Diabetic Eye Disease

Background

• Chronic, potentially blinding retinopathy associated with prolonged hyperglycaemia and other conditions linked to the diabetes/
• Most common cause of blindness in the UK (~12-15%)
• NB Diabetics are also at higher risk of cataracts
• Patients with diabetes are now routinely screened annually for eye disease

Aetiology/Risk Factors

• Diabetes (!)
  • NB Many people who have diabetes will not have had a diagnosis- this may be an incidental finding.  If suspect, testing for diabetes should be offered.
  • The duration of diabetes is significant
    • 6% at 4 years; 73% at 14 years
  • Poor glycaemic control (persistently higher HbA1c recordings) increases the likelihood of eye disease
    • NB Don’t rely on a single HbA1c measurement to assess past glycaemic control
• Diabetic/CVS complications
  • Hypertension
  • Proteinuria (Nephropathy)
• Pregnancy

Pathophysiology

Features of Diabetic Eye Disease

• Microaneurysms
  • small dots in the superficial retinal layers
• Dot and blot haemorrhages
  • If the above microaneurysms burst into the deeper layers of the retina, small dots of haemorrhages may be seen (may appear similar to microaneurysm but flourescein angiography may be able to differentiate between the two- aneurysm will be confined, whereas haemorrhage won’t)
• Flame haemorrhages
  • Occur when microaneurysms burst in the superficial layer
• Hard exudates
  • Precipitates of proteins/lipoproteins leaking from surrounding blood vessels.
  • This usually occurs in a ‘ring’ around the macula i.e. within the arcades (maculopathy) but can occur elsewhere in the retina (classified more as retinopathy)
• Cotton wool spots
  • Nerve fibre layer infarctions (caused by hypoxia) result in a build up of axonal debris (cotton wool spots)
• Venous loop/beading
  • Occurs adjacent to areas with above abnormalities and is a predictor of neovascularisation
• Neovascularisation
  • Intra-retinal microvascular abnormalities (IRMA- not-technically classed as proliferative)
    • spidery, abnormal vessels in the retina; typically contorted with sharp corners, often crossing themselves (but not over other big vessels)
  • New vessels appearing commonly on the optic disc (NVD) or elsewhere (NVE). These can be differentiated from IRMA (Proliferative disease).
  • As far as I can tell, the main difference between IRMA and NV is that IRMA vessels are more ‘normal’ in that they don’t leak (on fluorescein angio)- they may, in fact, just be dilated capillaries.  NV are abnormal vessels.

Presentation

• Usually as loss of vision/blurry central vision
  • Painless
• Floaters may present if patient has vitreous haemorrhage/retinal detachment

NB Examine all of these patients with a slit lamp- as this can identify macular oedema (not possible with ophthalmoscope alone).  Also examine visual acuity.

Classification of Diabetic Eye Disease

• Retinopathy
  • Non-proliferative retinopathy
    • Mild (R1)
      • Microaneurysms and/or very small dot/blot haemorrhages only
        • 1+ microaneurysms
        • Few peripheral hard exudates
        • Few small dot/blot haemorrhages
    • Moderate (R2)
      • Microaneurysms
      • Dot/blot haemorrhages in 1-3 quadrants
      • Retinal (flame) haemorrhages in 1-3 quadrants
      • Venous calibre changes in 1 quadrant
    • Severe (R2)
      • Microaneurysms +
        • >4 per quadrant of dot/blot haemorrhages
        • >2 quadrants with venous calibre changes
        • Any IRMA
  • Proliferative Retinopathy (R3)
    • Neovascularisation
• Maculopathy
  • NB The features of maculopathy on examination with an ophthalmoscope are similar to retinopathy.  IT IS THE LOCATION of these abnormalities which is of importance.
    • Optical coherence tomography (OCT) scanning can better evaluate macular oedema
  • Can be classified as
    • No maculopathy (M0)
    • Observable maculopathy
      • Microaneurysms, hard exudates and small haemorrhages WITHIN ARCADES
      • (M0 includes disease known not to be caused by diabetic macular oedema- which may also present with micro-aneurysms/haemorrhages.  However, these features will usually classify as M1 disease)
    • Referable maculopathy (M1)
      • Same but WITHIN 1 DISC DIAMETER OF FIXATION (FOVEA)
      • Hard exudates are particularly concerning

Management

• GLYCAEMIC CONTROL!!
  • Try and keep HbA1c <7.5% when possible
• Laser surgery
  • Can be used for proliferative disease
  • Can still cause peripheral field constriction (and loss of driver’s license)
  • Can also cause night blindness
  • May worsen macular oedema
  • May fail
• Anti-VEGF may be useful for proliferative disease too
• Vitrectomy may be required if a large amount of haemorrhage has occurred or if there is a lot of scar tissue, causing retinal detachment

Prognosis

• Background retinopathy will usually progress to moderate/severe forms
• 50% of those with proliferative retinopathy will lose their sight within 2 years (90% within 10)
• Treatment (laser surgery) will reduce risk of visual loss from 30% to 15%.