Ординатура / Офтальмология / Английские материалы / Eye Essentials Diabetes and the Eye_Steele, Steel_2008

Retinal photocoagulation for DR

●ivenous obstruction (again this should hopefully be clarified on angiography).

Complications

Para central scotomata are common after treatment close to the foveal centre. Patients should be warned that they may notice grey scotomata around their central vision for a few days to weeks after treatment.These usually however fade with time, but not always.

Transient worsening of vision can occur due to a transient increase in oedema following treatment; again this usually improves.

Choroidal neovascularization can occur and patients should be specifically warned of this complication if they have existing age-related macular degeneration (AMD). In this situation the choroidal neovascular membrane (CNVM) can actually be just part of the AMD natural history and not part of the laser treatment (Fig. 8.9). High intensity small burns should be avoided which can rupture bruchs membrane increasing the likelihood of choroidal neovascularization. Also it should be noted that CNVM can occur spontaneously in patients with severe diabetic macular oedema (DMO).

Sub retinal fibrosis can occur, but again this can occur in diffusely oedematous maculae as part of the diabetic maculopathy disease course. Similarly epiretinal membrane formation can occur (Fig. 8.10).

Fig. 8.9 Small choroidal neovascular membrane post focal laser treatment — there was later spontaneous regression of membrane and a return to

6/6 vision.

Management of diabetic retinopathy and diabetic maculopathy

116

Fig. 8.10 (a,b,c,d) Pre (upper) and post (lower) laser views of patients with PDR and severe maculopathy — note right subretinal fibrosis at site of central plaque exudate post laser.

Vas at last follow-up R 6/60, L 6/36.

Laser scar expansion can occur, especially in myopic patients as discussed above.

Exudate deposition at the foveal centre can occur in extremely oedematous retinae after treatment, and large exudates close to the fovea are also a risk factor. In patients with grossly oedematous maculae, or exudates very close to fixation, the option of fractionating the maculopathy treatment in a

couple of sessions should be considered to try and avoid the risk of sub-foveal exudate deposition.

Increased ischaemia can occur rarely after maculopathy treatment, especially in patients with mixed maculopathy.

Retinal photocoagulation for DR

If ischaemia is suspected an angiogram should be arranged so that

this complication can be discussed with the patient if they wish. 117 This is best undertaken with the patient looking at the angiogram

with the operating clinician.

Colour vision and contrast sensitivity can be reduced following laser and again should be discussed if this is relevant to the patient’s profession or hobbies in particular.

Focal laser treatment for diabetic maculopathy clearly works and the commonest cause for reduction in vision following laser treatment is actually progression in maculopathy rather than deterioration in vision secondary to laser.The incidence of iatrogenic visual acuity reduction following laser is probably

less than 1 in 300 in the author’s (D. Steel) experience.

Laser treatment of proliferative diabetic retinopathy (PDR)

Aims of treatment

The aim of PRP laser therapy in PDR is to induce involution of new vessels thereby preventing visual loss from vitreous haemorrhage and tractional retinal detachment.

Indications for PRP

PRP significantly reduces the likelihood that an eye with retinal neovascularization will experience severe visual loss.The Diabetic Retinopathy Study (DRS) Research Group, which was one of the first randomized control trials ever undertaken in ophthalmology, conclusively demonstrated the efficacy of laser PRP in PDR. After 2 years, eyes which had received 1200–1600, 500 micron PRP burns had less than half the rate of severe vision loss compared with the control eyes that had received no laser treatment (Table 8.3).The absolute risk reduction obviously depends upon the severity and natural history risk of a particular eye with retinopathy at baseline and the DRS provided useful natural history figures for this (Table 8.4).

Both the DRS and ETDRS showed that PRP should be given promptly if certain ‘high risk’ features were present and this has led to a definition of ‘high risk’ PDR (Box 8.1).

Management of diabetic retinopathy and diabetic maculopathy

Box 8.1 Definition of ‘high risk’ proliferative retinopathy

The presence of any three of the following:

●Vitreous haemorrhage.

●New vessels.

●NVD.

●NVD > 1/3 DA or NVE > 1/2 DA.

NVD are the single most important prognostic factor for the risk of severe visual loss in DR.

Retinal photocoagulation for DR

‘High risk’ PDR

1.vitreous haemorrhage;

2.any new vessels;

3.new vessels at the optic disc;

4.new vessels at the optic disc greater than one-third of a disc area in size, or new vessels elsewhere greater than half a disc area in size.

The following clinical scenarios are defined as ‘high risk’ PDR:

1.Mild disc new vessels (NVD) less than one-third of the disc area with haemorrhage.This carries a 26% risk of severe visual loss over 2 years.This can be reduced to 4% with PRP laser treatment.

2.Severe NVD greater than half the disc area without haemorrhage.This carries a 26% risk of visual loss which is reduced to 9% with treatment.

3.Severe NVD with haemorrhage carries a 37% risk of visual loss, which reduces to 20% with treatment.

4.Severe new vessels elsewhere (NVE) greater than half a disc area with vitreous or pre-retinal haemorrhage.This carries a 30% risk of visual loss, which is reduced to 7% with treatment.

New vessels on the optic disc are thus the single most important prognostic factor for the visual prognosis in PDR.

