omi term 2 Gonioscopy and topographic imaging Flashcards
Wha is gonioscopy
method of examining the anterior angle of the eye and the angle allows us to see where outflow of aqueous humour occurs
wha does drainage of aqueous humour allow
helps maintain sensible level of pressure in eye
too low pressure is hypotension which means part of eye becomes damaged and leads to swelling of cornea
too high pressure is hypertension meaning damge within eye and loss of nerve fibre cells in optic nerve head leading to glaucoma
its important to see the angle is open as it should be as if it is closed pressure will build up withing eye leading to serious eye issues
total internal reflection
light tha travels at a medium with high refractive index to one with a lower refractive index light travels away from the normal
after critical angle total internal reflection occurs
viewing anterior angle requres an angle beyond the critical so TIR occurs a tear film/air boundary
types of goniolens
direct, provides direct view of an angle, curve of lens refracts light ray at lens-air interface (koeppe goniolens)
indirect- provides mirror image of opposite angle (goldmann, zeiss goniolens)
direct gonioscopy strenghts and weaknesses
strenghts- paronamic view, detialed examination, can be used in sedated patients
weakness- time consuming, corneal light reflexes cause issues
indirect gonioscopy
strenghs- easy to use, less time consuming
weakness- can only view one section at time, mirror is seen
3 mirror lens has 4 possible viewpoints (goldmann)
four mirror lens has two possible viewpoints (topcon)
indirect gonioscopy-lenses
3 mirror lens has 4 viewpoints by using 3 diff mirrors and a lens
lens- view the posterior pole of the eye
trapezoid mirror (73 degrees)- view equatorial section
rectangular mirror (67 degrees) view ora serrata
d shaped mirror (59 mirror) view anterior angle
4 mirror lens
lens-view posterior pole of eye
d shaped mirror (59 degrees)-view anterior angle
types of images seen
cornea shwalbes lines trabecular meshwork non pigmented trabecular network pigmented scleral spur ciliary body band iris
topographic imaging
art of graphic delineation in detail using maps or charts of natural or man made features of a place or region in a way to show their relative positions and elevation
lines closer together represent steeper incline
for certain parts of eye useful to know shape or curvature
cornea most powerful refractive component and if it is misshaped it could have implications for sight
eg: keratoconus-cone shaped cornea
use of topographic imaging
diagnosis- keratoconus,astigmatism,corneal scarring
screening-check eligibility for refractive surgery
longitudnal monitoring- monitor progression of condition over time
contact lens fitting- measure shape of cornea to fit best contact lens
topographic techniques
OCT-anterior segment
keratoscopy/placido disc
only central few mm of cornea considered as spherical
human cornea complex shape resembling eclipse
shape of cornea quanitfied by shining placido disc on it and assessing shape of reflected image
medmont corneal topographer
can measure from limbus to limbus which means it has more coverage than other techniques
