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Clinical Optics (Elkington) > Chapter 1: Properties of Light and Visual Function > Flashcards

Chapter 1: Properties of Light and Visual Function Flashcards

1
Q

How many wavebands is optical radiation divided in to? Name the wavebands and their respective lengths.

A 
7 (200nm-10,000nm)
200-280nm - Ultraviolet C (UV-C)
280-315nm - Ultraviolet B (UV-B)
315-400nm - Ultraviolet A (UV-A)
400-780nm - Visible radiation
780-1400nm - Infrared A (IRA)
1400-3000nm - Infrared B (IRB)
3000 - 10000nm - Infrared C (IRC)
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2
Q

Optical radiation lies between what on the electromagnetic spectrum.

A

X-rays and microwaves.

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3
Q

What do each of the optic radiation wavebands have in common?

A

They elicit similar biological reactions.

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4
Q

The ……… the wavelength, the greater the energy of the individual photons of optical radiation.

A

Shorter.

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5
Q

What do the cornea and sclera absorb essentially all of?

A

The incint optical radiation at very short wavelengths in the ultraviolet (UV-B, UV-C) and long wavelengths in the infrared (IR-B, IR-C).

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6
Q

What waveband does the crystalline lens absorb?

A

UV-A

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7
Q

What happens to wavelengths in the range 400-1400nm (visible light and near infrared)?

A

Passes through the ocular media and falls onto the retina.
Visible wavelengths - stimulate retinal photoreceptors giving sensation of light
Infrared A - may give rise to thermal effects.

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8
Q

How may thermal burns occur?

A

The refractive surfaces of the eye focus the incident infrared radiation on the retina, potentially causing retinal damage.

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9
Q

The visible wavelengths of the electromagnetic spectrum are between …..?

A

400-780nm

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10
Q

How is the colour of any object determined?

A

By the wavelength emitted or reflected from the surface of that object.

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11
Q

What is white light?

A

Mixture of wavelengths of the visible spectrum.

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12
Q

What is colour perceived by?

A

Three populations of cone photoreceptors in the retina which are sensitive to light of short (blue), middle (green) or long (red) wavelengths.

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13
Q

How may a congenital colour vision defect occur?

A

If a cone pigment is absent or if there is a shift in the spectral sensitivity.

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14
Q

What is deuteranopia?

A

Absence of green cone function.

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15
Q

What is protanopia?

A

Absence of red cone function.

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16
Q

What is tritanopia?

A

Absence of blue cone function.

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17
Q

What is deuteranomaly?

A

Shift in green cone sensitivity.

18
Q

What is protanomaly?

A

Shift in red cone sensitivity.

19
Q

What is tritanomaly?

A

Shift in blue cone sensitivity.

20
Q

What carries the genes encoding for red and green pigment?

A

The X-chromosome.

21
Q

What carries the gene encoding for the blue pigment?

A

Chromosome 7.

22
Q

What is the prevalence of a defect of the green/red system in men?

A

8%

23
Q

What is the prevalence of a defect of the green/red system in women?

A

0.5%

24
Q

What is the most common colour system defect, and how frequently does this occur?

A

Deuteranomaly (5% men, 0.3% women)

25
Q

How common are Tritan defects?

A

Rare.

26
Q

Acquired optic nerve disease typically causes which colour defects?

A

Red-green defects.

27
Q

Glaucoma and autosomal dominant optic neuropathy typically cause which colour deficit?

A

Blue-yellow deficits (visual field loss in glaucoma may be detected earlier if perimetry is performed using a blue light stimulus on a yellow background).

28
Q

Acquired retinal disease tends to cause which colour deficits? What is the exception?

A

Blue-yellow deficits are typical.

The exception is cone dystrophy and Stargardt’s disease which predominantly cause red-green defect).

29
Q

Clinical tests of colour vision are designed to be performed under what conditions?

A

In illumination equivalent to afternoon daylight in the northern hemisphere.

