Test 1  (Properties of light and visual function )

1. With regard to optical radiation:

a. the wavelengths of visible light lies between 400nm 
    and 780nm

b. ultraviolet A has a shorter wavelength than ultraviolet C

c. the shorter the wavelength the higher the energy of an 
    individual quanta (photon)

d. the crystalline lens is better at absorbing shorter than 
    longer wavelengths

e. eclipse burn is caused by infrared radiation
 

Answera.T   b.F   c.T    d.T   e.T
Visible light contains wavelengths between 400 and 
780nm. Ultraviolet A has wavelength of 315-400nm whereas ultraviolet C 200- 280nm. Thus in order of increasing wavelengths: ultraviolet C, ultraviolet B, ultraviolet A; infrared A, infrared B and infrared C. 
The lens is very efficient at absorbing ultraviolet than infrared light. The thermal burn in eclipse burn is caused by infrared light. 
 
 

2. The following are true about colour vision:

a. deuteranomaly is more common than deuteranopia

b. blue pigment gene is found on chromosome X

c. red-green defect is common in acquired optic 
    nerve disease

d. blue-yellow defect is common in glaucoma 

e. blue cone is sensitive to shorter wavelength than green 
    cone
 

Answera.T  b.F  c.T  d.T  e.T
 Deuteranomaly is the most common type of congenital colour defect and is found in 5% of the male population.
 It occurs when the normal middle-wavelength (ie. green) cone photopigment is replaced by one that has a peak
sensitivity at a longer wavelength (ie. red). Deuteranopia
refers to absent of the middle-wavelength ie. green cone.
Blue pigment gene is found on chromosome 7 whereas red and green pigment gene on chromosome X. Red-green defect is seen in acquired optic nerve disease, cone dystrophy and Stargardt's disease. Blue-yellow defects in most retinal dystrophy. Blue-yellow defect in glaucoma and autosomal dominant optic neuropathy.
 
 

3. In colour vision testing:

a. the Fransworth-Munsell hue 100 test contains 84 
    colour discs

b. the colours of the Fransworth-Munsell hue 100 test 
    differs in hue and saturation

c. Ishihara test plates are designed mainly for congenital 
    red-green colour defects.

d. Ishihara test plates can not be used by pre-verbal 
    children

e. Lanthony New Colour Test is only suitable for adults
 

Answer
a.T   b.F  c.T   d.F  e.F
Fransworth-Munsell hue 100 test contains 84 colour discs to be arranged in order of closest colour match. 
The colours only differ in hue with same brightness and 
saturation. Ishihara test plates are mainly for congenital 
red-green colour defect. Wavy lines are used in Ishihara plates for illiterates or children. Lanthony New Colour Test can be used in children.
 

4. With regard to light scattering:

a. it does not occur in vacuum

b. it is proportionally to the the wavelength of the light

c. vitreous is best viewed with light of short wavelength 
    as it scatters more

d. the cornea scatters about 10% of the incoming light

e. it is responsible for poor vision in corneal oedema

Answer
a.T   b.F  c.T  d.T  e.T
Scattering occurs due to the presence of particles within in a medium and does not occur in vacuum. Scattering is inversely proportional to the wavelength of the light ie. the shorter the wavelength the more the scattering. Vitreous is best viewed with short wavelengths such as blue or green light as they scatter more within in the vitreous. Normal cornea scatters about 10% of incoming light which increases with oedema.
 
 

5. The following equipment are used in fluorescein angiography:

a.  a fundus camera with optics similar to 
     direct ophthalmoscope

b. a filter that allows exciting light less than 510nm

c. a filter that allows exciting blue light

d. a filter in front of the photographic film or 
    the digital camera that blocks blue light

e. a filter in front of the photographic film or the digital 
    camera that blocks light of less than 510nm

Answer
a.F   b.T  c.T  d.T  e.T
Sodium fluorescein absorbs blue light light of 465-490nm
and releases fluorescent yellow-green light (520-530nm). The fundus camera has optics similar to indirect ophthalmoscope.

 

6. The following are true about indocyanine green angiography (ICG):

a. indocyanine green has a larger molecule than sodium 
    fluorescein.

b. indocyanine green emits light in the infrared range

c. ICG is better at visualizing the choroidal vasculature 
    than sodium fluorescein angiography because it has a 
    higher protein binding and only partially absorbed by 
    the retinal pigment epithelium

d. ICG is best imaged with photographic film

e. ICG should be avoided in patients with seafood allergy
 

Answer
a.T   b.T   c.T   d.F   e.F
Indocyanine green has a larger molecule than sodium 
fluorescein and more firmly bound to the serum protein.
It is therefore better at visualizing choroidal vasculature. It emits light in the infrared range which is better imaged with digital camera than photographic film. ICG contains iodine and should be avoided in patients allergy to other radiographic contrast dye. Seafood allergy is related to protein and not iodine and therefore not a contraindication.
 

7. Regarding diffraction:

a. it is best explained with the wave theory of light

b. it occurs when there is an obstruction to the light

c. both constructive and destructive interference occurs 

d. it increases with longer wavelength

e. it prevents the formation of a point image from a point 
    source

Answer
a. T   b.T   c.T   d.T   e.T
Diffraction is best explained with the wave theory of light. It occurs when light passes through the edge
of an obstacle such s the pupil. Interference occurs both constructive and destructive. Diffraction depends on several factors: the wavelength of the light, shorter wavelength causes less diffraction than a longer one and
the shape and size of the obstacle for example a smaller pupil causes more diffraction than a large one. A point source is converted by diffraction into a diffraction pattern rather than a point image.

