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Optics Zaid > Chapter 1: Properties Of Light > Flashcards

Chapter 1: Properties Of Light Flashcards

1
Q

‘Optical radiation lies between with parts of the electromagnetic spectrum

A

X-ray and microwave

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2
Q

Name the 7 domains of optical radiation

A

-ultraviolet C (UV-C), 200-280 nm
-ultraviolet B (UV-B), 280–315 nm
-ultraviolet A (UV-A), 315–400 nm

-visible radiation, 400-780 nm

-infrared A (IRA), 780–1400 nm
-infrared B (IRB), 1400–3000 nm
-infrared C (IRC), 3000-10000 nm

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3
Q

Wave length range of visible light

A

visible radiation, 400-780 nm

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4
Q

The lens absorbs which part of the electromagnetic spectrum,

A

UVA

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5
Q

The cornea and sclera absorbs which part of the electromagnetic spectrum,

A

UV CB
IR CB

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6
Q

Which part of the electromagnetic spectrum passes through the cornea and lens, causing retinal damage, e.g. eclipse burns

A

IRA 780-1400nm

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7
Q

deuteranopia, protanopia and tritanopia indicate absence of

A

green, red and blue cone function respectively

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8
Q

What is deuteranomaly, protanomaly and tritanomaly

A

Change in sensitivity of the cones

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9
Q

X chromosome encodes which cone pigment?

A

Red/ green
Causing protanopia and deutranopia if lost

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10
Q

Chromosome 7 encodes which cone pigment

A

Blue, causing tritanopea if lost

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11
Q

What is the commonest colour vision anomaly

A

Deutranomoly, due to defect in X chromosome, effecting green colour pigment

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12
Q

Optic neuritis efffects which colours in optical spectrum

A

Red green

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13
Q

Glaucoma and autosomal dominant optic neuropathy effect which part of visual spectrum

A

Blue yellow

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14
Q

Retinal diseases effect which part of the visual spectrum

A

Blue yellow
Expect stutgard which causes red green

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15
Q

Describe Farnsworth–Munsell (FM) hue 100 test

A

Comprises 84 coloured discs, numbered in sequence on the undersurface and divided into four groups of 21. The colours of each group occupy a portion of the colour spectrum. The colours differ only in hue and have equivalent brightness and saturation. Each group must be arranged in a row with the reference colours at each end and the intervening discs in order of closest colour match.

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16
Q

Describe the d15 colour test

A

Arrange colours from one reference colour. Doesn’t pick up small defects

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17
Q

Ishihara plates test for which abnormality

A

Red green
Patients can read patterns by difference in colour as opposed to contrast

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18
Q

Which colour vision test can be used on children?

A

Lanthony New Colour Test

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19
Q

Fluorescein angiography allows you to study which structures

A

Retinal circulation by by photographing the passage of fluorescein through the vasculature after it has been administered systemically.

Can also be used to stain ocular surface, monitor aqueous production, stain structures in light microscopy by flourescine bound to antibodies

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20
Q

How does fluorescine angiography work:

A
  1. White light passes through blue filter and hits the back of the eye. Orange dye fluorescein sodium when excited by blue light (465–490 nm) emits yellow–green light (520–530 nm)
  2. Some light is absorbed, some reflected and some is excited, and is converted to green/ yellow light.
  3. The reflected light passes through a green yellow filter which absorbs blue reflected light, thus only allowing you to see green yellow light from choroidal and retinal vasculature.
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21
Q

Indocyanine Green is used to view

A

Absorbs 805 nm and emits 835 nm infrared radiation. The retinal pigment epithelium does not absorb these wavelengths, and it is therefore possible to observe fluorescence of the choroidal circulation after ICG is administered intravenously.

22
Q

Define coherent and incoherent ligh t

A

Coherent light= in phase
Incoherent light= out of phase

23
Q

What happens when two waves of equal amplitude are out of phase by half a cycle

A

Cancel out, aka destructive interference.

24
Q

Where does destructive interference naturally occur?

A

Stroma of the cornea.

25
Q

Give an example of destructive interference not in the cornea

A

Lens surfaces coating.
The coating consists of a thin layer of transparent material
Light reflected from deep and superficial layers of the lens cancel each other out

26
Q

What is an airy disk

A

When light passes through a circular aperture, a circular diffraction pattern is produced. This consists of a bright central disc surrounded by alternate dark and light rings. The central bright zone is known as the Airy disc.

27
Q

Diffraction is most marked in large or small apertures?

A

Small.
In small pupils, it is the main cause of image imperfection.
However, advantage of large pupil in reducing diffraction is outweighed by the increased effect of spherical aberration

28
Q

Define the limit of resolution/ resolving power

A

The minimum angle at which two objects are distinguishable from one another, aka when an airy disk of an image falls on the first dark circle of another image

29
Q

What is Catford’s drum and what does it assess?

A

It is an objective method to evaluate the objective visual acuity by inducing optokinetic nystagmus in children.

The Catford drum comprises a white cylinder marked with black dots of increasing size corresponding to visual acuities ranging from 6/6 to 2/60 when viewed from 60 cm.

The visual acuity is assessed by reducing the size of the dot until the smallest dot is found that can no longer induce optokinetic nystagmus.

