Slit Lamps

Question 1

Explain parallelepiped advantages/disadvantages

Answer 1

Ad:
Scans corneal layers (endo/epi) most prone to compromise, quick effective (CL AF), mag allows small lesion detection

Dis:
difficult (cornea curved/varied thickness)
no info for lesion depth (abrasions/FBs)

Question 2

Explain the advantages/disadvantages of corneal section

Answer 2

Ad: detailed depth of layers/lesions
Dis: poor scanning

Question 3

Explain the advantages/disadvantages of anterior vitreous

Answer 3

Ad: detects ret.det Shafers
Dis: dilate older px with ret det signs

Question 4

Explain the advantages/disadvantages of specular reflection (endothelium)

Answer 4

Ad: checking polymorph/megathism in CL A/Care, cheaper than microscope
Dis: small portion checked at PI, needs good skill/control

Question 5

Explain the advantages/disadvantages of speculative reflection (lens)

Answer 5

Ad: checks lens deposits, PEX syndrome (glaucoma)
Dis: surface only not cataracts within

Question 6

Explain the advantages/disadvantages of iris retro illumination

Answer 6

Ad: examines low contrast features (keratic precipitates), checks limbal BVs for NV (CL AC)
Dis: dark iris reflects less light, long to check whole limbus

Question 7

Explain the advantages/disadvantages of retro illumination (fundus)

Answer 7

Ad: detects opacities easily with good glow, pigment dispersion syndrome (iris disorders), easy on dilated px

Dis: hard on small pupils/dark fundus, no info on opacity depth

Question 8

Explain conical beam and it’s advantages/disadvantages

Answer 8

Checks aq flare of AC, hypopyon/hyphaema

Ad: detects inf. proteins (fibrinogen/interleukin), in inner eye, rule out uveitis/post-cat surgery inflammation
Dis: difficult, subtles signs influenced by glare/room light

Question 9

Explain sclerotic scatter and it’s advantages/disadvantages

Answer 9

TIR principle checks for corneal opacities

Ad: screening tool, oedema, locates FB, ulcers, infiltrates, px comfortable
Dis: low mag little detail, PP can detect FBs takes less time

Question 10

Explain van Hericks and it’s advantages/disadvantages

Answer 10

Estimates ACD/ACA

Ad: ensures angle wide enough to dilate
Dis: only estimate, cornea thickness variable between px, should be perpendicular not 60 degrees

Question 11

Explain N Smiths technique and it’s advantages/disadvantages

Answer 11

Measures ACD not angle

Ad: accurate to +/-0.33mm
Dis: no angle info, difficult to set up, some lamps don’t have a adequate slit height

Question 12

Explain the use of fluorescein instillation

Answer 12

CSF (Corneal surface fluorescence)
Non-toxic, px comfortable, stains apoptosis

In cell through glycocalyx layer to para cellular space (via dormant tight junctions) continues into deeper layers/spaces

Question 13

Explain fluorescein filters and excitation

Answer 13

Blue Photons (495nm) excite FL molecules, returns to ground state emitting green (520nm)

Excitation filter maximises excitation
Barrier filter select for emitted light of FL

Question 14

Which 2 factors affect fluorescence?

Answer 14

Tear pH (higher gives better emission)
Amount FL instilled (quenching, too much ~ subtle corneal damage)

Question 15

Which other filters can protect the px?

Answer 15

Heat absorber (prevent IR damage)
UV (damage)
Red-Free
Neutral Density (reduces light equally across spectrum)
Polarising (reduces reflections/scatter in 1 plane)

Question 16

Explain tear break up time (TBUT) and it’s advantages/disadvantages

Answer 16

Instil FL (floret), blue excite filter (maximum beam), yellow barrier filter

Px blinks, eyes open as long as can, (dark streaks before 10 secs ~ unstable tear film)