- Laser types.....Pascal, subthreshold
- Laser ..inadequate diabetic control
- Ideas that may help to improve control
- Planning laser..diabetic control
- Planning PRP laser
- certain clinical situations
- Laser PRP..how much, some ideas
- laser settings for proliferative retinopathy
- PRP laser..preventing macular oedema
- Laser PRP and visual field loss
- Lasering through a cataract or vitreous haemorrhage
Laser Treatment for diabetic retinopathy for professionals
These are giving better results than laser for both diabetic maculopathy and proliferative retinopathy!
The commonest laser is Argon Green, wavelength 530nm, but other wavelengths can be used. Other types of light were used before laser was introduced. There are two new types of laser that seem very helpful.
First, the PASCAL
laser, which can apply several hundred burns quickly, and seems ideal BJO
2010. It is also much less painful BJO
2010. Pascal macular
grids. Pascal, fewer sessions for PRP BJO 2011 Nerve fibre Retina 3011.
Secondly, a subthreshold diode laser with a longer wavelength may be best for both macular and PRP laser. There are an increasing number of reports that subthreshold laser is safer for macular oedema.
The benefit is from the lower power used, not the different wavelength difference. Burns of shorter duration certainly produce less retinal damage are are probably more effective (2010), but need more burns.
Less damage subthreshold Retina 2012. Subthreshold laser, even PRP, is recommended for milder retinopathy, but if the retinopathy is severe heavier laser burns will be needed.
Subthreshold is safe Retina14 Eye15 Eye10. Subthreshold PRP laser is unlikely to cause macular oedema or severe epiretinal membrane formation. Heavier burns (greyish white), which are needed for more aggressive proliferation, cause macular oedema in 20% of eyes.
It is absolutely vital that diabetic control is addressed. If a patient is under the care of an very experienced diabetes specialist nurse/doctor, there may be no improvements that can be made. But almost by definition, patients must have had control that is less than perfect, as it is rare with good control to develop retinopathy.
These are the standard targets (HbA1c, blood pressure (BP), exercise, healthy diet, exercise, good mental health etc).
Why is HbA1c/BP control poor? Certain clinical situations are common.
For good results, as far as possible these issues have to be addressed.
- Most patients presenting in 2020 with proliferative retinopathy have psychological problems, such as depression, anxiety, or schizophrenia or none-acceptance of their diabetes. (Mentally well patients have controlled their diabetes better to prevent such a problem.)
- Patients have too much else going on their lives, who are struggling with day to day problems, so they have not bothered with diabetic control (this may be very busy at work, someone else ill at home, etc) .
- Patients with inadequate diabetes care support from professionals.
- Patients whose professionals are ill themselves, with leukemias filling in.
- Type 2 diabetes diagnosed late..complications are present at time of diagnosis.
- Patients moving from one practice to another (who are not really bothered).
- Disorganised diabetes care.
- Patients who have not accepted their diabetes, and do not test glucose levels and adjust insulin .
- eating disorders/omitting insulin to lose weight
- patients with very poor education
- ASAP liaison with the diabetic team..whoever is providing the care
- For all patients using multiple insulin injections and who test their glucose regularly, the new glucose sensor is highly recommended here.
- if HbA1c is high, a gradual drop may be best (current advice, limited evidence, this may change). However, it is more practical just to lower it the easiest possible way, accepting it may drop quicker than ideal for the eyes.
- 3-12 months, diabetes education courses
- 3-6 months after starting laser, a modern insulin regime, perhap sa pump with a sensor (but dont get the sugar too low until the retinopathy controlled: new-onset tight control with exacerbate the retinopathy).
- if the BP is higher than target, increase medication every 2-4 weeks until controlled
- psychologist/psychiatrist if problems severe
- obesity...expert help best; low self-esteem plays a significant role
- show patients their retinal photos (or another very similar)
- whilst people may not be receptive certain times, at other times, perhaps a year or two later, they may be
- address smoking
- nine steps for success
- patients need baby steps: perhaps 1-2 weekly visit to their diabetes doctor/nurse, making small changes each visit. This may need to be carried out over 6-12 months.
