1 Direct Diffuse illumination is typically the first method of illumination used to determine general ocular health.

Lighting is arranged so that the eye being viewed is illuminated from many different directions. It is used for:

•General observation of the eye prior and post contact lens fitting •Observation of the pre-corneal film. •Depth of a corneal scar. •Depth of an embedded foreign body. •Detect changes in corneal thickness. •Lids, eyelashes , caruncle are easily observed with this method of illumination •The entire extent of a corneal scar can be observed •Neovascularization •Infiltration •Edema

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Uses of Direct Diffuse Illumination

•Identify the tear layer •Discover thinning and thickening of the corneal surface •The depth of foreign bodies •To examine the crystalline lens •Estimate the depth of the anterior chamber

3 The diagrams depict the three different light source techniques: •Optic Section •Parallel Piped •Conical Beam

4 Using Direct Focal Illumination with an Optic Section technique the optician can view the layers of the cornea.

These diagrams show the layers of the cornea.

1. The bright outer layer is the tear layer. 2. The dark line right after the bright layer is epithelium 3. Bowmans layer bright line 4. The stroma as the main body 5. The dark line at the end is the endothelium

5 Parallelepiped is usually a beam from 5 – 7 mm.

1. To give a wide view of the stroma 2. To determine irregularities on the surface of the cornea 3. To make general observations of the cornea surface such as scars, abrasions and blood vessels 4. To determine the fitting of a rigid lens

6 A conical beam is a small round circle. This is achieved by adjusting the vertical to a minimum and adjusting the horizontal to a minimum.

Function: •To observe aqueous flare and cells •To observe debris floating in the anterior chamber •Punctum excise

7 Method:

A narrow light beam is projected almost parallel along the structure to be observed. Elevated structures are visible by shadowing Illumination angle 70-90 degrees.

Uses of Tangential Illumination:

•Striae lines and nerve fibres in the cornea •With a blue filter to observe Fleisher’s ring in Keratoconus •Pathology of the Iris •Floaters in the anterior chamber

8 Definition The oculars and light source are positioned that when light reflects from the corneal surface it passes through one of the oculars. The angle of incidence is equal to the angle of reflection.

9 With Indirect Illumination the beam of light is focussed next to the ocular tissue that is to be observed.

The lamp house is focused on a structure located adjacent to the structure being observed.

Valuable in studying the Iris Observation of the corneal epi thelium.

10 This method of illumination relies on the principle of total internal reflection creating a halo like effect around the limbus. The eyepieces are not used. The surface of the cornea is viewed with the naked eye.

The beam of light shines on the limbus and scatters off the sclera as demonstrated in this diagram.

The soft indirect light highlights very subtle corneal changes such as corneal scarring, corneal opacities and corneal edema To observe the position and movement of a contact lens.

11 Retro-illumination from the iris is created by making a moderately thin slit beam and directing the beam to the iris, crystalline lens or retina at a 45 degree angle and keeping the plane of focus on the cornea. The soft reflected beam from the iris will enhance transparent corneal irregularities that are too subtle to be observed with other lighting situations. Details of corneal changes are best observed in the line between light and dark coming from the unfocused iris surface.

Uses for retro-illumination are:

•Observing deposits on Descemet’s membrane •Observing vascularization •Observing opacities on the crystalline lens •Observing epithelial edema •Observing delicate scars

12 Fluorescein application is necessary when observing the fitting of a rigid gas permeable contact lens. The slit lamp is used to view the fitting using cobalt blue filter and the method of illumination desired. Diffuse or direct focal illumination parallelpiped beam width.

13 The tip of the solution that is used to wet the strip must not touch and contaminate the strip.

14 Fluorescein can be applied by gently touching the upper conjunctiva as the patient looks down. It can also be applied when the patient looks up inside the lower lid.

15 Fluorescein has two functions, one to show the tear underneath a rigid gas permeable fitting. The tear is invisible but with the application of fluorescein and cobalt blue filter the Optician can view the pattern to determine whether or not it is a good fitting.

The other purpose is to stain where there is a loss of epithelial cells created by trauma , allergies , or disruptions in the natural metabolic state of the cornea.

16 Equipment Contact Lenses: Slit Lamp Illumination

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