For lesser degrees of PDR the beneficial effect of the PRP is less obvious. However, these types of retinopathy can still progress. In patients with small new vessels at the optic disc without a vitreous haemorrhage, and therefore without ‘high risk’ retinopathy, the risk of progression to ‘high risk’ retinopathy, without treatment, is 59% within 2 years versus 22% with PRP treatment.

Unless ‘high risk’ characteristics are present PRP may be withheld and the patient closely monitored at 3-monthly intervals. However in the UK many ophthalmologists often perform PRP treatment at the first sign of neovascularization especially if the following features are present.

Management of diabetic retinopathy and diabetic maculopathy

1. patients are poor clinic attendees;

1202. if the other eye has severe retinopathy;

3.if cataract surgery is planned;

4.if there are a number of other indicators in the retina suggestive that a large degree of ischaemia is present and that the retinopathy is highly likely to progress i.e. severe to very severe NPDR, e.g. widespread IRMA (Figs. 8.11 and 8.12);

5.retinopathy is deteriorating and metabolic control is poor.

The 1-year risk of severe NPDR progressing to high risk PDR is 15% without treatment and about 8% with PRP (Table 8.5).The beneficial effect of PRP in patients with severe NPDR is thus less

Fig. 8.11 Multiple IRMA.

Fig. 8.12 IRMA nasally.

Retinal photocoagulation for DR

Table 8.5 Risk of progression to high-risk characteristics in

clear and usually PRP laser treatment is not given.There are however exceptions to the rule and PRP laser treatment may be considered, as with low risk PDR, if the above features are present.

Treatment technique for PRP

A standard initial PRP is approximately 1200–1600 burns of 500 microns size (Fig. 8.13).The author (D. Steel) routinely uses a quadraspheric lens which magnifies the spot by about 2x (Table 8.6).Therefore to get a 500-micron retinal burn a 250micron spot size needs to be selected on the laser console. Longer duration burns result in larger burns but with no more pain during treatment, and so PRP is often delivered with either a 0.03 or 0.08s duration as a compromise. A white grey burn

is aimed for: more intense than focal (Fig. 8.14).

The amount of PRP in any one session is dictated by a number of factors including the patient’s tolerance. In general, more initial PRP is attempted in higher risk situations, such as in patients with very high risk PDR or in patients who have a poor repeat attendance record. Less PRP is administered in one session if treatment fractionation is planned, for example if there are concerns regarding maculopathy exacerbation. In a patient with NVE only and some maculopathy it may actually be best to treat the macula first without any PRP or possibly just sector PRP around the NVE and then arrange two further PRP sessions

of 700 burns each 3–4 weeks later, or possibly even when the

Management of diabetic retinopathy and diabetic maculopathy

Laser burns in pan-retinal

122distribution: arcades to as far peripheral as possible–arcades to

equatorial retina often area of maximum ischaemia

Untreated macula area

Fig. 8.13 Diagrammatic representation of pan-retinal photocoagulation (PRP).

macular is dry, if the macula is particularly oedematous. Triamcinolone given via a posterior sub-Tenon’s injection before PRP can also reduce the risk of maculopathy exacerbation

in this situation.

Conversely, if a patient has large new vessels at the disc with a light vitreous haemorrhage, it may be appropriate to deliver 2000 burns in one session before further haemorrhage occurs. Another strategy in this situation especially if the macula is suspect would be to give 1000 burns inferiorly and then arrange for a superior

PRP 1–2 weeks later.

Similarly if a patient has iris and irido-corneal angle rubeosis, laser needs to be applied rapidly before the angle is permanently closed. Paradoxically intraocular pressure (IOP) can be raised with an open angle in an eye with angle rubeosis.These eyes often still respond well to PRP with regression of rubeotic vessels and reduced IOP. For patients with rubeosis and a hazy cornea secondary to raised IOP a useful technique is to use glycerol as

Retinal photocoagulation for DR

Table 8.6 Summary of lenses and treatment parameters

the contact lens contact solution to keep the cornea dehydrated and clearer during treatment.The aim is to get PRP on swiftly and efficiently with a local anaesthetic block if necessary (see below). Some patients prefer to have 500–600 burns in three to four sessions even if this means they are coming back each week for 4 weeks. Other patients may prefer to get the treatment completed

in one session because of problems with transport etc.

Fig. 8.14 PDR — immediately post laser.

Management of diabetic retinopathy and diabetic maculopathy

However, if there is any degree of treatable maculopathy

124present it should be ensured that macular treatment is undertaken either before the PRP is started, or at the same time as the PRP. PRP can produce dramatic RPE pigmentation and hypertrophy with a ‘surface of a moon’ type appearance (Fig. 8.15).

Pain during PRP laser treatment

All patients get some degree of pain during a PRP, which is the main difference patients notice between focal and PRP laser! The degree of pain however is surprisingly variable between patients ranging from very mild to completely intolerable. Pain is usually greater on re-treatments, whilst treating the anterior retina, in eyes with light RPE and whilst treating the horizontal midlines where the long ciliary nerves are located.

There are a number of strategies that can be tried if pain is significant:

1.If the PRP does not need to be done quickly, fractionate the treatment in a number of divided sessions.

2.When administering the PRP it is best to leave the horizontal and peripheral retinal areas until the end.

3.Reducing the duration of the burns reduces the pain, so if a patient is experiencing pain with a 0.08-second exposure then reducing the burn duration to 0.05 seconds or even 0.03 seconds can often improve things.

Fig. 8.15 Old PRP burns.