30
Q

Describe the Farnsworth-Munsell (FM) hue 100 test.

A
  • Most comprehensive test of colour vision.
  • 84 coloured discs.
  • Numbered in sequence on the undersurface and divided into 4 groups of 21.
  • Colours of each group occupy a portion of the colour spectrum
  • 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 (pilot cap) and the intervening discs in order of closest colour match.
  • Placement order indicated nature of colour defect
31
Q

Describe the D-15 test.

A
  • Test of colour vision.
  • Uses colours from all parts of the spectrum which must be arranged in order from a single reference colour.
  • Does not distinguish mild colour defects, but for most purposes those passing the test are nlikely to have problems with hue discrimination.
32
Q

What is Ishihara and what is it useful for?

A
  • Ischihara pseudoisochromatic test plates specifically test for congenital red-green defects (most common abnormality)
  • Random spots of varying isochromatic density.
  • Number or wavy lines represented by spots of different colours
  • ## Figures can only be distinguished from their background by their colour and not by a difference in contrast.
33
Q

What is the Lanthony New Colour Test useful for?

A
  • Tests hue discrimination

- Can be used by children

34
Q

Newly aphakic patients frequently remark that ‘everything looks bluer than before the operation’. Why is this so?

A
  • Retinal photoreceptors are also sensitive to wavelengths between 400-350nm (UV-A).
  • These wavelengths are usually absorbed by the lens of the eye.
  • In aphasic eyes of pseudophakic eyes with intraocular implants without UV filter, such UV radiation gives rise to the sensation of blue or violet colours.
35
Q

What is fluorescence?

A

The property of a molecule to spontaneously emit light of a longer wavelength when stimulated by light of a shorted wavelength.

36
Q

How is the property of fluorescence useful in ophthalmology? Give 2 examples.

A

The orange dye fluorescein sodium, when excited by blue light (465-490nm) emits yellow-green light (520-530nm).
Uses include:
- Fluorescein angiography
- Staining ocular surface defects
- Anterior segment angiography
- Measurement of aqueous humour production and outflow
- In light microscopy, the localisation of tissue constituents using fluorescein bound to specific immunoglobulin.

37
Q

Describe fluorescein angiography.

A
  • Allows the state of retinal and choroidal circulation to be studied by photographing the passage of fluorescein through the vasculature after it has been administrated systemically.
  • White light from the flash unit of a fluorescein camera passes through a blue ‘excitation’ filter to illuminate the funds with blue light.
    The wavelengths transmitted by the excitation filter approximate to the absorption spectrum of fluorescein.
  • Most of the light is absorbed, some is reflected unchanged, some is changed to yellow-green light by fluorescence
  • The blue reflected light and yellow-green light leaving the eye are separated by a yellow-green barrier filter in the camera.
  • This blocks the blue light and exposes the camera film only to yellow-green light from the fluorescein, thereby delineating vascular structures and leakage of dye.
38
Q

What is pseudofluorescence and when does it occur?

A
  • Occurs if there is an overlap in the spectral transmission of the excitation and barrier filters.
  • Allows reflected wavelengths at the green end of blue to pass through the barrier filter and appear as fluorescence.
39
Q

What is Indocyanine green (ICG) dye?

A

A fluorescent substance which absorbs 805nm and emits 835nm infrared radiation.

40
Q

How is Indocyanine green (ICG) dye useful? Name 2 uses.

A
  • The retinal pigment epithelium does not absorb these wavelengths (805nm), and it is therefore possible to observe fluorescence of the choroidal circulation after ICG is administered intravenously.
    (1) May delineate occult choroidal neovascularisation not visible with fluorescein
    (2) Can photosensitise vascular lesions to diode laser photocoagulation.
41
Q

What percentage of 805nm radiation absorbed by ICG is emitted?

A

Only 4% (compared to total fluorescence of fluorescein)

Clinical Optics (Elkington) (1 decks)

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