Diabetic Retinopathy

Diabetes Mellitus is a common disease with serious ocular complications. It is one of the leading causes of legal blindness in the United States and much of the rest of the world.

Qn 1: Do all patients with Diabetes Mellitus develop eye complications?

Most studies found that the longer the patient had Diabetes Mellitus, the higher the chances of developing Diabetic Retinopathy. If the patients had Diabetes for 17 – 25 years, about 90% developed some degree of retinopathy. Diabetes does not just affect the retina. Diabetes Mellitus has been found to promote cataract formation, an increased incidence of open angle glaucoma etc. Unfortunately, it is mainly the effect of Diabetes on the retina that causes blindness.

Qn 2: How does Diabetic Retinopathy cause blindness?

Diabetic retinopathy causes blindness through a few mechanisms:

  1. Leakage of proteins and lipids through damaged small vessels causing macula swelling and damage (maculopathy).
  2. Bleeding into the vitreous gel, causing blockage of light transmission. Diabetes and the Retina
  3. Formation of scar tissue which may pull on the retina and cause a retinal detachment.
  4. Decrease in blood flow to the central retina (macula ischaemia).

Diabetes Mellitus affects the small vessels of the eye. By damaging the small vessels of the eye, it causes weakness of the vessel walls, with leaking of blood and blood proteins occurring. When the walls of the vessels are severely damaged, blood flow through these damaged vessels cease and the retina suffers from a lack of oxygen. The retina may respond to the lack of oxygen by producing cer tain substances which encourage the growth of new vessels. Unfor tunately, the new vessels which develop are fragile and bleed easily.

A series of pictures and simplified illustrations are shown to illustrate the various degrees of severity of Diabetic retinopathy:

Diabetic Retinopathy/Figure 1

Picture 1: Normal retina

Note the healthy looking central part of the retina (macula). The vitreous gel is clear without any opacities seen.

 



Diabetic Retinopathy/Figure 2

Picture 2: Non-Proliferative Diabetic retinopathy with severe maculopathy

Mild to moderate Non-proliferative diabetic retinopathy is not a serious stage of diabetic retinopathy. However, the patient as shown in Fig 23 cannot see well because of the leakage of proteins and lipids from the small vessels which have collected at the macula. This causes swelling at the macula and the photoreceptor cells important for vision are affected.

 



Diabetic Retinopathy/Figure 3

Picture 3: Severe non-Proliferative Diabetic retinopathy (preproliferative retinopathy)

This picture shows severe non-proliferative diabetic retinopathy.

This is the stage when the retina starts to be deprived of oxygen and the signs of this can be seen in the picture: the vessels are tortuous and beaded, there is abnormal fine vessel formation and numerous large retinal haemorrhages. The patient has to be watched carefully as progression to the next severe stage occurs in half of these patients in the next 24 months.

 



Diabetic Retinopathy/Figure 4

Picture 4: Proliferative Diabetic Retinopathy

Proliferative diabetic retinopathy is a severe stage of diabetic retinopathy. It is characterised by severe lack of oxygen of the retina and the formation of new vessels. These new vessels are very fragile and bleed easily, causing blood to collect in the vitreous gel. This will cause loss of vision until the blood is cleared by the eye or removed by surgery. Unfortunately, blood in the vitreous gel stimulates inflammation and the formation of fibrous scar tissue in the vitreous gel. This scar tissue may pull on the retina and cause a tractional retinal detachment.


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Qn 3: How does laser treatment help severe Diabetic Retinopathy?

The only proven treatment for severe Diabetic retinopathy is laser treatment.

It must be emphasised that laser treatment does not usually improve vision. The aim of laser treatment is to stabilise the diabetic retinopathy and prevent progression to more severe retinopathy with possible blinding consequences.

There are two broad types of laser treatment:

  1. Focal/grid laser. This is done to ‘seal’ small areas of leaking blood vessels and to reduce the swelling of the retina.
  2. Panretinal photocoagulation. This is more extensive laser treatment. It involves extensive laser treatment to the midperiphery and periphery of the retina. It is postulated that this treatment reduces the amount of retina that lacks oxygen, hence decreasing the stimulus for new vessel formation.

In the pictures below, they show both focal (Fig 1) and panretinal photocoagulation treatment. (Fig 2)

Diabetic Retinopathy/Figure 5
 

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Qn 4: What are the complications of laser treatment for Diabetic retinopathy?

Complications of laser for diabetic retinopathy are not common. The commonest complaint of patients during and after the laser treatment is the discomfort experienced. This is often described as a ‘sharp, pinprick’ sensation when the laser is applied. There will also be some discomfort experienced due to the bright flashing lights during the procedure..

