Chua 2 Flashcards
How can chromatic aberration be reduced?
Combining different materials in optical system e.g. crown glass and flint glass
What is the duochrome test sensitive to?
Changes in refraction of 0.25D or less
What is the duochrome useful for?
Useful in myopic patients to avoid overcorrection which can cause the eye to accommodate causing eye strain
How can oblique astigmatism be reduced
Meniscus lens
Pantoscopic tilt
What are best form lenses?
Made to reduce spherical and oblique aberration
What are high order aberrations?
Cannot be corrected by simple spherocylindrical systems such as specs/CLs
Caused by minute misalignments of the eyes optical components include spherical aberration, coma, high order astigmatisms
Can be detected with wavefront analysis by aberometer
Cornea power
Lens power
Cornea 43.05
Lens 19.11
Eye 58.64
What is back vertex powe
Reciprocal of the posteiror vertex focal length in D
In a convex meniscus lens, what is stronger back or front vertex power?
Back vertex power as posteiror vertex focal length is shorter htan second focal length and anterior vertex focal length
What is range of accommodation?
Distance between far point and near point
What is normal accommodative convergence/accommodation ratio?
3:1 to 5:1
What methods can be used to calculate AC/A ratio? Which requires IPD
Heterophoria (requires IPD)
Gradient (does not)
Heterophoria gives higher ratio
What is esotropia with high AC/A ratio worse
For near than distance
Captoptric images
1, 2, 3 - virtual, erect (reflection in convex mirror)
4 - real, inverted (reflection in concave mirror)
What hypermetropia cannot be overcome by accommodation?
Absolute (in excess of amplitude of accommodation)
