Diabetic retinopathy screening NSF-based training

Anatomy and physiology

Tunde Peto

Head of Reading Centre

Anatomy and physiology of the

normal human eyeKey issues for discussion

• Review the gross anatomical structures within and related to the eyeball and discuss their basic function

• Review the basic physiology of refraction and vision

Learning outcome

• Identify the different structures of the eye and discuss their basic function

• Identify different anatomical structures on teaching slides

Basic Science in relation to eye disease: the normal retina and

visionKey issues for discussion

• The normal anatomy of the retina• Photoreceptors and their biochemistry• Physiology of vision including colour

visionLearning outcome

• Identify normal retinal structure on teaching slides

• Reflected light translated into mental image• Pupil limits light, lens focuses light• Retinal rods and cones are photoreceptors

Vision

Figure 10-36: Photoreceptors in the fovea

• Rods – monochromatic, provide night vision: most numerous in periphery, sees all shades of grey and white; see in dark and around us

• Peripheral changes might not affect the vision at all

• Laser treatment and retinal detachment might result in visual field loss

• Cones – red, green, & blue; color & details, most numerous in macula; you need very few for good vision!

Photoreceptors

Photoreception and Local Integration

Figure 10-35: ANATOMY SUMMARY: The Retina

Retina: More Detail

Figure 10-38: Photoreceptors: rods and cones

• Bipolar• Ganglion

– Movement– Color

• Optic nerve• Optic chiasm• Optic tract• Thalamus• Visual cortex

Vision: Integration of Signals to Perception

Figure 10-29b, c: Neural pathways for vision and the papillary reflex

The aging retina: Age Related Maculopathy (ARM) and Macula Degeneration (AMD)

Key issues for discussion• Normal changes in the aging retina• Abnormal changes in the aging retina• The constituents of drusen • Geographic atrophy • Neovascular AMD Learning outcome• Identify age related changes in the retina• Identify and discuss different types of drusen • Identify geographic atrophy• Identify and discuss the main features of neovascular AMD

Hard drusen (<63 mikron)

Normal SLO image

Hard and intermediate soft drusen (63-125 mikron)

Large soft Drusen on the posterior pole

Watch it developing over the years

2 years later

5 years later

7 years later

10 years later: some areas atrophied

Geographic Atrophy

Neovascular membrane at the fovea

Neovascular membrane at the fovea

FFA of the neovascular membranes: R eye: occult, L eye classic membrane

Right eye: occult membrane

Left eye: classic membrane

Fibrovascular scar and secondary atrophy

Neovascular membrane on SLO imaging

Pigment epithelial detachment: colour image

Pigment epithelial detachment on FFA

Pigment epithelial detachment: SLO image

Vascular occlusion

Key issues for discussion• Learn normal vasculature of the eye• Discuss most common systemic causes of vascular problems in

the eye• Discuss vein occlusion• Discuss arterial occlusion• Discuss clinical implications of these diseases Learning outcome• Identify normal and abnormal vascular structures in the eye on

teaching slides• Identify strategies to deal with these diseases

Central retinal vein occlusion:

Introduction

• dilated, tortuous veins & haems in all 4 quadrants• ischaemic (iCRVO) vs. non ischaemic (niCRVO)• ischaemic = non perfused, haemorrhagic• non-ischaemic = perfused, venous stasis retinopathy

Epidemiology (EDCCS)

• 2 per 1000 > 40 years, 5.5 per 1000 > 64 years

• 33% ischaemic, 67% non ischaemic

• 13% < 45 years, 11% 45-54 years, 76% > 55 years

Clinical features• reduced visual acuity• RAPD• retinal predictors of ischaemia

– degree of intraretinal haemorrhage– venous dilatation– venous tortuosity

• as chronicity develops – IRMA, microaneurysms, collateral vessels

Complications

• macular oedema, ischaemia

• NVE / NVD (6-7%)

• iris neovascularisation (NVI), neovascular glaucoma (NVG) (21%)

• cilioretinal artery occlusion

• combined with CRAO

Large areas of ischaemia on FFA

Iris neovascularisation

Comined with CRAO: cherry red spot with white macula

Classification• ischaemic vs non-ischaemic

– two ends of a spectrum

– elderly: if severe, retinal capillaries decompensate, iCRVO

– young: if mild or moderate, retinal capillaries withstand increased venous pressure, niCRVO

• young vs old 40 yrs, 64% final VA 6/9

– > 40 yrs, 40% iCRVO

Good perfusion on FFA

Poor peripheral perfusion on FFA

Differential diagnosis

• Anterior ischaemic optic neuropathy / optic neuritis / optic nerve invasion

• asymmetrical diabetic retinopathy• ocular ischaemic syndrome• severe anaemia, leukaemia• Waldenstroms macroglobulinaemia• carotico-cavernous fistula

Branch retinal vein occlusion

• A cause should be found for it!

• Most common caused: diabetes mellitus, hypertension and lipid abnormalities

• Investigations need to be done by the referring physician, not in screening setting, however, you need to notify the physician

• You will find asymptomatic old BRVO-s in screening setting

Embolic disease: local protocol, but requires GP notification so risk factors for stroke and sight threatening disease can be addressed

The normal optic nerve and its pathological changes

Key issues for discussion• Learn the normal anatomy of the optic nerve • Discuss the function of the optic nerve and its connection

to the brain • Discuss major illnesses affecting the optic nerve • Discuss the main features of the glaucomatous changes of

the optic nerve Learning outcome• Identify the main features of the optic nerve and discuss

the function • Identify normal optic nerve on teaching slides • Identify the main features of the diseases optic nerve

The Normal Optic Nerve Head

•  The optic nerve head can be imagined as a ‘plug-hole’ down which over 1 million nerve fibres descend through a sieve-like sheet known as the lamina cribrosa. These fibres are then bundled together behind the eye as the optic nerve which continues towards the brain.

