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
Discuss 3 rules of how axis is written.
- Always 90 degrees between minus and plus
- Always positive
- Always written as three numbers
Perform minus conversion.
+1.00-3.00x045
Perform plus conversion.
-2.00+3.00x135
How is this prescription written?
-2.00 Sph (DS)
The DS is written to indicate that the cylinder is not forgotten.
List the three rules for simple transposition between minus and plus cylinder.
- Add sphere and cylinder
- Change sign of cylinder
- Change axis by 90 degrees
Transpose:
+2.00-1.00x180
+1.00+1.00x090
Transpose:
-0.50-1.50x090
-2.00+1.50x180
Transpose:
-3.25-1.25x010
-4.50+1.25x100
Transpose:
+3.50-3.50x040
Pl+3.50x130
Traspose:
+1.00+1.00x090
+2.00-1.00x180
Transpose:
Pl+3.50x130
+3.50-3.50x040
Transpose:
-2.00-1.50x180
-0.50-1.50x090
Transpose:
-4.50+1.25x100
-3.25-1.25x010
What are the IFC I standards?
- +2.00 to -1.50 in any meridian
- 1.50D max astigmatism
Write as minus and plus cylinder.
Does this candidate meet IFC I standards?
- +1.25-1.00x180
- +0.25+1.0x090
- Yes (+2.00 to -1.50 D in any meridian, 1.5 D max astigmatism)
Write as minus and plus cylinder.
Does this pt meet IFC I standards?
- +1.25+1.00x180
- +2.25-1.00x090
- No (+2.00 to -1.50 D in any meridian, 1.5 D max astigmatism)
Write as minus and plus cylinder.
Does this pt meet IFC I standards?
- -1.25-1.00x180
- -2.25+1.00x090
- No(+2.00 to -1.50 D in any meridian, 1.5 D max astigmatism)
Write as minus and plus cylinder.
Does this pt meet IFC 1 standards?
- +1.25+1.75x180
- +3.00-1.75x090
- (+2.00 to -1.50 D in any meridian, 1.5 D max astigmatism)
Define anisometropia. Why does it matter?
Refractive difference between the eyes. Matters because if the difference is too large, then uneven image sizes, which affects depth perception.
Define OD and OS.
- OD- right (dexter)
- OS- left
Right is always written above left
Why are there authorized frames for aircrew?
Compatability with head mounted equipment.
List 4 characteristics of aircrew spectacles that are not authorized.
- Polarized lenses (can’t see display)
- Progressive lenses (causes distortion)
- Commercial sunglasses
- Colored lenses (alters color perception)
List 3 criteria for SCL such as to not require a waiver.
- Meet vision standards while wearing SCL
- No more than 2.00D astigmatism
- Must carry back up glasses while in flight
Describe the water contect on approved SCL? Why?
- Less than 60%
- To prevent dehydration
List two types of vision correction prohibited for the SCL program
- No monovision contacts (i.e. one eye with distance and one eye for near)
- No bifocal contacts
What is the requirement for when approved SCL must be worn?
- FCI– at all times
- All others, only for inflight duties
List 4 complications associated with contact lens overwear. How do they present?
- GPC (giant cell papillary conjunctivitis)– is an allergic response (bumpy upper eye lid)
- CLARE (contact lens acute red eye)– watery, irritated, blurred vision
- Corneal neovascularization (usually asx, unless take out contact)
- Corneal ulcer (mod to severe pain, photophobia, blurred vision)
What do you have to do if a patient has a complication?
File an incident report
