OP1201 – Basic Clinical Techniques

Posterior eyeDr Kirsten Hamilton-Maxwell

Today’s goalsBy the end of today’s lecture, you should be able to

explainWhy examining the posterior eye is importantBasic construction and optical principles of the direct

ophthalmoscopeHow to use it to examine the posterior eye and how to record

resultsHave some awareness of normal and abnormal posterior eye

conditionsLimitations of direct ophthalmoscopy

By the end of the related practical, you should be able toAssess and record the health of the posterior eye using direct

ophthalmoscopy efficiently and accurately

OphthalmoscopyWe have used the direct ophthalmoscope to

examine the anterior eyeToday we will look at the primary function of this

device – examination of the posterior eyeFirst, we need to know how it works

How ophthalmoscopy works (the optics)Ophthalmoscope construction – lens rack, aperture stops and

filtersBasic anatomy of the posterior eye

Optics of the eye

Light from infinity enters the eye through the pupil and is focussed on the retina (in an eye with emmetropia only)

Optics of the eye

If a light source could be placed on the retina, it would exit the eye along the same path

Light reflected from the retina behaves in the same way

Optics of the eye

The light reflected from the retina would be seen by an observer located along the same axis

However, the observer would block the light source (why the pupil is black)

Optics of ophthalmoscopy

Concave mirrorwith central hole(or semi-silvered mirror)

Light source at 90deg

Alternatively a prism

Optics of ophthalmoscopy

Divergentlight, if subjecthypermetropic

Reflectedlight

source

Convergentlight, if subject

myopic

Divergentlight

Convergentlight

Parallellight

Focussedon retina

Corrective lens is placed along pathway

If clinician and patient are both emmetropic then:

Lens rack powerIn order for reflected light exiting the patient’s

eye to be parallel, the patient’s ametropia (refractive error) must be corrected

In order for the parallel light entering the clinician’s eye to be focussed correctly, the clinician’s ametropia must be corrected

Need a corrective lens equal to sum of clinician’s and patient’s refractive errors

As individual subjects and observers have a range of refractive errors, need a range of lens powers (i.e. a lens rack)

Ophthalmoscope headClinician Patient

Lens rack(~-20D to +20D)

Mirror (or May prism)

Variable brightnesslight source

Filters, aperture stops, miscellaneous

Aperture stopsControl the size of the beamLarge, medium or small

Use largest for external and internal examination If pupils small, reduce aperture size

Use large or medium for internal examination

Use smallest for foveal examination

In general, use the largest beam possible for the best view

FiltersRed-free filter

Blocks structures below Retinal Pigment Epithelium (RPE) and enhances contrast of retinal blood vessels and haemorrhages

Helps in cup to disc (C/D) ratio assessmentHelps identify nerve fibre layer (NFL) dropout – a

sign of glaucoma

Blue filterCan enhance reflectivity of optic disc drusenFor use with fluorescein/fluorescein angiography

Yellow filterReduces UV exposure

MiscellaneousGraticule

Used in assessment of eccentric fixation

Determine relative size and distance of fundus structures

Slit beamHelps in assessment of 3-D

structures e.g. optic cup

Basic ocular anatomyAnterior eyePosterior eye

Posterior eye anatomy

Optic discMacula – no blood vessels, darker pigment than surrounding area

Blood vesselsVeins are darker than arteries, usually larger

Vessel crossing

Temporal Nasal

Retinal nerve fibre radiations

Examining the posterior eye

Examples

Recording results

How to do ophthalmoscopyAssume that the anterior eye examination has

just been completedThe lens power is +10DYou are 10cm away from the eyeThe patient is looking 15deg up and to their temporal

sideMedium to large aperture stop

First step is to locate the red reflex from the fundusWe are aiming to bring this into focus = retinal

structures visible

What you seeDirect ophthalmoscopy gives an erect, real,

magnified image15x magnification with a 5deg field of view

through one eyeDepends on Rx

Higher magnification but smaller field of view for myopes Lower magnification but larger field of view for hypermetropes

Pupil size Better field of view with larger pupils BUT field of view is always small