- Use stories to illustrate ways forward
- when a problem is found (e.g. poor control, smoking) compliance is likely to be ~3 x higher if an appointment is made there and then, and give the appointment to the patient. Often this is not possible, but merely mentioning the problem is much less effective. Thus we should be making appointments with the diabetes specialist nurse or the Stop Smoking clinic during our retinopathy consultation, is we want good compliance.
We need to consider the rate of progression of retinopathy. With perfect control, there should be no/very little retinopathy progression. We can use UKPDS and DCCT data (and other papers) to calculate progression rate as opposite. But progression rate may change:
- if the HbA1c drops 3%, the retinopathy will progress much more quickly. This applies to the 3-4 years after starting good diabetic control, but after this time progression rate will reduce considerably.
- Pregnancy tends to lead to more rapid progression.
- sudden increases in blood pressure (usually due to decreased renal function), may also lead to more rapid progression.
- on the other hand, a type 1 patient diabetic for 40 years with reasonable control, should have more slowly progressive retinopathy
- anyone with good BP/HbA1c for 3-4 years: progression should be very slow and most patients with 4y of good glucose control, low BP, and not smoking will not have active retinopathy. It takes 3-4 years of such good control to stabilise the condition...such patients can be discharged from the laser clinic and just monitored by screening programs
- a certain degree of retinopathy may have developed in a patient
- a long duration of diabetes (e.g. 40y) (will progress slowly)
- with newly diagnosed diabetes (and recently high HbA1c) (will progress rapidly as HbA1c drops)
- poor control for a few years
- poor control for years, even is this was may years ago: 'legacy' effect
- good control...but was poor in the last 3 years
- For the same degree of retinopathy, progression rates may be very different, and laser should be increased in eyes expected to deteriorate rapidly, as in the table below.
- Shorter pulses produce less retinal damage, Muqit 2010.
Progression rates of microvascular disease
Eyes, kidneys, neuropathy etc
- 1% HbA1c rise= ~37%
- 1mm blood pressure >115mmHg systolic =1.1% increase
- Smoking...each cigarette = ~20% increase
- sleep apnoea plays a significant role
Progression rate varies despite patients having similar retinopathy appearance at any one time
|duration of diabetes||progression rate|
|40y reasonable control||slow|
|newly diagnosed diabetes now well controlled HbA1c was 10, now 7||rapid|
|poor control for a few years (HbA1c 9%)||intermediate|
|good control...but was poor in the last 3 years||rapid|
|good control...but was poor in the last 3 years..started insulin recently||rapid|
|blood pressure rise recently||rapid|
|Good control in last 3-4 years HbA1c 7%, BP 130/75, non-smoker||normally no progression whatsoever|
|pregnant (good control before conception)||may be rapid|
|pregnant: poor control before conception and control better now||extremely rapid|
Enlarge Calculating the amount of laser: increase if the retinopathy is progressing rapidly (Good HbA1c control is essential in the long term, but may increase the progression rate for 1-3 years. Retinopathy will generally stop progressing completely in non-smokers after 3-4 years of good control.)
PRP laser treatment was the main treatment for proliferative retinopathy (new vessels) or moderately severe pre-proliferative retinopathy, although increasingly anti-VEGF injections are taking over.
It helps to think ahead....how much treatment is needed in the short (and long) term. Rather than carry out 1200 burns or anti-VEGF and see the result, best results are likely if the treatment is carried out early. Some patients need a lot of laser or anti-VEGF, some a little. This summarised in this paper, Eye 2011
"Following top-up PRP treatment, regression rates varied according to severity: 75% for mild PDR (n=6), 67% for moderate PDR (n=14), and 43% in severe PDR (n=3).
What is maximum laser?
In descriptions on this page, 5000 large or 18000 smaller lighter burns are given as the estimate for treatment of most of the peripheral retina (with laser carried out in multiple sessions as on this page). But this is a very approximate figure..some patients may have 5000 burns and a lot of space is left (and they may need more laser), some may have no space after fewer. Please take this into account when interpreting the examples below.
These figures are for the trans equator lens, the easiest to use for PRP laser. Each lens has different magnification (Scanlon, p121). The Mainster 165 is reported to be the ideal lens now.
