What is fluorescence?
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The property of a molecule to spontaneously emit light of a longer wavelength when stimulated by light of a shorter wavelength.
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What is fluorescence?
The property of a molecule to spontaneously emit light of a longer wavelength when stimulated by light of a shorter wavelength.
What happens to fluorescein sodium when excited by blue light?
It emits yellow-green light.
What do the terms 'limit of resolution' and 'resolving power' refer to?
The smallest angle of separation between two points that allows the formation of two discernible images by an optical system.
When two Airy discs are separated so that the center of one falls on the first dark ring of the other.
What type of color vision defect does the Ishihara test specifically target?
Congenital red-green defects.
They see only a random pattern of spots or incorrect numbers.
How does a fluorescein camera illuminate the fundus?
By passing white light through a blue 'excitation' filter.
What does the Lanthony New Colour Test evaluate and who is it used for?
Hue discrimination. only used by children
What is used to measure vernier visual acuity?
An offset square wave grating.
What does the yellow-green 'barrier' filter in the camera do?
It blocks blue light and exposes the camera film only to yellow-green light from fluorescein.
What wavelengths are retinal photoreceptors sensitive to in the near ultraviolet?
Between 400 nm and 350 nm.
What is the discernible offset for vernier visual acuity?
3–5 seconds of arc.
What is the bright central zone in a circular diffraction pattern called?
The Airy disc.
What is phase difference?
The fraction of a cycle or wavelength by which one wave leads another.
What effect does UV radiation have on aphakic or pseudophakic eyes?
It can cause the sensation of blue or violet colors.
What does a person with 6/12 vision indicate?
They can identify letters on the '12' line from 6 m.
At what distance is near visual acuity usually tested?
25–33 cm.
What are visual evoked potentials?
Electrical responses generated in the occipital cortex by visual stimulation of the eye.
What phenomenon occurs due to overlap in the spectral transmission of excitation and barrier filters in fluorescein angiography?
Pseudofluorescence.
What does the British N system use to specify letter size?
The typesetters' point system.
What types of stimuli are used in visual evoked potential testing?
A black and white square wave grating or a chequerboard pattern.
What visual acuity can young adults often achieve?
6/4 acuity.
How is one point defined in the British N system?
1/72 inch.
What is an optotype?
A symbol whose identification corresponds to a certain level of visual acuity.
What does cone dystrophy and Stargardt's disease cause?
predominantly red–green defect
What happens when two waves of light are in phase?
They produce constructive interference, resulting in a summation of the two waves.
What is destructive interference?
It occurs when two waves of equal amplitude are out of phase by half a cycle, canceling each other out.
What is the initial effect of glaucoma on colour vision?
It predominantly causes a blue–yellow deficit.
What is the absorption and emission wavelength of Indocyanine Green (ICG) dye?
Absorbs at 805 nm and emits at 835 nm.
What is the Kay's pictures test?
A test using pictures of objects like a cat, train, or house for visual acuity assessment.
Why can fluorescence of the choroidal circulation be observed after ICG administration?
Because the retinal pigment epithelium does not absorb the wavelengths emitted by ICG.
Where does destructive interference occur within the eye?
Within the stroma of the cornea.
In wave motion, how do the particles of the medium move?
They vibrate at right angles to the direction of the wave.
What letters are used in the STYCAR letter tests for children?
H, O, T, V, and X.
What percentage of 805 nm radiation absorbed by ICG is emitted at 835 nm?
4%.
What is the purpose of potential visual acuity testing?
To assess the potential visual acuity of eyes where the macula cannot be seen.
How do collagen bundles in the cornea contribute to light interference?
They are spaced such that any light deviated by them is eliminated by destructive interference.
What type of defects does acquired retinal disease typically cause?
Blue–yellow defects.
What advantage does ICG angiography have over fluorescein angiography?
It can delineate occult choroidal neovascularisation not visible with fluorescein.
How has ICG been used in relation to vascular lesions?
To photosensitise vascular lesions for diode laser photocoagulation.
How do low reflection coatings work?
They consist of a thin layer of transparent material that causes light reflected from the superficial and deep surfaces to eliminate each other by destructive interference.
How are the colours in the FM hue 100 test arranged?
In a row with reference colours at each end and intervening discs in order of closest colour match.
84 coloured discs.
What should be done as soon as a child is old enough for visual testing?
Tests requiring matching should replace those based on behavioral responses.
What does CSM stand for in visual examination?
Central, steady, and maintained fixation with either eye.
What indicates poor visual acuity in a child?
A strong preference for one eye, indicated by aversive responses to occlusion, squint, nystagmus, roving gaze, and eye poking.
When does visually directed reaching typically develop?
Between two and five months of age.
What visual acuity is suggested by a 15-month-old child picking up a tiny colored sweet?
Near visual acuity equivalent to 6/24 or better.
What does the Catford drum test measure?
Visual acuities ranging from 6/6 to 2/60 when viewed from 60 cm.
Comprises a white cylinder marked with black dots of increasing size corresponding to visual acuities
What is a limitation of the Catford drum test?
It overestimates acuity due to the moving target and short working distance.
What does the STYCAR test involve?
Rolling ten white polystyrene spheres across a contrasting floor to assess visual tracking.
How can preferential looking be used in visual acuity assessment?
By observing infants turning their head or eyes towards a patterned target rather than a uniform one.
What is the D-15 test?
Uses colours from all parts of the spectrum which must be arranged in order from a single reference colour.
The test does not distinguish mild colour defects, but for most purposes those passing the test are unlikely to have problems with hue discrimination.