NB, it over estimates acuity.

30
Q

Describe STYCAR and Ivory ball test

A

Balls of varying size are rolled across a surface, 3m away from a child to assess their visual acuity .

31
Q

How to assess visual acuity in pre verbal children?

A

Depend upon preferential looking and the measurement of visually evoked potentials.

Preferential looking can be used to assess the visual acuity of infants based upon their turning their head or eyes towards a patterned rather than a uniform target. A black and white square wave grating (alternating black and white stripes) is presented simultaneously with a plain grey target. Children with better vision are able to see a finer grating and turn towards it.

For VEP, the stimulus used is either a black and white square wave grating or a chequerboard pattern in which the pattern reverses at a set frequency. Electrical impulses are then recorded from the occipital.

32
Q

Define an optotype

A

An optotype is a symbol, the identification of which corresponds to a certain level of visual acuity.

33
Q

How do we use Optotypes to measure children’s acuity

A

Testing of young children requires them to match the optotype letter (STYCAR letter test and Sheridan–Gardiner test) or symbol on a card shown by the examiner who is 6 m or 3 m away by pointing to one of a group of matching letters on a key card. Children aged 18–24 months may be able to perform a picture optotype test (Kay’s and Cardiff picture test).

34
Q

What is the theory behind the Snellen chart?

A
35
Q

Why is LOGMAR more precise than Snellen?

A

LOGMAR has a regular progression in the size and spacing of the letters from one line to the next and the same number of letters on every line. Comparable results are therefore possible at any test distance.

36
Q

What does 20/20 vision signify

A

From 20 feet (numerator), the patient can read all of line 20 (denominator).

37
Q

What is vernier acuity

A

Hyperacuity, using cortical processing, allowing you to detect an offset of 3-5 arc seconds as opposed to a minute.

38
Q

How to test Near Visual Acuity

A

The near visual acuity is usually tested at a distance of 25–33 cm. Near acuity charts usually comprise unrelated words or passages of text.

39
Q

Potential visual acuity

A

These tests may be used to assess the potential visual acuity of eyes in which it is not possible to see the macula e.g. cataract

The blue field entoptic phenomenon is the ability to see moving white dots when blue light diffusely illuminates the retina. They are thought to represent light transmitted by white blood cells in the perifoveal capillaries. When this phenomenon is present, macular function is grossly intact.

40
Q

How to test for contrast sensitivity

A

Pelli–Robson contrast test chart displays letters that have decreasing levels of contrast to their background.

The VISITECH chart has 40 circles with different sine wave gratings and levels of contrast. The subject must indicate the orientation of the circles.

41
Q

When light is reflected from a surface such as water and is polarised, what plane is it polarised in?

A

The plane of polarisation of the reflected light from a surface is parallel with the surface.

42
Q

What is a Dichroic substance?

A

The molecular structure of dichroic substances completely blocks transmission of light waves not aligned with its structure by absorption. Thus, only one beam of polarised light emerges, much weakened in intensity compared with the incident non-polarised light.

43
Q

Define stereopsis

A

Ability to fuse 2 slightly different images hitting 2 different bits of the retina, to be seen in 3d.
Measured in arc seconds

44
Q

Stereoacuity of more than 250 arc seconds is an indicator of potential…

A

Amblyopia.
Normal is 60 seconds or less, when both images hit the macula

45
Q

Describe the Titmus test

A

Test of stereoacuity. Have to wear binoculars with Polaroid glasses with different lenses in each eye. You look at a target from 40 cm away which have 2 images that are superimposed onto each other. Because of the Polaroids, each eye sees a slightly different image. Test stereoacuity between 3000to 40 seconds. Biggest image is a fly.

46
Q

Describe the frisby test

A

Test for stereoacuity. Does not require glasses.

4 glass plates off different thickness. Each has 4 squares with random patterns. One square has a hidden circle printed on the back. Usually viewed from 40cm. But if you adjust viewing distance, you can get an acuity test of 15 seconds.

47
Q

Describe TNO test

A

TNO also tests stereoacuity and uses red green glasses.
Circles appear on a white back ground in green an red. Green dot seen by red glasses lens as black. The green dot is not see.
Red dot seen as black by green lens. Red dot is not seen.

48
Q

Describe Lang stereo test

A

Does not require glasses

Hold cards at normal reading length, asked if they can see objects. Each eye sees something slightly different due to built in cylindrical lens

49
Q

When quantifying light in radiometric terms, what is:
- radiant flux
- radiant intensity
- irradiance
- radiance

A
  • how much light is emitted from a source (radiant flux)
  • intensity (radiant intensity)
  • the amount falling on a surface (irradiance)
  • Light reflected from a surface (radiance). The equivalent photometric
50
Q

The total flow of light emitted in all directions from a source is termed

A

The total flow of light emitted in all directions from a source is termed either the radiant flux, if measured in watts, or luminous flux, if measured in lumens

51
Q

What is Automated Perimetry

A

Test for visual field. Perimetry measures the light sensitivity of points on the retina by the ability of the patient to detect light stimuli of varying intensity presented at corresponding points in the visual field. Currently, most perimeters have a standard background luminance of 31.5 apostilbs (asb)

52
Q

Recall units of light measurement

A

Optics Zaid (17 decks)

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