To achieve complete disease regression, mild PDR required a mean of 2187 PRP burns and 264 mm ablation area, moderate PDR required 3998 PRP burns and area 456 mm), and severe PDR needed 6924 PRP laser burns (836 mm;). Conclusions Multiple 20-ms PRP treatments applied over time does not adversely affect visual outcomes, with favourable PDR regression rates and minimal laser burn expansion over 18 months. The average laser dosimetry and retinal ablation areas to achieve complete regression increased significantly with worsening PDR." (DK now uses a lot more much smaller lighter burns. )
In an excellent review, essential reading for professionals, Eye 2011, the amount of laser can be calculated. The study was based on patients with an HbA1c current and recent <10%. Higher HbA1c patients may be expected to need a lot more laser. The paper describes laser in terms of retinal area that needs treatment, but this difficult to judge clinically. However, for significant nvd/e, most of the peripheral retina needs laser.
For the <10% HbA1c patients, in the Manchester study,
- early mild proliferation...2000 pascal burns 1-2 session, subthreshold
- moderate nv...4000 burns in 4 sessions, subthreshold
- more aggressive nv...6000 burns in ~6 sessions, moderate burns but heavier than subthreshold, mild grey-white. Theses heavier burns (greyish white) cause macular oedema in 20% of eyes.
But remember, patients in higher risk groups e.g. recent HbA1c> 10, smokers will need relatively more. patients with very good control as discussed below need less.
Once there are retinal complications, such as haemorrhage and traction , vitrectomy is more likely to be needed Retina14.
A patient with very active new vessels...generally needs ~15000 smaller lighter burns/eye, soon…1st 3 sessions in 1st week. Laser is needed quickly as it is very likely there will be a vitreous haemorrhage soon. (3000/eye/session, both eyes same session). Probably needs 18000 burns/eye (much of peripheral retinal lasered) over the next 2-4 weeks.
Examine monthly after this. Even this may not be enough and new vessels may continue to grow. If so, we believe anti-VEGF may be ideal for such patients. At present we laser 3-5 sessions and examine the result, but it is probably best to try and calculate how much is needed at the onset, and carry this out.
Vitreous haemorrhage with new vessels..similar treatment to patient 1. Vitrectomy if you cannot laser through the haemorrhage (vitrectomy with endo laser).
Disc new vessels, poor control. Retinopathy will progress reasonably quickly, laser needed over ~4weeks..similar treatment to patient 1.
Disc new vessels, poor control. But will start to improve diabetic control. Retinopathy will progress even quicker with the improving control, laser needed over ~4weeks, similar treatment to patient 1. Good control helps in the long term, sometimes not in the short term.
Disc new vessels, good control for the last 4 years. Retinopathy will progress slower, may manage with 10000 burns/eye, over ~8weeks. Examine in 2-4 months to see benefit, may need more laser over next 2 years.
Severe pre-proliferative, poor control. But will start to improve diabetic control. Retinopathy will progress quickly, may manage with 12000 burns/eye, over ~8weeks. Examine in 2-4 months to see benefit, may need more laser over next 2 years. Difficult to predict outcome. Many type 2 patients starting insulin are in this position. Best to laser early in my opinion.
Severe pre-proliferative, poor control. Won't improve HbA1c, blood pressure 130 systolic. Difficult to predict, controversial. I prefer laser: 9000 burns/eye, over ~8weeks. Examine in 2-4 months to see benefit, may need more laser over next 2 years. If no laser, examine every 3-4 months.
Reasonable control, already had new vessels treated with 12000 burns, but new vessels remain. Need ~6000 more.
Reasonable control, already had 12000 burns, not much room for more laser, but new vessels persist...? Avastin. Check the peripheral retina carefully...certainly more laser if there is lots of space.
Poor control (or control poor in the last 1-3 years), active new vessels, vitreous haemorrhage, only had 9000 burns. Needs more laser. ?Avastin then laser. ?Vitrectomy ?Avastin then vitrectomy the next week. Laser other eye.
New vessels 2002, laser PRP, 3000 larger burns both eyes (equivalent to 12000 smaller lighter burns), vessels regressed. Mediocre control at this time. 2008 presents with vitreous haemorrhage. Hard to see new vessels, but there are a number of blot haemorrhages. Also, lots of unlasered peripheral retina.