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Qn 5: When is surgery necessary for severe Diabetic Retinopathy? What are the risks of such surgery?

Surgery is necessary for severe Diabetic Retinopathy in the following circumstances:

Diabetic Retinopathy/Figure 6
 
  1. Prolonged Bleeding in the Vitreous Gel. (Fig 28)

    Normally, most ophthalmologists will wait at least 4 – 6 weeks for the vitreous blood to spotaneously clear. The period that most ophthalmologists will wait depends on the severity of the retinopathy present and the urgency to start laser treatment. If very severe retinopathy is present, the vitreoretinal surgeon may choose to perform the vitrectomy much earlier as laser treatment can be performed during the operation. Once the blood clears, extensive laser treatment will be applied to retard the progression of the diabetic retinopathy and cause regression of the new vessels. Unfortunately, some patient’s vitreous blood does not clear up and the ophthalmologist is worried about the retinopathy progressing without any laser applied. A vitrectomy is performed and the blood is removed, with laser treatment done during the vitrectomy. The diagram (Fig 29) illustrates the procedure being performed.

 
 
Diabetic Retinopathy/Figure 7
 
  1. Retinal Detachment involving the macula.

    Retinal detachments that develop in diabetic retinopathy are usually of the tractional type, (Fig 30) in which scar tissue pulls on the retina and causes a detachment. This type of detachment is usually stable and slowly progressive. Unfor tunately, in some individuals, it may progress to involve the central part of the eye (macula) and cause a drastic drop in vision. In other individuals, the constant traction may cause a hole to form in the retina. This will cause the detachment to suddenly progress rapidly. In the above situations, the vitreoretinal surgeon will have to surgically intervene to prevent blindness. A vitrectomy will need to be done to remove scar tissue with laser treatment applied to the retina, possibly a scleral buckle done and long acting gas/silicone oil to fill the vitreous cavity and tamponade (apply pressure on) the retina. Such complex cases have a poorer prognosis and the patient should discuss this thoroughly with his vitreoretinal surgeon.

 
 
Diabetic Retinopathy/Figure 8
 
  1. Severe glaucoma developing due to severe diabetic retinopathy.

    Usually, in very severe diabetic retinopathy, due to the lack of oxygen, the iris starts to develop new vessels and this causes a very difficult and severe type of glaucoma called neovascular glaucoma (Fig 42). Without very extensive laser/cryotherapy of the retina to destroy the oxygen starved retina, such diabetic eyes will inevitably worsen and become blind. In some of these patients, it may be difficult to laser the retina due to the accompanying bleeding into the vitreous gel. It may be necessary to then perform a vitrectomy to remove the blood and perform extensive laser treatment of the retina. The prognosis for these patients is unfortunately very poor.

 
 
Diabetic Retinopathy/Figure 9
 

A new method of treatment for neovascular glaucoma due to severe diabetic eye disease involves the use of Vascular Endothelial Growth Factor (VEGF) inhibitors injected directly into the eyes of patients with neovascular glaucoma. It showed promising results with regression of the new vessels at the iris (a classic feature of neovascular glaucoma) and a reduction of the high intraocular pressures, allowing the ophthalmologists an opportunity to either perform more panretinal laser photocoagulation treatment and/or to do complex glaucoma surgery. Potential side effects of the injection include the risk of retinal tears/retinal detachment (about 1 in a 100) and the risk of severe eye infection (endophthalmitis — reported less than 1.3%). The prognosis for patients with neovascular glaucoma due to severe diabetic eye disease is still guarded (uncertain) despite the latest treatment with VEGF inhibitors.

 

The risks of such surgery are the same for any vitrectomy performed

  1. The risk of infection is about one in a thousand cases. Unfortunately, when this happens, the chances of complete blindness is very high.
  2. The risk of a retinal detachment is about 2-3%. Further surgery will be needed to repair these detachments but prognosis worsens with every additional surgery performed. There is also the risk that despite further surgery, the patient will still become completely blind.
  3. The risk of rebleeding is high in severe diabetic retinopathy. Even when the vitrectomy has successfully removed all the blood, there is a 50 % risk of a rebleed occurring immediately after the surgery. Rebleeding into a previously vitrectomised eye will often clear spontaneously over several weeks.

    It is often difficult for the vitreoretinal surgeon to predict how long the recurrent haemorrhage will take to clear as this is partly a function of the amount of blood present and the overall health of the eye. If there is evidence of a retinal detachment present, prompt surgery is required.

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