No stereopsis

What am I looking for?LensVitreousOptic disc

SizeC/D ratioMarginsColour

Blood vesselsA/V ratioCrossingsCalibre/tortuosityReflectivityLeakage

MaculaWhole areaFovea and foveal reflex

PeripheryRetinaChoroid

How to view the lens

Retro-illumination

VitreousGet as close to your patient’s eye as you canWith the red reflex visible, reduce lens rack

power by 1D steps (towards zero, or plano)As you do this, you will focus at different depths

within the vitreous until finally the fundus comes into focus

If you and your patient are both emmetropic and not accommodating (almost impossible when you are learning), the lens power should be zero when you are in focus

Vitreous floaters

Will look like a dark shadow among the red/orange reflexWill move when the patient moves their eyes

Scan the fundusBe systematicUse the disc as an orientation pointIf the patient is looking 15deg to the temporal

side and you move in along the horizontal visual axis, you should find it straight away

All of the blood vessels originate in the disc, so follow them from here. If you get lost, return to the disc and start again

Ask the patient to look in the 9 cardinal directions to assess the periphery

Make sure no gaps in fundus coverage: when following vessels, scan perpendicularly.Scan from arcades towards fovea.

Blood vesselsLook for

Calibre – vessel width and regularityTortuosity – “wriggliness” of vesselsArtery/Vein (A/V) ratio

Compare width of artery (red) to vein (darker red) Should be about 2/3

Crossings Does the vein change shape when crossed by an artery?

Can be compressed leading to nipping

Reflectivity – is the vessel sheath clear or opaque?Leaking – haemorrhages, exudates

Normal vessels

More normal vessels

Abnormal blood vessels

More abnormal blood vessels

RetinaSometimes the word “retina” is used to mean the

same thing as “fundus”Anatomically, the retina is a transparent layer

containing photoreceptors and connecting cellsThe retinal interface with the vitreous may reflect

light like a wet surface, but you will not usually see the retina itself unless there is a problem

Retina

Myelinated nerve fibres

Retina

Retinal detachment

MaculaCones onlyFovea in the centreMore pigmented than surrounding retinaNo blood vessels

Supplied by the underlying choroid and choriocapillaris

Ask the patient to look directly into the light In young healthy eyes, you will see a yellow

reflection = foveal reflex Note its presence and whether it is bright,

moderate or dim Use graticule to assess centrality of the

fovea

Normal macula

Darker at macula

Note: This is also a tigroid fundus… choroidal blood vessels are visible (view usually blocked by the RPE)

Macula disease

ARMD - drusen

Recording ophthalmoscopySize and distance is

recorded in terms of disc diameters

Direction is recorded according to a clockface in hoursDo not flip for RE and

LE

Locating a lesion - example

This lesion is1DD wide,

0.5DD high1DD above the

foveaOR 3DD from

the disc at 10 o’clock

Recording your findings

The area you can see with the direct

ophthalmoscope

Disc

MaculaClock directions

Disc – for next week

39 39

Use descriptive termsWrite something for

everything!

Dropout in glaucoma,myelination at disc margin.

Crossings: nipping insystemic hypertension

Cupping and notchingin glaucoma

Swelling and blurredmargins in papilloedemaand optic neuritis

Vessel walls: sheathing in systemic hypertension, leakage and neovascularisation in diabetes.

Bifurcations: embolisms,branch occlusions

Pigmentation changesin retinitis pigmentosa

Haemorrhagesin diabetes, vessel occlusion,hypertension

Myopic crescentin myopia

ARMD, drusen,macular holes

Retinal tears,detachments

Anterior ischaemic opticneuropathy in diabetes

Vessels

Optic disc

Fovea

Background/periphery

Retinal nerve fibre layerTumours

Vitreous

Asteroid hyalosis, floaters,haemorrhages

LimitationsNo stereopsisSmall field of view

Not all of the fundus covered, even by a thorough systematic technique

Large lesions can be missed entirely, especially if the colour change is gradual

Cannot see very far into the peripheryIndirect ophthalmoscopy is preferred for fundus

examination

Elliott, Sections 6.4 to 6.5, 6.20Become familiar with the procedural steps

Memorise anatomical structures