3.1.2 Uses a slit lamp to examine the external eye and related structures.

Low magnification

x6-x10

• Lids

• Bulbar conjunctiva

• Cornea / limbus

• Tears / tear film

• Anterior chamber / iris

• Crystalline lens

Medium magnification

x20-x25

• Epithelium of cornea

• Stroma of cornea

• Endothelium of cornea

• Lens fits / surface of contact lenses

and movement on blink

High magnification

x30-x40

• Epithelium: vacuoles, microcysts, dystrophies

• Stroma: striae and folds

• Endothelium: polymegethism, blebs, dystrophies

Diffuse illumination

Allows overall examination of the eye and adnexa

Direct focal illumination

Optic section

Gives cross section of the cornea (illumination has to be perpendicular to cornea)

Parallel Piped

Width of 1mm. Used for looking at corneal nerve fibres and punctate keratitis

Conical Beam

Must be carried out in a very dark room o see if there is any light scatter back at us which shows the inflammatory cell, if any, in the anterior chamber

Observed at 45-60 degrees allowing us to observe all areas

In-direct illumination

Used for epithelial vesicles and erosions. There are two types of systems:

Coupled - when illumination and observation system swing around the same pivot point

De-coupled - when the illumination system is moved to the side therefore it no longer meets the optimal focus of the observation system

Retro-illumination

Light bounces off the iris or fundus to back illuminate the cornea (Requires de-coupled system)

Used for observing microcysts, vacuoles, cataracts, contact lens deposits

Specular Reflection

Angle of incidence of illumination is equal to angle of observation

Purkinjie image 1 - front surface of cornea

Purkinjie image 2 - endothelium, where there is a change of R.index from cornea to aqueous

Purkinjie image 3 - front surface of the lens

Purkinjie image 4 - back surface of crystalline lens

Medium to high magnification

Focus on area of interest and swing illumination beam until specular reflection achieved

Only visible through one eyepiece at a time

Tangential

Illumination at right angles to structure of interest

Low magnification

Wide angle beam but narrow

Used for iris freckles, general integrity of cornea and iris

Sclerotic scatter

Illumination slit located on limbus

You see halo of light in darkened room

Observation system de-coupled

Low magnification

Used for corneal opacities, corneal swelling, foreign bodies

Fluorescein examination

Assess staining of cornea & conjunctiva

Assess tear break up time

Assess tear meniscus height

Use Wratten filter to enhance image

Van Herick’s Technique

Low magnification Grd 4 - 1:1 open

Optic section with higher of 3-4mm Grd 3 - 1:2

60 degrees angle to observation Grd 2 - 1:4

Comparing width of cornea to anterior chamber Grd 1 - 1:<4

Grd 0 - closed

Conduct assessment also on the nasal side, if patient’s nose gets in the way lock the slit lamp at 60 degrees and move both systems approximately 5-10 degrees away from the nose, but ENSURE patient looks directly at the microscope before assessing the angle.