Indirect ophthalmoscopy

Indirect Ophthalmoscopy

sanket parajuli

Introduction

• Simplest form is the hand held condensed lens combined with direct ophthalmoscope.

• Forms real inverted(vertically) and reversed (laterally) image with greater field of view.

• Monocular or binocular• Important role in performing retinal examination• Wide field of view• Dynamic and stereoscopic view of entire fundus• Portable

Development

• Ruete – 1852• Mono-ocular• Independent light source

Giraud-Teulon :1861• Binocular

Schepens -1951• Head mounted • Binocular• Illumination and observation system• Basis of modern indirect ophthalmoscope

Optics : Based on Gullstrand’s Principle:

a. Illumination system:• Main aim to minimize bothersome

reflection and backscatter –

• Illumination system involves• three separate beams passing through the

patient’s pupil1. Illumination beam2. Two separate observation beams : one for

each of examiner’s eye

Optics cont…• Observation beam and illumination beam--separated at the corneal and lens plane • Dilated pupil required to separate both beams until they intersect at the retina• Because examiner’s eyes are farther apart and two viewing beams exits patient’s pupil• This instrument incorporates a simple system of mirror that widens the separation and

matches examiners' pupil

Optics

The illumination beam enters a small part of the pupil and does not overlap with the observation beam, and thus minimizes bothersome reflection and backscatter.

B. Observation system:1. Contrast2. Inverted image3. Field of view4. Magnification5. Stereopsis

1. Contrast

• Since Observation beam path different from illumination beam path --- glare degradation from reflection and backscatter is minimized

• Examiner must learn to tilt handheld lens strategically to avoid reflection from the surface of the lens itself.

• Antireflection coated lens minimizes reflections, from about 4% of incident light to 1%

2. Inverted image

Hand held condensing lens • Real and inverted image of fundus• Commonly used lens: 20D

Image Through Indirect Ophthalmoscope

3.Field of view• Indirect ophthalmoscope (Emmetrope) using +13D condensing lens is 25 degrees-

Emsley

• Field of view= d/F– d is the diameter– F the focal length of the handheld lens.

Field Of View In Indirect Ophthalmoscope

The tangent of angle of field of view equals lens diameter divided by focal length.

4.Magnification

• Ratio of Fundal object /aerial image = ratio of focal length of patient’s eye / focal length of condenser lens

• Or inversely proportional to power of eye (60 D) and handheld lens

• Thus, for an emmetropic eye and a 20 D lens, the magnification = 60 D/20 D = ×3;

• for a 30 D lens, the magnification = 60 D/30 D = ×2.

Magnification of various condensing lens powers

Condensing lens power (D) FOV Angular Magnification(X)+14.00 35.90 3.8 (approx.x4)+20.00 70.80 3.0 (approx.x3)+30.00 53.20 2.1 (approx.x2)

Magnification depends upon

5. Stereopsis • Stereoptic visualization - enhanced if patient’s pupil dilated

• Light beam from dilated pupils directed through handheld lens and into the two eyepieces

• Prisms then redirect two beams into examiner’s eyes

• A smaller distance between two eyepieces than IPD, reduces stereopsis by about 1/4th

Controls

• Regardless of manufacture - has same basic control units– Headband fitting– Viewing system: customizable– Illuminations system

Head band fitting

Head band:• Adjustable with two knobs• Back: avoids unwanted movements on tilting head• Top : vertical adjustment• Rests just above the ears • Headset is equipped with +2.00Ds oculars for focussing.

Viewing system

Viewing system adjustment:• To adjust height and angulation• To adjust visual pathway-aligned with pupil

Adjustment of eye piece with examinter’s inter pupillary diatance (IPD)

• Adjust one eye at a time• Use and outstretched hand and thumb as a reference point• Shut one eye• Slide eyepiece of open eyes so that tip of thumb falls within

the center of visual field• Repeat with the other eye

Adjustment of eye piece with examinter’s inter pupillary diatance (IPD)

• Adjust one eye at a time• Use and outstretched hand

and thumb as a reference point

• Shut one eye• Slide eyepiece of open eyes

so that tip of thumb falls within the center of visual field

• Repeat with the other eye

Illumination system

• Adjustment of light source• 5 features of illumination control

Illumination system cont…

1. Reostat :• Mounted on head set or set

on battery or power supplyFunction:• On/off• Continuous adjustment =

controls illumination


2. Horizontally mounted knobs on either side

• The vertical angulation of light is adjusted relative to the field of view

• Place the light beam in upper part of field of view for optimum visualization


3. Adjustment of spot size:Largest spot: – Cooperative patient– Dilated pupil

Smaller spot: – Photophobic– Undilated pupil


4. Adjustment of filteri. Red free filter: ii. Yellow filteriii. Cobalt blue filteriv. Diffused apparture

Illumination system-filter

i. Red free filter:

• Increases contrast in viewing retinal vessels

• Highlights retinal hemorrhages


ii. Yellow filter:

