Specular Reflection (from Endothelium and Ant. Lens) Retro Illumination (From Fundus and Iris)

Specular Reflection (Endoth)

Specular Reflection from the Corneal Endothelium. Reflections from Cornea, Lens, Tear prism, From iris and Sometimes from lashes can look like scratches on the cornea. In order to get the best view of the corneal endothelium we deliberately find the 1^st and 2^nd purkinje image (PI) (from the epithelium and endothelium of the cornea).

How to get specular reflection (Endoth)

At the centre of the cornea we need to position the microscope off axis. So we usually perform temporally- moving both illumination system and observation system  towards the bright reflex. Head for the bright reflex. Try to ignore the bright epithelial reflection and concentrate on the endothelium. Bring the slit to the PI- easiest if bring from centre of cornea outwards. Like PP want to widen till epithelium and endothelium just meet. This maximises the amount of endothelium seen

Why is specular reflection a monocular technique?

I = R for only one eyepiece

Guttata

cells dropped out, not in shape. Endothelial cells don’t regrow. Endothelial guttata associated to fuchs endothelial dystrophy..

Polymorhpism and Polymegathism

Polymorphism- Changes in shape. Polymegathism- Changes in size.

Advantages and disadvantages of Specular Reflection (endoth)

Advantages

›Useful for checking for changes in endothelial cell especially in CL aftercares (polymorphism/ polymegathism)

›Endothelial cells are not replaced- vital to keep an eye on them

›Cheaper than a confocal microscope (specular microscopy)

Disadvantages

›Only checks a very small portion of the endothelium (can only set up at the PI)

›Need good SL and skilled operator to get a good image

Specular Reflection (endoth) Tips

Widen beam. want the beam to be at the PI or just nasal (if the illumination system is temporal). maintain focus.

Specular Reflection (Ant. Lens)

Creates orange peel effect due to texture not colour. Scratches are lashes.

How to get specular reflection (Ant. Lens)

we view the surface we are interested in at the point where there is maximal light reflected. In the case of the Anterior Lens this is where the 3^rd Purkinje Image is formed. Again i=r so the microscope must be placed at the same angle as the illumination

Advantages and Disadvantages of specular reflection (Ant. Lens)

Advantages

›Useful for checking for deposits on the anterior lens e.g.:

›pigment deposits in suspected anterior uveitis

›pseudoexfoliation syndrome (PEX)- deposits on the anterior lens surface associated with an increased risk of glaucoma

Disadvantages

›Only looks at surface of the lens- not at cataract within it

Specular Reflection (Ant. Lens) Tips

use big movements of ill system to find point at which front surface of lens section shimmers most before widening slit

Don’t Allow Px to look towards microcope

produce in examiner’s eyepiece

reduce brightness

demonstrate a large area of orange peel

Direct Illumination

Pointing the light directly at the thing we want to observe. Used in most techniques (incl. all those up to now). Good for high contrast features. Not great for fainter targets which might be lost in the glare/scatter

Indirect Illumination

Used to view low contrast features. 3 types of indirect illumination:

Proximal Illumination- caused by scatter from the direct beam

Retro Illumination- light reflected back from ocular structures which act like a diffuse reflector

Proximal Illumination- from scatter of the light from retro illumination (light that is bouncing back from ocular structures)

Retro Illumination (Iris) Steps

A.Direct illumination

B.Scatter from the direct beam illuminates features around the beam causing “proximal illumination”

C.Diffuse reflections from anatomical structures (in this case the iris) illuminate corneal features from behind

D.This reflected beam also scatters causing more proximal illumination

Retro Illumination Iris

Retro illumination from the iris uses the iris as the ‘diffuse reflector’ and allows us to illuminate the cornea from behind. It allows us to look in detail at low contrast features which may be lost in the glare of direct. It also silhouettes features against a bright background.

How to do Retro illumination (iris)

V shape is formed. White/blue side of the V is the direct beam through the cornea. Duller orange side is the retro illumination. Cross illuminated to maximise separation between limbs of the V. Medium to low contrast features lost in the glare. Seen best in retro illumination. Silhouettes the keratic precipitates (KPs)- also useful for other low contrast targets like pigment

Retro Illumination (Iris) Filters

Red free (green) filters on the illumination system can improve the contrast of blood vessels. Red features appear blacker. Especially useful if the patient has dark irides.

Advantages and Disadvantages of Retro Illumination (Iris)

Advantages

›Allows low contrast features like keratic precipitates to be examined

›Allows limbal blood vessels to be checked for neovascularisation – particularly in CL aftercares

Disadvantages

›Works less well with dark irides where less light is reflected

›Generally only performed at 4 and 8 o’clock positions, checking the entire limbus is hard and time consuming

Retro Illumination (Iris) Tips

cross illuminate

Beam bright and wide

maintain focus at high mag

Retro Illumination (Fundus)

use the reflected glow from the fundus to retro illuminate the lens.

How to do retro illumination (fundus)

Set up a short, fat slit in focus at 10-11 or 1-2 o’clock on the pupil/iris border

The LOCS III Grading System for Cataract

Used to grade cortical and PSCO/ PCO cataract (BUT not NS).

Advantages and Disadvantages of Retro Illumination (Fundus)

Advantages

›With a good glow from the fundus, opacities are easily detected

›Good way of checking for Pigment Dispersion Syndrome and other iris disorders/trauma

›Easy to perform on dilated patients

Disadvantages

›Very difficult to perform if patient has small pupils and/or a dark fundus (best on a dilated patient)

›Gives no information on the depth of opacities

Retro Illumination (Fundus) Tips

Don’t Panic if no red glow- don’t worry- NOT REQ’d FOR EXAM- you might not on subjects with darker irises. In this case you just need to set it up correctly

little separation between obs. and ill. systems

take account of the change in pupil size as the light is increased