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36 Cards in this Set
- Front
- Back
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Pathway of light
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from external starting at the cornea to internal (retina)
light enter through cornea, aqueous humor & pupil, crystalline lens, vitreous humor and the converges on the retina |
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Average length of healthy adult eye
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2.42 cm
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fixed refracture power of the cornea
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43 diopters (70% of total refractive power of the eye)
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refractive power of the natural lens
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20 diopters
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Myopia
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nearsightedness
caused by a highly steep cornea or long distance between cornea and the retina light rays come up short. muscle weakness |
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Hyperopia
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Farsightedness
caused by a shorter distance from cornea to the retina light rays go too far |
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Astigmatism
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when cornea curvature is more oval than round.
Both distant and near vision are affected |
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Role of additives in contact lenses
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copolymerized in the contact lens material to protect eye from harmful effects of UV light
UV light is harmful to retina and contributes to cataract |
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catarct
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clouding or discoloration of the lens
one of the most common eye disease |
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Optical devices
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good transmission of visible light and ultraviolet light-absorbing
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Important properties of contact lenses
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oxygen permeability
hydrophilic |
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Materials to make contacts
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polydimethylsiloxans PDMS
polymethyl phenyl vinyl silosanes PMPVS silicon rubber is hydrophobic so must be treated with an RF-plama reactor to make surface hydrophilic (not good material) |
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Standard Hydrogel Contact Lenses (SHCLs)
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homogeneous hydrogel
material: poly(2-hydroxethylmethacrylate) (PHEMA), 40% of water hydration in physiological saline solution Advantages: fit snugly to cornea, increase coefficient of oxygen permeability with water content complications: oxygen transmissibility of oxygen decreases with increasing thickness |
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4 groups of FDA classified hydrogel lenses
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1) low water (<50% H2O) nonionic
2) High water (>50% H2O) nonionic 3) Low water, ionic 4)High water, ionic |
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Siloxane-Hydrogel Contact Lense
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Material: silicone and treated with RF-plasma reactor
Advantage: High O2 permeability Complications: |
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3 layers of the cornea
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1) Epithelium, outermost layer, 5 cell layer
2)Stroma, main portion. 78% hydrated in normal state 3) The endothelium, intermost layer, maintains hydration of the cornea |
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Hypoxia
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an injury to the epithelial and endothelial membranes that disrupts normal corneal hydration
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Describe a corneal transplant
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cone-shaped cornea is removed and replaced with a donated cornea.
90% success rate (no blood in cornea) 60% still require glasses or contacts |
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Intracorneal Implants
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used to correct vision
materials: hydrogel, silicone rubber previous implants were made of PMMA or polysultane which resulted in ulcerations |
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Corneal Ring implants
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half circle implants placed in the clear, dome-shaped bulge at the front of the cornea. (placed on the sides of the cornea) complications: infection, glare or halos, night vision problems and overcorrection or undercorrection |
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Corneal ring implants effect on curvature
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steeper, increases the refractive power
flatter, decreases the refractive power |
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Keratomileusis
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removes a section of the cornea, reshapes that section, and the replaces the reshaped section
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Intrastromal Ablation
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laser sculpts under surface to correct vision
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Epithelial Implants
(Epikeratoprostheses |
replaces irregular, swelling, and proliferated epithelium.
material: hard PMMA and glued with cyanoacrylate |
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Epikeratophakia
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Impantation of artificail epithelial or transplant beneath the epithelium to increase the steepness of the cornea for correction of farsightedness
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Artificial Endothelium
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replaces corneal endothelium with silicon rubber membrane that passively controls hydration
a failure as it prevented cornea from receiving nutrient and water from aqueous humor |
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Removing cataract
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cataract is removed, the lens of the eye is removed. An artificial lens into the eye to help it focus
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age-related cataract
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cataract related to aging
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congenital cataract
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born with cataract or developed in childhood. May or may not affect vision
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Secondary cataract
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cataracts developed because of medical problems or medications. Long-term unprotected exposure to sunlight may also lead to cataracts
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Traumatic cataract
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Develops soon after or years later after eye injury
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Symptoms of a Cataract
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-fading or yellowing of eye
-double or multiple vision in one eye, may go away as cataract grows -needing brighter light to read -cloudy or blurry vision -poor night vision |
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Intraocular Lens Implants (IOLs)
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10 million IOLs are implanted worldwide
used in cataract patients Helps focus light, without it the person would be illegally blind after cornea removal |
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cararactous
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lens of eye turns cloudy and optical images deteriorates. Eventually leads to blindness and is leading cause of blindness
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LASIK for Nearsightedness
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a thin flap of cornea is created and folded back
Excimer laser is applied to reshape the cornea the cornea flap is replaced over the treated cornea the flatter cornea now bends the light onto the retina |
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LASK for Farsightedness
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a thin flap of cornea is created and folded back
Excimer laser is applied to reshape the cornea the cornea flap is replaced over the treated cornea the steeper cornea now bends the light onto the retina |
