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What is meant by isocentric?
Lamp arm swings on same axis that microscope swings
What is meant by parfocal?
microscope is focused on the same plane that the light beam is focused on
What are both the light beam and microscope focused on and how is this advantageous?
the axis of rotation, can move both together on the baseplate
what do these filters do: red free, colbalt blue, neutral density, yellow, diffuser?
- 1. looks green- enhances view of bv and haemorrhages
- 2. colbalt blue- enhances fluorescein due
- 3. neustral density- decreases maximum brightness for photosensitive patients
- 4. diffuser- general overall observations of the eye and adnexa
What is direct illumination and what is it used to see?
- Illuminating and viewing system are sharply focused on the same area
- travels through transparent tissue
What are the characteristics of an optic section?
- very narrow
- beam is thinnest at the focal plane
What is the use of an optic section?
- depth determination- cornea, anterior chamber
- angle estimation
- lens depth/location/layers
What is the set up for an optic section of the cornea?
- illumination 30- 45 deg away from microscope (wide angle)
- low mag
How is an optic section of the lens carried out?
- SL focused on lens
- best done after dilation
- dilated pupil use wide angle 45
- non dilated pupil/elderly- 15 deg
What can be seen with an optic section of the lens?
- y sutures
- lens fibre layers
What is a parallelipiped?
- low-mod mag
- 3D box of tissue
What is a conical beam?
- mod-high mag
- totally dark room
What can be seen with a conical beam?
- focused in the ant chamber (between cornea and iris)
- swing lamp around to see wbc, fribrin, flares or floating cells
What is tangential illumination?
- angle between microscop and light beam is very large
- narrowish beam
- tangential to tissue in question
- purpose is to highlight elevations and depressions
- casts shadows
- enhance surface texture
What is specular reflection?
- Based on the principle of snell's law angle of incident ray= angle of reflected ray
- 40-60 deg
- high mag
What is specular reflection used to see?
- endothelial cells of the corneal endothelium
- cells are high reflective
- see a honeycomb pattern
- see holes- whether pits or volcanoes
What is the 'normal' variation of the size of endo cells of the cornea?
What are the conditions needed to see the specular reflection of the anterior lens?
lens needs to be perpendicular to microscope
What is indirect illumination?
Light is bounced beyond point of original direct impact to illuminate object of regard from the side or behind
What is proximal viewing?
- moderate beam directed adjacent to the area of interest, the absorption and scattering of light around and behind the abnormality will increase its contrast
- look next to where beam is illuminated
- 45 deg
How is sclerotic scatter carried out?
- focus microscope onto central cornea and lock
- move light beam to limbus until a halo can be seen
- scan cornea for areas of light scatter
What is seen in a healthy/an unhealthy cornea with sclerotic scatter?
- shows distribution changes of cornea and corneal abnormalities
- halo of light at other limbus- nothing disturbs the passage of light and is therefore not visible
- abnormality present- light is visible by relfecting, refracting and scattering part of light towards SL
What is retro illumination?
light reflected off deeper textured structure scatters widely and provides a bright background against some abnormalities within the anterior structures
What is retroillumination used to see?
- opaque/light objects- appear dark against bright bg
- objects that scatter light- appear lighter than bg
What is direct retroillumination?
- moderate size beam
- tangential/wide angle ~60 deg
- View where the bg is the brightest
- may need offset at higher mag
What is indirect retroillumination?
- decentering the slit beam further from its iso-centric position so the intended area of cornea is seen against a dark bg
- light scattered by adjacent illuminated iris is sufficient
look at the merge zone between light and dark
What is retroillumination off the fundus?
- by directly illuminating the RPE, a bright bg is created to secondarily illuminate or silhouette abnormalities in the anterior vitreous, lens, chamber and cornea
- used mainly to see iris disorders and cataracts
What is the setup for fundus retro?
- dilated pupil
- near coaxial placement- so that the incident and reflected light can both pass through the pupil
What is a Van Herick's test?
- A test that provides an estimationg of the anterior chamber depth
- Used as a safety precaution against inducing acute angle glaucoma during dilation
Estimate of anterior chamber depth in older hyperopic px?
- small due to growth of lens
- liable to closure
Estimate of ant cham depth in myopic px?
What is the set up for Van Herick's test?
- mag 16X
- optic section
- microscope and light beam 30 deg from fixation on either side
- how many cornea's fit into the aqueous space?
What is the criterion for Van Herick's test?
Why is the 12 o'clock limbus NOT measured with Van Herick's test?
scleral tissue travels a long way through the cornea
What is the recorded result of a Van Herick's test?
- anterior chamber/cornea