Blot haemorrhages suggest continuing ischaemia and probable new vessels..therefore laser remaining peripheral retinal until most lasered.
Alternatively..same patient as patient 11 but no blot/retinal haemorrhages...could be a simple PVD pulling some 'older' new vessels...this is more likely if there are no retinal haemorrhages at all. Probably safe to watch in this case.
Age 80y, had macula laser 2 years ago. Poor control, very overweight. New vessels now....continue with peripheral laser..until most periphery lasered.
New vessels elsewhere just in one area of retina, not many haemorrhages. May manage with laser to the appropriate sector e.g. superior temporal quadrant. But all sectors with ischaemic blot haemorrhages should be lasered.
Same patient as patient 14 with good control/non-smoker for the last 20 years..generally not much laser needed.
A patient with type 2 diabetes using insulin HbA1c 9% / 75 mmols/mol with sugar levels about 9 at work. Very severe pre-proliferative retinopathy requiring laser, about to develop macular oedema.
He lifts heavy fridges and does not want to get a hypo and drop the fridge. A colleague got a severe injury in such a situation. A diabetic consultant recommended a sensor that would alarm if the glucose dropped.
Using this he could aim for sugars of 6-7 at work, achieving much better control. But patients with type 2 diabetes have to pay for thier own sensors in the UK.
Age 28, type 1 diabetes, years of mediocre control, presented with proifertive retinopathy, lots of laser. Stable. 6 months later started a closed loop insulin pupmp sensor system targeting a HbA1c of 6.7 mmol/mol.
Then developed severe macular ischaemia in one eye, so the diabetic team were asked to aim for a higher sugar for 6 months, and anti-VEGF commenced then drop gradually to 6.7. Outome awaited (April 2020).
- Increasingly anti-VEGF injections are taking over as the main treatment in many countries.
- In all the examples above, normally.....each eye each session: 2-3000 burns/eye...normally both eyes lasered same session: these are light small subthreshold burns, my current policy... 0.01 second, 2-300µ, fast repeat, Pascal ideal
- very active new vessels...~5 sessions, much of the peripheral retina needs laser, urgent (more for lighter smaller burns) with heavier laser.
- a few new vessels, reasonable & stable control (HbA1c & BP), no previous laser, 3 sessions, subthreshold.
- a few new vessels, lots of previous laser, 1-2 sessions
- severe pre-proliferative, very good control (and good for previous 3-4 years), difficult decision, 3 sessions smaller lighter burns (but generally new vessels will develop and a lot more laser will be needed perhaps 1-2years). Anti-VEGF injections are needed if available.
- severe pre-proliferative, good control, smokes 20/day, ~5 sessions
- severe pre-proliferative, poor control, ~5 sessions; Anti-VEGF injections
- pre-proliferative, other eye proliferative, ~3 sessions
- severe pre-proliferative: most people in Europe now treat with Anti-VEGF injections, or laser if they are not available.
- if the new vessels are very active most peripheral retina needs to be lasered in the next few weeks, (Anti-VEGF injections instead or in addition)
- the same settings are used for PRP laser of pre-proliferative retinopathy...see planning laser above.
- The Mainster 165 is an excellent lens for peripheral laser; the transequator is easier to use but not as good for the peripheral retina
- 0.01seconds (quite a short duration): these short burns are less painful but if ~300µ more burns will be needed than longer or bigger burns. Essentially this is copying the Pascal laser technique.
- 300mw ~300µ for PRP, short light just visible burns (or just invisible...that is visible and turn the power down a little). More of these light burns will be required than the previous policy of heavier burns.
- consider using 300mw and adjust spot size according to the burn intensity...use the size that gives the correct intensity. Aim for slight blanching, then turn power a little lower so burns are hardly visible. Very important paper, calculate the number of burns: Retina 2011 'To maintain the same total area as in 1,000 standard burns (100 ms, moderate) with a 400μm beam, a larger number of 20-ms lesions are required: 1,464, 1,979, and 3,520 for moderate, light, and barely visible grades, respectively. Because of stronger relative effect of heat diffusion with a smaller beam, with 200μm this ratio increases: 1,932, 2,783, and 5,017 lesions of 20ms with moderate, light, and barely visible grades correspond to the area of 1,000 standard burns.'
