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Year 2 > ATOL/TOD Definitions > Flashcards

ATOL/TOD Definitions Flashcards

1
Q

Spherical aberrations

A

Occurs when parallel light is incident on the surface or when light comes from a near object places on the optical axis

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2
Q

Coma

A

Occurs when light is incident obliquely on a lens surface

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3
Q

Coma

A

Occurs when light is incident obliquely on a lens surface

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4
Q

Curvature of field

A

Occurs when oblique astigmatism has been eliminated

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5
Q

Curvature of field

A

Occurs when oblique astigmatism has been eliminated

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6
Q

Distortion

A

Occurs when all other aberrations are eliminated, caused by the stop

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7
Q

Oblique astigmatic error (OAE)

A

Dioptric distance between the tangential and sagittal image planes

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8
Q

Oblique astigmatic error (OAE)

A

Dioptric distance between the tangential and sagittal image planes

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9
Q

Mean oblique power (MOP)

A

The dioptric distance of the disc of least confusion from the vertex sphere

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10
Q

Mean Oblique error (MOE)

A

The dioptric difference between MOP and BVD

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11
Q

Best form lenses

A

Oblique astigmatism must be corrected to for a point image
MOE must be corrected
Distortion and chromatic aberrations kept to a minimum

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12
Q

Point focal lenses

A

Form a point image of an off-axis object

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13
Q

Percival lenses

A

The disc of least confusion is placed on the far point sphere, the tangential and sagittal image shells lying either side of the

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14
Q

Vertex distance

A

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

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15
Q

Fresnel prism

A

Non-permanent
Material - PVC
Reduced VA’s by two lines
Applied under water
1mm thick
Made of ridges
Easily dirty
Up to 40D

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16
Q

Ghost images

A

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

17
Q

Increased robustness

A

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

18
Q

Jump

A

Sudden upwards movement of the image when looking through the dividing line of bifocal

19
Q

Mechanical requirements (bifocal)

A

Permanent
Lightweight
Invisible

20
Q

Optical requirements (bifocal)

A

Best vision
No prismatic effect
Minimal jup

21
Q

Solid bifocal

A

Ground from single piece of material
ADD is produced by grinding second curve on front surface

22
Q

Fused bifocal

A

Made from two pieces of different refractive indices
Depression worked into front
Button is fused into depression at high temp
Smooth finish

23
Q

Near vision effectivity error (NVEE)

A

Error in power produced to a near object position
Changes with lens form
Problematic in high hyperopes

24
Q

Ring scotoma

A

Produced in high hyperopes
Dividing line of bifocals
Loss of field
Caused by prismatic effect
Results in jack-in-the-box effect

25
Q

Field of view

A

The angle subtending the linear field of the eye

26
Q

Apparent field of view

A

Angle subtending the eyes centre of rotation by an empty frame aperture

27
Q

Real field of view

A

The angle subtended by the effective diameter of a lens conjugate with the eyes centre of rotation

28
Q

Complete interference

A

When two coherent waves are half a wavelength out of phase; the trough of one ave coincides with the crest of another

29
Q

Complete destructive interference

A

When the crest of one wave falls on the trough of another and cancel each other out

30
Q

Path condition

A

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

31
Q

Amplitude condition

A

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

32
Q

Amplitude condition

A

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

33
Q

MAR methods of manufacturing

A

Traditionally by evaporation in a vacuum chamber

Year 2 (6 decks)

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