Reduces photophobia in light sensitive patients


iii. Cobalt blue filter:

fluorescence angiography in children under general anaesthesia


iv. Diffused aperture:– For beginners– Broader illumination : allows

easier movement of condensing lens without losing fundal view

In addition:

• Teaching prisms

• Video indirect ophthalmoscope:– Live onscreen teaching and recordings

• Spectacles mounted Indirect ophthalmoscope– Very portable

• Cordless Indirect ophthalmoscope

Clinical Examination Techniques

1. Preparation of patient2. Examination of fundus

Preparation of Patient

Consent and counsel• Bright light• Indentation can be painful• Examiner stands behind patient’s head (supine)• Patient may be in sitting or supine position.• Begin examination with lower illumination

– Reduces patients discomfort– Allows retina to adapt

• Increase illumination once patient is accustomed with light

Examination of Fundus

• Illuminate fundus without condensing lens = fundal glow

• Hold lens (20D) facing white rim toward the patient

• Placing patient’s pupil + condensing lens + illumination beam together at imaginary straight line (conjugacy of pupil)

• Slowly pull the lens until fundus is viewed– With 20 D – 2 to 4 inches (5-10cm)

Technique of holding the condensing lens

• A. elevating upper eyelid with third finger of the hand hold along the lens while retracting the lower eyelid with the thumb of free hand

• B. elevating the upper eyelid with the thumb of free hand while retracting the lower eyelid with the finger of the had holding the lens

• Image is horizontally and laterally inverted

• Examiner stands at head end• Inferior retina is viewed first• Work all way round at 180 degrees• Optic disc and macula• Mapping maybe done by inverting the paper to locate the exact area.

Scleral Indentation• Thimble scleral depressor• Pencil tip type• Mainster S or double ended flat• Q tips, coins,paper clips

Scleral Indentation

• Enhances visualization of the extreme periphery of the retina.• Enhances kinetic evaluation of the retina• A small hole or tear near the ora serrata or near the vitreous base may be overlooked

without scleral indentation.• It may be hazardous in eyes recently operated on for cataract.

• Principle:– Appropriate position of indenter– Indentation on correct direction

Procedure-Indentation

Ask patient to gaze in direction opposite to where we want to indent

Place indenter in skin crease

Push indenter back up to the globe

Ask patient to switch the gaze to the site of indenter

Apply very gentle pressure

Helps view up to the ora serrata

Scleral indentation cont…• Sequence of circumferential scleral indentation A. examination of superior periphery – indentor tip placed• Superonasally(1)• Superiorly (2)• Superotemporally(3)

B. examination of inferior periphery-• indentor tip placed:• Inferotemporally (4)• inferiorly (5)• Inferonasally (6)

C. examination of periphery in horizontal meridians by placing the indentor tip nasally(7) then temporally(8)

Drawing The Indirect Ophthalmoscopic Fundus

• Invert the retinal chart on the patient’s chest • View, then draw, an initial landmark: supero-nasal blood vessel of the posterior

pole• Follow the vessels anteriorly and continue to draw their bifurcation and branches

in one quadrant• Repeat for the remaining quadrants• Using scleral depression, locate the blood vessels already drawn in each meridia

and sketch their terminal branches• Draw the ora serrata• Reexamine any lesions and sketch its border and details in relation to the blood

vessels and other landmarks already drawn

• Vitroretinal drawing chart is placed on the chest of patient (supine)so that examiner can draw the image that is seen through the condensing lens.

Methods for recording observations

Color codes for fundus drawingRed : • retinal arterioles• Attached retina• Retinal hemorrhage• Microaneurysm• Retinal break/hole

Blue:• Retinal venules• Detached retina • Outline of retinal break/hole

Orange : Elevated neovascularization

Purple: flat neovascularizationYellow: exudates/edemaGreen : Vitreous opacities (hge)

Brown: pigmentation, detached choroid

Black:• Ora serrrata• Drusens• hyperpigmentation

Limitations

• Needs pupil dilation hence inappropriate for patient with shallow AC.

• Needs a lot of experience to master.• Limited magnification.

Optical and observation characteristics of ophthalmoscopes

Instrument Image Stereopsis FOV MagnificationMDO Upright No 50 15XMIO Upright No 120 5XBIO Yes 300 2.5X

and invertedReversed

DO IO

Magnification X 15 X 2-5

Depth of focus Small large

Image Erect virtual Real inverted

Lens Not used Used

Field of view Small large

Illumination weak Strong

DO IO

Working distance Close to patient 30-40cm

Stereopsis absent Present

Resolution low High

Media opacities Image obstructed more Less image obstruction

Myopia Less field of view Not affected

Hyperopia More field of view Not affected

Area of field of focus Only 2 disc diopter About 8 disc diopter

References 1. Ophthalmology – Yanoff and Duker 3rd edition2. American Academy of Ophthalmology, practical ophthalmology 3. Ophthalmology Investigation and Examination Techniques-Bruce James, Larry

Benjamin4. Parsons’ Diseases of the Eye, 22nd Ed5. Internet sources

Thank you

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Indirect ophthalmoscopy