Chapter 14: Instruments C Flashcards
What are 6 methods of illumination with the slit lamp?
- Direct focal illumination
- Diffuse illumination
- Lateral illumination
- Retroillumination
- Specular reflection
- Sclerotic scatter
What type of slit lamp illumination is the most generally useful for illuminating the eye?
direct focal illumination - slit beam accurately focused upon that part of the eye under inspection
What is diffuse illumination with the slit lamp?
beam of light thrown slightly out of focus across the structure being examined so that a large area is diffusely illuminated
What part of the eye is diffuse illumination with the slit lamp useful for?
anterior capsule of the lens
What does lateral illumination with the slit lamp involve?
illuminating the structure by light which is refleced from tissue just to one side of it e.g. directed at margin of pupil, illuminates outer rim of sphincter muscle
What is retroillumination with the slit lamp?
method of examining part of the eye by light reflected from a structure behind it - structure behind is used as a mirror
What is a key example of a use of retroillumination with the slit lamp?
areas of iris atrophy identified by light which is reflected from the choroid
Where should the illuminating column of the slit lamp be moved to to perform retroillumination?
should be brought to lie between the objective lenses of the microscope so the illuminating and viewing systems are co-axial
What is specular reflection with a slit lamp?
examining rays of light reflected from a mirror-like surface (corneal surfaces and anterior lens capsule)
Where is the patient’s gaze directed in specular reflection with the slit lamp?
to bisect the angle between axis of illumination and that of the microscope
What 2 structures can be examined with specular reflection?
- corneal surfaces including corneal endothelium
- anterior lens capsule
What is sclerotic scatter?
the slit beam and the binoculars are dissociated so that the limbal sclera is illuminated, while the binoculars are centered on the cornea. the whole limbus glows and the light from the beam is reflected back and forth between the two internal limiting surfaces of the cornea and is scattered centrifugally all around the cornea
If the slit beam is directed to the limbus at 9 o clock to achieve sclerotic scatter, where will the maximum glow be?
3 o’clock
What are 2 types of slit lamp filters which can be used?
- blue cobalt filter
- blue and green (red-free) filters
What is the blue cobalt filter used for with the slit lamp?
applanation tonometry
What are th eblue and green (red free) filters useful for with the slit lamp? 2 reasons
- examination of the vitreous
- to create dark fundus background to easier detect structures in the vitreous e.g. vitreous cortex in PVD
Why are blue and green (red-free) filters useful for examining the vitreous?
scattering of light is greatest when the incident light is of short (blue) wavelength - visibility of vitreous depends on light being scattered
What is the furthest back in the eye that can be seen with the slit lamp on its own?
anterior third of the vitreous
Why is it impossible to see further than the anterior third of the vitreous with the slit lamp alone?
refractive power or cornea and lens renders light emerging from deeper points of the eye parallel so no image formed within focal range of hte slit lamp microscope
How can the fundus be viewed with a slit lamp?
using additional lens to overcome the refractive power of the eye; improved if light reflected from cornea doesn’t enter slit lamp (no overlap at the cornea of illuminating and viewing systems)
What can be done in order to avoid reflection of light from cornea entering slit lamp microscope when performing fundal examination?
if there is no overlap at cornea of illuminating and viewing systems - tilt illumination column so axis is below that of viewing system
What are 4 devices which can be used to visualise the fundus with the slit lamp microscope?
- Hruby lens
- Fundus-viewing contact lens
- 90D and 78D lenses
- Panfundoscope contact lens
What is the Hruby lens used for?
examination of fundus and posterior vitreous with slit lamp
What is the Hruby lens used for?
examination of fundus and posterior vitreous with slit lamp
What is the Hruby lens and how does it work?
- powerful plano-concave lens, -58.6 D
- placed with concave surface towards eye
- held immediately in front of eye, forms virtual, erect and diminished image of illuminated retina
What 2 qualities are met to give the best image of the fundus and posterior vitreous with the Hruby lens?
- lens held near eye
- retinal image found in pupillary plane
What can be examined with the fundus viewing contact lens?
posterior vitreous and posterior pole of fundus
What type of lens is the fundus viewing contact lens?
plano-concave with higher refractive index than eye
What 2 things may be used as a fundus-viewing contact lens?
- central zone of gonioscopy lens
- central zone of three-mirror contact lens