8. The Airy's disc:

a. is formed by diffraction

b. contains a central bright disc that receives 90% of the 
    luminance flux

c. is surrounded by concentric light and dark rings

d. is proportional to the wavelength of the light

e. is proportional to the diameter of the pupil
 

Answer
a.T   b.T   c.T   d.T   e.F
The Airy's disc is a diffraction pattern when light passes through the edge of an obstacle. It contains a bright central disc ie. Airy's disc that receives about 90% of the luminous flux. This disc is surrounded by concentric
light and dark rings. The radius of the disc is proportional to the wavelength of the light but inversely proportional to the pupil size.
 

9. The following tests are used in testing the vision of pre-verbal 
    children:

a. Log MAR

b. STYCAR

c. Catford drum

d. Cardiff card

e. Sheridan-Gardiner tests
 

Answer
a.F   b.T   c.T   d.T   e.T
 

10. Regarding visual acuity:

a. it can be represented a reciprocal of the minimum 
    angle of resolution

b. it varies with the region of the retina

c. it is affected by general illumination

d. it is affected by the colour of the test objects

e. it is affected by the time of exposure
 

Answer
a.T   b.T   c.T   d.T   e.T

11. Pinhole:

a. if less than 1mm diameter impairs the image quality

b. abolishes the need for the eye to focus

c. increases the depth of focus

d. increases the depth of field

e. improves ametropia of less than 6 D
 

Answer
a.T   b.T   c.T   d.T   e.F
Pinhole allows a single ray of ray to enter the eye and therefore abolishes the need for focusing. It can improves ametropia up to 4D. If too small ie. less than 1mm in
diameter, the image quality is impaired due to diffraction.
Pinhole by reducing the effective pupil diameter increases both the depth of focus and depth. The depth of focus which is the distance in front and behind the focal point or retinal over which the image may be 
focused without causing reducing in sharpness beyond a 
certain tolerable amount. The depth of filed is the distance
over which an object may be moved without causing a sharpness reduction beyond a certain tolerable amount. 
Both are inversely proportional to the diameter of the pupil.

12. Contrast sensitivity:

a. measures the eye sensitivity to light

b. is inversely proportional to contrast

c. can be measured with Snellen's chart

d. can be measured with VISTECH

e. may be reduced following LASIK 
 

Answer
a.F    b.T   c.F   d.T   e.T
 Contrast sensitivity tests the ability of the eye to detect luminance contrast. It is the reciprocal of the minimum perceptible contrast. It gives an evaluation of the detection of objects usually sinusoidal gratings on a chart or generated on an oscilloscope display of varying spatial frequencies an d of variable contrast. The letters on Snellen's chart are of high contrast and not useful for contrast sensitivity testing. VISTECH can be used to measured contrast sensitivity, it consists of a chart containing five horizontal rows, each with nine circular patches of sinusoidal gratings. The gratings are either vertical or 15 degrees to the right or to the left.
 

13. The following are true about birefringence:

a. they have two refractive indices

b. they split a light into two polarized lights

c. polarimetry uses the birefringence of the nerve fibre 
    layer to quantitate its thickness indirectly

d. it is used in pleoptics to produce Haidinger's brushes

e. amyloid when stained with Congo red produces 
    birefringence.

Answer
a.T   b.T    c.T    d.F   e.T
Substance with birefringence properties will split incident unpolarised light into two polarized beams travelling different directions. Therefore, they are said to have two different refractive indices.
Polarimetry uses the birefringence of the NFL (nerve fibre layer) to quantitate its thickness indirectly. The change in the polarization of light as it passes through the NFL, or “retardation,” is measured and linearly correlated to the NFL thickness.
Pleopitcs used to produce Haidinger's brushes requires the use of polarized light.
Amyloid such as those seen in lattice dystrophy has birefringence property when stained with Congo red.

14. In stereoscopic vision testing:

a. corresponding retinal areas in both eyes are stimulated

b. the grading is based on the least horizontal disparity of 
    retinal image that evokes depth perception

c. in normal person, the value is about 60 seconds of arc 
   or better

d. amblyopia is unlikely if the stereoacuity is better than 250
    seconds of arc

e. the TNO test can give stereoacuity from 450 to 15 
    degrees of arc
 

Answer
a. F   b.T   c.T   d.T    e.T
In stereoscopic vision, disparate retinal elements within Panum's fusional areas in the two eyes are stimulated giving rise to depth perception.
The grading is based on the least horizontal disparity of retinal image that evokes depth perception. The unit is seconds of arc.
The normal individual has a stereoacuity of 60 seconds of arc. Amblyopia is unlikely if the stereoacuity is better than 250 seconds of arc.
The various tests for stereoscopic vision include:
Titmus test: 3000 to 40 degrees of arc
Frisby test: 600 to 15 degrees of arc
TNO test: 450 to 15 degrees of arc
Lang stereotest: 1200 to 550 degrees of arc

15. The following refers to the amount of light arriving at a given point:

a. illuminance

b. brightness

c. shininess

d. irradiance

e. radiance
 

Answer
a. T   b.F   c.F   d.T   e.F
Illuminance and irradiance are terms used to refer to the
amount of light arriving at a given point. Radiance refers
to the amount of light leaving a certain point.

 

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