- if power is kept unchanged: smaller burns if there is a cataract (these will be more intense), larger if the retina is pigmented or the patient pseudophakic (these will be less intense).
- Larger burns can be used, with even higher power, but they should still be light burns as below.
- 3000 burns/session/eye (lighter 3-500µ burns) both eyes each session can save time
- Pascal laser seems to give a better results, with fewer sessions needed, Retina 2011. Is this because laser burns are shorter pulses or lighter? ..I think this is likely, which is why shorter lighter burns are suggested here.
- Light burns (just lighter than blanching): for these rapid 0.01 second burns, 'light' burns are best, hardly visible when first burnt but may be just visible minutes later ...see here for Bandello's paper; a few more burns may be required, but complications are significantly less.
- remember if you use a longer duration of burn, use a lower power
- If you suspect macular oedema is present, even if mild, carry out a light macular grid first and wait 2 weeks unless treatment is urgent.
- In all except young type 1 patients with healthy maculae many ophthalmologists prefer to carry out a light grid macular laser before the PRP, to prevent macular oedema. If starting laser early, this may not be necessary.
- Heavy burns produce more epiretinal membrane, and there is no benefit. Laser too light has too little an effect.
- But in severe cases, I tend to carry out 4 sessions treating both eyes each session in the first week (still 3000 burns/eye/session, very light invisible/just visible burns, with more the next week. Delaying laser makes vitreous haemorrhage likely. Lasering quickly, that is ~6 sessions over 1-2 weeks, lighter 300µ burns, means that most of the retina will have had a lot of laser before the view is obscured by the haemorrhage.
- Most routine cases without severe retinal ischaemia can have the laser applied over 5 weeks.
- Transequator for the first 2 sessions, after that use the Mainster 165 or other wide angle lens for a couple of sessions...this will reach more peripheral laser than can be reached with the transequator lens.
- After 5-6 sessions/eye with a transequator lens (or even before) the laser may become very painful...try smaller burns, with less power, still using 0.02 seconds.
- Auditing recent work two patients developed vitreous haemorrhages. In retrospect it was clear the patients did not have as much as laser as they needed, or as much in Shimura's protocol as above. In one this was prevented by cataracts....earlier indirect laser or cataract surgery and immediate laser probably should have been carried out. In the other, there was too long a gap between treatments...the patient insisted on going on a long holiday. A 6 week gap instead of a 2 week gap lead to a serious vitreous haemorrhage. Other patients have even more aggressive disease...some need daily laser, 3000 burns/session, very light 300µ burns, even in hospital if they are at risk of 'absconding', but with better screening we get very few such patients.
- Another observation...some patients are seen for follow up and everything is reported 'OK'. They then 'bleed' few weeks later. Generally these patients will have had new vessels...so if this is happening in your department, start looking for new vessels more carefully. I find a very bright Welch Allyn ophthalmoscope with a green filter picks up more new vessels than a 60d lens on a slit lamp.
- subthreshold laser: use high powers in a very brief pulse...people are trying to copy this with their argon laser...high power, short times, light burns, hence the 0.01 second pulse
- More laser is needed until the new vessels regress (DRS 89).
- Start lasering the inferior retina more heavily that the superior retina, as this will be obstructed if a vitreous haemorrhage and the superior retina is more important in preventing falls. In severe cases the superior retina will still need heavy laser.
- Except in the mildest cases do not delay by waiting weeks for a fluorescein angiogram.
- PRP laser...keep outside the macular arcade, at least 2 disc diameters from the disc. Laser within this area..see macular grid...should be with much smaller burns.
- See pregnancy
- Use Avastin in severe cases.
- this is usually unavoidable in severe cases...aggressive new vessels need lots of PRP laser quickly.
- subthreshold burns..lighter burns (more light burns versus fewer heavier) are unlikely to produce macular oedema or epiretinal membranes, and are ideal in the none-severe cases.
