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Basic information about vision
Anatomy of the EyePupil- how much light enters the eye
Ciliary body- changes the shape of the lens (focusing)
Choroid- contains vessels that supply blood
Retina- contains the cells that are sensitive to light (rods and cones)
Lens- focuses light to the back of the eye
Sclera- the white part of the eye
Optic nerve- transmits visual information to the brain
Cornea- the transparent layer at the front of the eye |
Components of SightVisual Acuity | the level of detail a person sees | Visual Field | the total area one sees in a single view | Contrast Sensation | the ability to distinguish shades of light, dark, and similar colors | Light Modulation | the ability to adapt to changing light conditions | Visual Perception & Interpretation | the processing of information once it reaches the brain |
Macular Degenerationa group of conditions that cause central vision loss | Macular degeneration (AMD) is when the retinal pigment epithelium (RPE) layer begins to malfunction. | Most AMD starts out as dry and some progress to wet | Dry AMD is the build up of deposits called drusen, which causes macular scarring | Wet AMD is the development of a cluster of blood vessels under the macula |
CataractsCataract is the clouding of the crystalline lens in your eye | Cataract surgery is one of the most common surgeries performed | If left untreated, the cataract will dull color and blur vision | Clients with cataracts will have decreased contrast sensitivity |
| | Hierarchy of Visual Perceptual Processing
Refractive ErrorMyopia | the problem with the lens ability to focus on the image with adequate power; the power is not strong enough resulting in undershooting the fovea/retina (focal length is too short) | concave or negative (-) lens | Hyperopia | problem with the lens ability to focus on the image with adequate power; power is too strong and overshooting the fovea (focal length to too long) | convex or positive (+) lens | Astigmatism | the shape of the cornea itself is misshaped impeding the ability to properly bend or refract light/image resulting in a distorted image | misshaped cornea |
Refactive Error is due mishaped What does 20/20 mean?You can see at 20 feet as a person with standard vision can see at 20 feet |
Diabetic RentiopathyDiabetes causes damage to small blood vessels and the eye is not spared | DR causes a number of different visual problems ranging from "floaters" to total blindness | Background diabetic retinopathy is the early stage of DR | Proliferative diabetic retinopathy is a more severe form of DR. |
| | What is low vision?Low vision is defined as a visual impairment that cannot be corrected by medical or surgical intervention and is severe enough to interfere with the performance of activities of daily living but allows some usable |
Four Types of Vision LossCentral Field Loss | Age-related Macular Degeneration (AMD) or Stragardts Macular Degeneration (genetic) | Peripheral Field Loss | Glaucoma or retinitis pigmentosa | Visual Field Cuts | Neurological conditions stroke, brain injury, Parkinson's, and Multiple sclerosis | Diffuse Vision Loss | Usually caused by diabetic retinopathy |
Functional Implications of Central FieldDifficulty reading | Decreased contrast sensitivity (e.g. poor detailed vision) | Excessive head movement to search for items in their environment or during reading | All things that require detailed vision will be affected (e.g. reading bills, text messages, following recipes, driving, etc) | Self care is NOT affected |
GlaucomaGlaucoma is caused by increased pressure in eye | Glaucoma causes peripheral vision loss and will untreated can cause blindness | Fortunately, glaucoma is very treatable with eye drops and surgery | The key to treatment is catching it before it damages the optic nerve and cause vision loss |
How people see with glaucoma
Retinitis Pigmentosa (RP)Retinitis pigmentoas is a progressive hereditary eye disease that causes deterioration of the retinal cells | People usually start noticiting that they have night blindness, then they start losing their peripheral vision | Central vision is spared in the beginning, but the visual flieds so small that they can only see small pinholes | RP will eventually cause total blindness |
Retinitis pigmentosa image
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