3.1.2: Use SL to examine external eye & related structures

Question 1

What are the uses for low mag, medium mag and high mag?

Answer 1

o Low magnification (6x – 10x)
➢ General: Lids, Bulbar conjunctiva, Cornea, Limbus, Tears, Anterior chamber, Iris, Lens
o Medium magnification (16x – 25x)
➢ Structures: Epithelium, Stroma, Endothelium, Lens fit and surface
o High magnification (30x – 40x)
➢ Details: Epithelium (Vacuole, Microcyst), Stroma (Straie, Folds), Endothelium (Polymegathism, Dystrophy)

Question 2

Describe the slit lamp beam/light filters?

Answer 2

Cobalt blue: Used with fluorescein dye during assessment of dry eyes, contact lenses, and Goldmann applanation tonometry
Neutral density: Reduces the brightness of the illumination and is complemented by the rheostat on the instrument.
Yellow/Wratten 12: Can be used in addition to the Cobalt blue filter to enhance contrast.
Red free (green): Enhances the contrast of blood vessels on the corneas of contact lens wearers and
haemorrhages seen under the conjunctiva
Diffuser: Generally used with a wide beam and low magnification with non-directional illumination for gross assessment of the eye.

Question 3

Describe diffuse illumination?

Answer 3

• Angle: 45°.
• Widest beam.
• Diffusing filter.
• Magnification: 10-16x
• Illumination: medium to high.
  Uses: eyelids, lashes, conjunctiva, sclera, pattern of redness, iris, pupil, gross pathology, and media opacities

Question 4

Describe parallelepiped?

Answer 4

• Angle: 45 °
• Slit: 1-2mm in width
• Filter: None
• Magnification: 16-25x
• Illumination: medium
  Uses: * Detect and examine corneal structures and defects
• Higher magnification preferred to evaluate both depth and extent of corneal scarring or foreign bodies.
• View corneal nerve fibres, punctate keratitis

Question 5

Describe optic section?

Answer 5

• Angle: 45 °
• Slit: width minimum 0.01mm
• Filter: no filter
• Magnification: 25-40x
• Illumination: medium
  Uses:
• Used to localise: Nerve fibres, Blood vessels, Infiltrates, Cataracts, AC depth.
• To discover thickening, thinning, and distortions in the corneal contour.
• To determine the depth of foreign bodies or opacities in the corneal substance. (a % of the total corneal thickness)
• To see a wide slice of stroma. (The angle between the microscope and illuminating arm can be increased.)

Question 6

Describe conical beam?

Answer 6

➢ Narrow and short beam
➢ Medium magnification
➢ 45-60 degree angle
➢ Must be in darkened room pupil acts as a dark background
➢ Use – inflammatory cells and flare in anterior chamber

Question 7

Describe specular reflection?

Answer 7

➢ Angle of incidence of illumination is equal to angle of observation
➢ Bright reflection (Purkinje images) seen from corneal surface (tears) acting as a mirror
➢ Medium to high magnification (16-40x)
➢ Illumination: med to max
➢ Slit width 4mm
➢ Only visible through one eye piece at a time
➢ Swing illumination arm till reflection achieved reduce angle for deeper structures
Uses:
* Tear film debris and flow, Endothelium, Crystalline lens (orange peel)
* To visualize the integrity of the tear film (lipid layer), corneal and lens surfaces
* To visualize the endothelium
1. Start with lower magnification (10X to 16X).
2. Direct a relatively narrow beam onto the cornea
3. Switch to the highest magnification available
-> Endothelium is best viewed using only one ocular.
* Under specular reflection anterior corneal surface appears as white uniform surface and corneal endothelium takes on a mosaic pattern.

Question 8

Describe indirect illumination?

Answer 8

➢ Same as direct, but looking to the side of the light beam
➢ Direct beam may bleach defects from view
➢ Should decouple to focus observation system to side of the direct beam
➢ Uses – Epithelial vesicles, erosions, Iris pathology, Iris sphincter, Limbal vessels

Question 9

Describe retro illumination?

Answer 9

➢ Use the iris or fundus to back illuminate the cornea
➢ Moderate wide beam
➢ Decoupled
➢ Medium to high magnification ( 10-16x)
➢ Use – Microcysts, Vacuoles, Lens opacities (PSCC, water cleft), CL deposits, Vascularisation

Question 10

Describe sclerotic scatter?

Answer 10

➢ Illumination slit located on limbus, observation decoupled and focused on cornea
➢ Low magnification
➢ Total internal reflection, Halo of light in darkened room if cornea healthy
➢ Use – Corneal opacities, swelling or foreign body in cornea

Question 11

Describe Van Herick’s?

Answer 11

• Angle: 60°
• Slit: Optic section
• Filter: No filter
• Magnification: Medium (10 or 16x)
• Illumination: Medium to maximum
• Comparing width of cornea to anterior chamber
  Grading:
  Grade 4 open ACA 1:1 ratio
  Grade 3 open ACA 1:0.5 ratio
  Grade 2 narrow ACA 1:0.25 ratio
  Grade 1 risky narrow ACA less than 1:0.25
  Grade 0 closed ACA cornea “sits” on iris

Question 12

What is involved in a slit lamp examination?

Answer 12

o Fluorescein assessment
➢ Assess staining of cornea and conjunctiva
➢ Assess tear break up time
➢ Assess tear meniscus height
➢ Use yellow (Wratten) filter over observation to enhance image
o Lid eversion
➢ Assess tarsal conjunctiva under white/blue light (with fluorescein)
o Van Herick’s Technique
➢ Comparing width of cornea to anterior chamber
o Tonometry
➢ Goldmann applanation tonometry with aid of flourescein
o Gonioscopy
➢ Gonioscopy lens using mirrors to directly view anterior chamber
o Pachymetry
➢ Measurement of corneal thickness and regularity
o Fundoscopy
o Lens fitting and assessment