chiasm, Optic tract, Lateral geniculate body, Optic radiation, Visual cortex
Lesion before Optic chiasm = total right eye visual loss
Lesion at centre X Optic chiasm = nasal information gone from each eye (field loss on outside OR bitemporal (heteronymous) hemianopia)
Lesion on side Optic chiasm = temporal information gone from L eye = L nasal hemianopia
Lesson on optic tract = homonymous hemianopia
Lesion at Optic radiation = superior or inerior quadrantanopia (if on line line cut) or homonymous hemianopia with macular sparing (if all lines cut near the visual cortex)
L eye (Nasal Hemifield) and R eye (Temporal Hemifield) travels down RHS but represents left side of image
Right-sided homonymous hemianopia, which results after left-sided surgeries, can have a severe impact on learning to read in children who read languages that are written and read from left to right. skilled readers take in words from a small area around the eyes’ fixation point – about four letters to the left and 15 letters to the right. The more letters you can see on the right, the faster your reading speed because you know which word to focus your eyes on next. Adult readers with left-sided brain injury resulting in right-sided hemianopia describe severe frustration when reading because they are attempting to read into nothingness.
ISSUES
Unaware of field loss, don’t see visual field loss. The child lacks vision in the lost visual field in the same way that you lack vision behind you. You do not see black behind you, but instead see nothing
bump into pedestrians or obstacles that they simply cannot see because the object or person is in the lost field of vision
trouble with activities which require good vision, like team sport activities, playground games, or choosing food in a cafeteria line
Scanning slow search patterns do not allow them to fully understand the environment around them fast enough to avoid an obstacle, so children with homonymous hemianopia often avoid new environments altogether
socio-emotional well-being. For example, the child may not be chosen for team sports during recess. Because the eyes look normal, other children and teachers may not understand how the visual field loss affects the child. They may think “they are not trying hard enough”. Homonymous hemianopia may be hidden to all.
walking in crowded areas such as sidewalks, shopping malls and supermarkets, classroom hallways and playgrounds, seeing playmates or teammates, identifying and finding objects, crossing the street, reading and learning, and other activities of daily living such as cooking, pouring beverages, and especially driving.
leaving out of important parts of a scene and, consequently, to poor comprehension and social misunderstanding.
Because homonymous hemianopia causes a loss of half the central field of vision, the child only sees part of the word when looking at it. This makes word identification very difficult. The child must scan to see the entire word before reading it, adding an additional step to the process of reading the word. Longer words are never seen as a whole word resulting in various reading accuracy errors. This can include misidentifying a word, omitting letters, syllables, skipping over short words unintentionally, or guessing errors.
Guessing errors can be frequent because the child does not see the entire word. The child may identify the prefix only and then fill in the rest of the word based on prior experience
Children may have problems finding the next line of text or may skip the next line altogether
STRATEGIES
Teach scanning search the lost visual field by turning their head
Children with homonymous hemianopia often require a lot of effort to recognize that there are moving objects, people, or obstacles in their missing visual field.
Uveitis
GENERAL
Inflammation of any part of uveal tract (iris, ciliary body or choroid)
Anterio Uveitis (aka iritis)
Intermediate Uveitis (middle layer) - inflammation involving vitreous gel
Posterior uveitis - inflammation of the choroid
ISSUES
Red, watery eye, pain
Light sensitivity
Blurred vision
Floaters
STRATEGIES
Dilated eye exam
Early treatment before bigger problems: dark glasses, eye drops to dilate pupil and reduce pain, steroid eye drops to reduce inflammation
Vision Testing
VA Snellen Chart (SS, FS) and what for chn? and Amsler Grid (AMD),
VF Static Perimetry look at centre and dots flash up on screen, does 30 degrees nasal / temporal, about half the field (Humphrey)
VF Kinetic Perimetry isopter of different size coming in from sides, 90 degrees nasal / temporal (Goldmann field). Also confrontation 4 sides only.
Imaging…
Optical Coherence Tomography
Electro retinography
Pressure… Applanation tonometers
Visual Acuity:
Snellen Chart … at 6m or 3m with a mirror, record smallest line read accurately (can be less 1 letter) 6/30 -1. If 6/60 can’t be read go 1m closer until can be read, if still not read then go less accurate measurement of count fingers (CF), hand movement (HM), Light perception (LP) - seeing a light switch on and off.
Amsler: grid where person focuses on black dot in middle. If parts of grid appear distorted, blurry, dark or blank it indicates a visual field deficit. Often test for macular degeneration.
Peripheral Vision:
Tested using perimetry: all tests must maintain constant gaze toward fixed location for several minutes, each eye tested separately while opposite eye covers with patch.
Static perimetry: most common, look at centre of illuminate white screen, machine presents flashing lights of different sizes and brightness. Gradually increase size or brightness, press button each time you see light. Very important for monitoring glaucoma. Usually 4-7 min each eye only does central 30 degrees as full field is more time consuming. Print out shows dots black and grey where vision going for each eye. Most popular machines are Humphrey, Octopus, Medmont.
Kinetic perimetry: points of light moved inwards slowly until you see them, location of points , brightness and size of light can be changed, not automated so accuracy depends on person operating it. End up with a series of dot to dot connecting line showing visual field. Normally map neurological field defects rather than monitor glaucoma. Goldmann field.
Confrontation perimetry: simple method for gross field defects. Simply cover one eye, asking patient to look straight ahead while using peripheral vision to identify an object or number of fingers shown by examiner.
Field is only tested at four locations usually. Topographic map showing island of vision
Each healthy eye gives horizontal field of 160 degrees and vertical field of 135 degrees:
100 degrees temporally (toward your ear),
60 nasally (towards nose)
60 degrees superiorly (up)
75 degrees inferiorly (down)
Combined healthy eyes horizontal field of 190 degrees, legal blindness is 20 degrees or less
Macula accounts for about 12 degrees of visual field, fovea about 3 degrees of visual field
Blind spot is ~15 degrees toward your ear (temporally) from centre
Imaging Eye:
Optical Coherence Tomography - scan eye like ultrasound, see individual cells in back of eye to identify and diagnose eye disease. Counts the cables, how many missing, how to fix. Print out with cross section of cells, lots of pictures, numbers etc.
Electro retinography
Eye Pressure:
Handheld device
Slit lamp - Gold standard.
General:
Legal blind = 6/60 or <20 degrees field of vision
6/12 is legal driving limit
