ATOL/TOD Definitions Flashcards
Spherical aberrations
Occurs when parallel light is incident on the surface or when light comes from a near object places on the optical axis
Coma
Occurs when light is incident obliquely on a lens surface
Coma
Occurs when light is incident obliquely on a lens surface
Curvature of field
Occurs when oblique astigmatism has been eliminated
Curvature of field
Occurs when oblique astigmatism has been eliminated
Distortion
Occurs when all other aberrations are eliminated, caused by the stop
Oblique astigmatic error (OAE)
Dioptric distance between the tangential and sagittal image planes
Oblique astigmatic error (OAE)
Dioptric distance between the tangential and sagittal image planes
Mean oblique power (MOP)
The dioptric distance of the disc of least confusion from the vertex sphere
Mean Oblique error (MOE)
The dioptric difference between MOP and BVD
Best form lenses
Oblique astigmatism must be corrected to for a point image
MOE must be corrected
Distortion and chromatic aberrations kept to a minimum
Point focal lenses
Form a point image of an off-axis object
Percival lenses
The disc of least confusion is placed on the far point sphere, the tangential and sagittal image shells lying either side of the
Vertex distance
Front of cornea to back of lens
Increases, becomes more plus
BS 2738 BVD over +/-5.00
Average 8-12mm
Feff=F/1dF
Compensate 1mm
Fresnel prism
Non-permanent
Material - PVC
Reduced VA’s by two lines
Applied under water
1mm thick
Made of ridges
Easily dirty
Up to 40D
Ghost images
Five ghost images
May be troublesome
Formed by bright sources surrounded by lower illumination
1 - internal reflection (most troublesome)
2 - corneal reflection on back surface
3 - corneal reflection on front surface
4 - reflections from behind on back surface
5 - reflections behind on front surface
Increased robustness
Four classes on mechanical strength (F, A, B, S)
Polycarbonate/ trivex
Thermally toughened
Steel ball bearing - 22mm 43g
BSEN 16321 protection for occupational use
BSEN 19734 guidance on use/ selection
Jump
Sudden upwards movement of the image when looking through the dividing line of bifocal
Mechanical requirements (bifocal)
Permanent
Lightweight
Invisible
Optical requirements (bifocal)
Best vision
No prismatic effect
Minimal jup
Solid bifocal
Ground from single piece of material
ADD is produced by grinding second curve on front surface
Fused bifocal
Made from two pieces of different refractive indices
Depression worked into front
Button is fused into depression at high temp
Smooth finish
Near vision effectivity error (NVEE)
Error in power produced to a near object position
Changes with lens form
Problematic in high hyperopes
Ring scotoma
Produced in high hyperopes
Dividing line of bifocals
Loss of field
Caused by prismatic effect
Results in jack-in-the-box effect
Field of view
The angle subtending the linear field of the eye
Apparent field of view
Angle subtending the eyes centre of rotation by an empty frame aperture
Real field of view
The angle subtended by the effective diameter of a lens conjugate with the eyes centre of rotation
Complete interference
When two coherent waves are half a wavelength out of phase; the trough of one ave coincides with the crest of another
Complete destructive interference
When the crest of one wave falls on the trough of another and cancel each other out
Path condition
Reflective waves should be exactly half a wavelength out of phase, which occurs when the optical thickness of the coating applied is exactly one quarter of a wavelength
Amplitude condition
The amplitudes of each of the reflected rays must be the same. They can occur when the refractive index of the coating is equal to the square root of the refractive index of the material
Amplitude condition
The amplitudes of each of the reflected rays must be the same. They can occur when the refractive index of the coating is equal to the square root of the refractive index of the material
MAR methods of manufacturing
Traditionally by evaporation in a vacuum chamber
