Aviation Vision and Options for Correction Flashcards
Name the two eye parts that perfrom refraction. What percentage of refraction do they contribute?
- Cornea/tear film: 2/3
- Lens: 1/3
Describe myopia
MYOPIA
Cornea Too Steep
Axial Length Too Long
Crystalline Lens Too Powerful
Myopia ( Nearsightedness )
Clear Vision at Near, Blurred Vision at Distance
Most Common Condition in Our Society
Problematic When Present
Relatively Unstable, May Change With Time
Even Small Defects Require Correction
Corrected With Negative ( - ) Lenses
Describe hyperopia.
HYPEROPIA
Cornea Too Flat
Axial Length Too Short
Crystalline Lens Too Weak
Hyperopia ( Farsightedness )
Clear Vision at Distance, Excessive Focus at Near
Less Common Condition in Our Society
Relatively Stable
Crystalline Lens Can Compensate for Low Hyperopia
Corrected With Plus (+) Lenses
Problematic When Over 40 Years Old
Describe astigmatism.
Astigmatism
Common Ametropia Condition
May Change With Age
Affects Vision at All Distances
Eye Can Not Compensate
Cornea not spherical– is football shaped– focal point in 1 of 5 configurations
List 2 mechanisms each of objective and subjective refraction measurement. Describe them.
- Objective– how light rays pass through visual system
- Autorefraction– computer does
- Retinoscopy– human does
- Subjective– measurement of prescription (i.e. better 1 or 2)
- Manifest (dry)– non-dilated
- Cycloplegia (wet)– dilated
Why is cycloplegic refraction obtained?
Removes pt’s ability to focus.
Describe the types of corrective lens shape from refractive correction in myopia, hyperopia and astigmatism.
- Myopia– Divergent/concave (minus lens, i.e. -2.50 Sph)
- Hyperopia– Convergent/convex (plus lens, i.e. +3.50 Sph)
- Astigmatism– Spherocylinder lens
- Cylinder gets images together, lens moves image to retina
- Axis is alignment (rotation of the lens)
Define axis and power in astigmatism.
- Axis- direction of no curvature
- Power- is perpendicular to axis
Draw the axis.
There is no negative axis.
Discuss the two types of cylinder prescriptions.
- Opto uses minus cyclinder for grinding lenses
- Ophtho uses plus cylinder for surgery
Perform minus cylinder conversion.
Perform plus cyclinder conversion.
Perform minus cylinder conversion.
Perform plus cyslinder conversion.
Perform minus cylinder conversion.
+2.00-3.00x090
Perform plus cylinder conversion.
-1.00+3.00x180
Discuss the difference between minus and plus cylinder with respect to minus cylinder?
Minus cylinder is the least minus and plust cylinder is the most minus.
Perform minus conversion.
-1.00-2.00x135
Perform plus conversion.
-3.00+2.00x045