•  The retinal nerve fibres are spread unevenly across the surface of the retina in a thin layer. As the nerve fibres converge on the edge of the disc they pour over the scleral ring and then down its inner surface. This dense packing of nerve fibres just inside the scleral ring is visualized as the neuroretinal rim.

•  The inner (with respect to the centre of the optic nerve head) edge of this neuroretinal rim marks the most central of the nerve fibres. This edge is usually sloped, yet may be range from an overhang to vertical to a gentle slope towards the centre of the disc. This inner edge marks the cup edge.

Scleral RingOuter edgeInner edge (outer edge of disc or neuroretinal rim

Cup EdgeChange in direction of blood vessel

Neuro-retinal rim

 

The Scleral Ring

• This ring is usually pale allowing it to be distinguished from the neuroretinal rim tissue which is pink. The ring may not be visible in a given disc image, or the visibility may vary in different areas of the circumference of the disc. It is often easier to see on the temporal side of the disc than on the nasal side.

Scleral ring

As vessels bridge the scleral ring, they often make a slight change in direction (black arrow) which may be a clue to its inner edge, The change in colour is also evident in this case (arrows mark inner and outer edges) Blurring of the image may occur due to media opacity or resolution of the image- this can make appreciation of the anatomy difficult.

  

Outer

Inner

The Cup edge• This is undoubtedly the most difficult contour to identify, and is subject to more variability than the

disc edge.

• The inner edge of the neuroretinal rim (=cup edge) may be sloped (especially on the temporal side of the disc) or vertical. In some cases the edge may be an overhang.

• The most effective way of drawing this ring is to identify certain points on the cup edge where you are sure of its location, and then using a dot-to-dot procedure link up these points into a ring. First look for a blood vessel, preferably a small to medium-sized one (large vessels do not hug the surface and may not be tethered to the surface and therefore are unhelpful). Trace its path across the scleral ring and then over the rim tissue- at some point it will change direction as it bends inward towards the centre of the disc. If the slope is shallow this will be a gradual change in direction, however if vertical it will be an obvious bend, and in the case of an overhang it will suddenly disappear from view. It is the point of maximum change of direction of the vessel that marks the cup edge. When viewing the disc in stereo, the edge of the cup can often be clearly seen in areas where there are no vessels as a guide.

• There can be a temptation to mark the cup edge where the colour changes from the pink of the rim to the pallor of the cup. In many situations this would be correct, yet in some situations the edge of pallor is not necessarily the edge of the cup, and hence it is better to rely on vessels and stereo cues as described above.

• The following images illustrate these points.

The cup edge

 

The Cup Edge: 3 blood vessels here show the edge of the cup:The points of maximum inflection (bend) are marked by arrows.

Cup Edge:In this very clear image, the arrows mark the cup edge. This illustrates that occasionally large vessels may obscure the edge from view, and in this case one should mark points of certainty either side of the vessel and link these up.

 

The cup edge

Optic nerve head assessment

Dr. Patricio SchlottmannResearch Fellow

Glaucoma Research Unit

Overview

• Glaucoma definition

• Anatomy

• Risk factors

• Cup/disc

Definition

• Glaucoma is a chronic, progressive optic neuropathy that manifests by a characteristic Visual Field loss and distinctive structural changes recognizable at the level of the Optic nerve head or the Retinal Nerve Fibre Layer (RNFL)

Definition

• Chronic: having a progressive course of indefinite duration

• Progressive: tending to become more severe

• Optic neuropathy: disease of the of the optic nerve

Definition

• Optic neuropathy

– The ganglion cells and their axons are the damaged structures

– Other cells within the retina are also affected

Anatomy

Anatomy

Risk Factors

• Major risk factors for developing glaucoma are:

• 1. elevated intraocular pressure

• 2. African descent

• 3. family history of glaucoma

• 4. increased age

Risk factors

• Elevated intraocular pressure

Risk factors

• African derived individuals

– Glaucoma is 4 times more prevalent– Is usually more severe – Starts at earlier age– Progresses more rapidly

Risk Factors

• Family history of glaucoma– A first degree relative affected by glaucoma

increases the risk of developing the disease in the future

– Patients should be questioned about the severity of glaucoma in the affected relative

Risk Factors

• Increased age

– Prevalence increases with age

– It is 10% of subjects over 80 years

Cup/disc

• Definition – Relationship between cup area and disc area

Disc

Cup

Cup/disc

• Examples

0.1

0.80.7

0.50.3

0.95

What to look for?

• Large cup/disc– >0.7-0.8

• Asymmetry– >0.2-0.3 between eyes

• Haemorrhages

What to look for?

• Notches– Focal loss of fibres

• Areas of thinning– Diffuse thinning of the rim

Screening for glaucoma

• Too many false positives

– 2% subjects over 40

– Advanced condition is easier to diagnose

What to do with a suspect?

• They will need referral to eye department

– Phenotyping

– Decision on treatment or observation

Phenotyping

• Complete evaluation of the patient– Medical history– Risk factors– Medications– Scans– VF– Clinical examination w/dilation

3 hours visit

Examples

Examples

Examples

Examples