Chua 3 Flashcards
What is field of view in direct vs indirect ophthalmoscope?
Magnification?
Direct 6 degrees
Indirect 25 degrees
Direct 15x
Indirect 13D - 5x, 20D - 3x (60D/power of lens)
What affects field of view in indirect ophthalmoscopy?
Size of observer’s pupil
Diameter of condensing lens - larger = larger field of view
Power of condensing lens - stronger lens = larger field of view
Size of patient’s pupil affects field of illumination
What lenses are used to reduce aberration in indirect?
Aspheric lenses
Where is the image formed in indirect?
AT/near second principal focus of condensing lens
How does laser spot magnification change with strength of lens?
Laser spot magnification increases with stronger lenses
What happens to image size in emmetrope / myope / hypermetrope when lens moved towards patient eye
Emmetrope - no change in image size
Myope - larger image size as lens moved away from patient eye
Hypermetrope - smaller image size as lens is moved away from patients eye
Where is image located in indirect of myopic eye? Hypermetropic?
Myopic - within second principal focus of condensing lens
Hypermetropic - outside of second principal focus of condensing lens
What can with movement on retinoscopy indicate? Against movement?
Against is always myopia
With can be myopia if myopia is less than dioptric value of working distance (working distance needs to be subtracted)
When is the neutral point reached?
When paitent’s far point conincides with the observer’s nodal pointW
What mirror systems are used for retinoscopty?
Plane and CONCAVE mirror
What does the keratometer do to negate ocular movement?
Double central image
What are magnification / field of view / laser spot magnification of 20D, 28D, 78D, 90D
Magnification, decreases with stronger lens
20D - 2,97
28D - 2.16
78D - 0.87
90D - 0.72
Superfield - 0.72
Field of view
20D - 46
28D - 55
78D - 73 (larger diameter than 90D)
90D - 69
Superfield 120
Laser spot increases with increasing power
How do con helmholz keratometer and javal schiotz keratometer differ
vOn-helmhOltz - fixed Object size, image size adjusted to measure the corneal curvature
Uses parallel glass plates X and Y to double the image to overcome eye movmeents
Angle of inclination varied by observer until edges of two images touch
javal schIotz - fixed image size - object size varied to measure corneal cruvatre
Consists of pair of mires (small latterns with coloured windo a and B mounted on curved side arms
Doubling of image through Wollaston prism in viewing telescope
Space between mires is object size
Each step of mire is equivalent to 1D
What is a slit lamp made up of?
Low powered binocular compound microscope with lighting systema nd microscope on common focal plant
Prisms to invert image and shorten
How does the slit lamp adjust magnification
Galilean telescopes of different powers incorportated into slit lamp
What is diffuse illumination
Full height, broad, low brightness, slightly out of focus beam onto ocular surface from side
TO inspect anterior capsule
What is direct focal illumination
Direct oblique medial beam accurately focussed on part under inspection
Specular reflection? What is it good for?
Gaze directed to bisect angle between axis of illumination and observation
Corneal endothelium and anterior lens capsule can be examined this way
Sclerotic scatter
Slit beam is directed onto the limbus from side, whole limbal area glows
Decentration of slit lamp
Light scattered all around cornea
Retro illumination
Iris atrophy
Light reflected from choroid seen
Lateral illumination
LIght directed to the side of lesion - some of light enters the lesion causing it to glow internally
What filter for examining vitreous
Blue/green
Low wavelength light scattered more
Less light reflected from fundus
What is the Hruby lens? Power? Image?
Plano concave lens -58.6 power
Held with concave surface towards eye
Virtual erect diminished image
Image formed within the eye
Power of eye, cornea, lens
Power of eye +58.6
Cornea 43.1
LEns 19.1 (15 in situ)