- start with grid macular laser unless young type 1 with healthy macula (if Anti-VEGF injections are not available)
- A number of patients seem to develop macular oedema even with lightish burns, but fewer than with heavier laser, ....no hard evidence. OCT examination shows that unfortunately most patients seem to develop increase retinal thickness after PRP laser, and some loss of vision.
- Anti-VEGF is taking over as the main treatment, with half the amount of macular oedema and neovascularisation
- The Restore study indicated anti-VEGF injections (Avastin/Lucentis etc) will help reduce macular oedema more than laser (laser probably helps in the long term).
- Anti-VEGF injections will help in most cases of active proliferation.
If there is macular oedema before starting laser, this is likely to increase with PRP laser, which is one of the main reason anti-VEGF injections are taking over as the main treatment. This paper is important, indicating that oedema of para-foveal areas makes post-PRP laser loss of vision much more likely, and sometimes this is permanent. This may mean we should carry out a macular grid first, and wait for the oedema to reduce...but very often there is no time to do this (active proliferation requires laser soon). This paper, to my mind, implies that it is important to grid laser anyone with para-foveal macular oedema, in the pre-proliferative stage, so that the macular oedema has time to settle by the time full PRP laser is essential.
Macular oedema is very common after PRP, even after macular grid laser. Sometimes this is because the PRP was too heavy, as Bandello above. (Low blood pressure will help a little...even <130mmHg systolic. Lighter burns as above have further reduced this problem substantially clinically (no hard evidence for this..and as above OCT does demonstrate oedema/increased retinal thickness in many patients).
As above, in all except young type 1 patients with healthy maculae many ophthalmologists prefer to carry out a light grid laser before the PRP, to prevent macular oedema. Carry out the grid and PRP laser at the same session in very severe cases or if you think the patient is not likely to come back again.
Eyes with considerable ischaemia are far more prone to macular oedema. If macular oedema is present anti-VEGF injections are really essential.
Laser burns enlarge. If there is active proliferation, there is absolutely no choice but to laser. But once much of the retina is lasered, the patient will have lost a fair amount of visual field.
At this stage, further laser will cause much more significant field loss: if 60% of the retina is lasered, lasering 10% of the the remaining unlasered retina will cause 25% more field loss.
For this reason, a number of our patients have had to stop driving, and have great difficulty with their side vision. To prevent this, we are starting to use Avastin. We hope 3 injections (after much of the retina has been lasered) will stop proliferation indefinitely. We are waiting to confirm this! All our Avastin patients get new vessel regression for a while, but unless they are well lasered the proliferation occurs later...the Avastin only delays progression.
Everyone is hoping subthreshold laser PRP will enable lighter burns and hence maintain a better visual field. The PASCAL laser produces quicker burns...may be this will be helpful. PASCAL laser seems to be a big step forward, but the laser costs 3 times as much as a regular laser, and inadvertent macular laser is a possibility with the current model.
When lasering through a vitreous haemorrhage or cataract
- make the spot size smaller
- if this does not work, increase the duration of the burn, to 0.05 seconds
- Using the very short pulses of 0.01 seconds may produce very intense burns...one moment you are lasering through blood using the correct power, but the next moment when there is less blood the burn becomes too intense. so care is needed.
- See "One or 2 intravitreal injections of 1.25 mg Bevacizumab with PRP are associated with rapid regression of VH and may reduce the need for vitrectomy."
- For some reason laser at a slit lamp may not be possible
- after a lot of PRP laser the retina becomes very sensitive and further laser becomes extremely painful
- Also for some patients, proliferation may be remain very active despite lots of laser...consider indirect laser with an anaesthetic. However, as above, we would like to use Avastin rather than extremely heavy laser.
- If laser extremely painful, indirect laser, may be 2/3 occasions/eye will be much less painful.
- general anaesthetic for bilateral indirect laser, peribulbar for unilateral.
- routine more
When carrying out PRP laser it is very important to treat the fellow eye, this important paper suggests. Unless the retinopathy is highly asymmetrical, which is most unusual, laser is important. Furthermore, the same paper suggests that 4-6000 3-500μ burns are needed to prevent retinopathy developing to maintain vision in the long term. This is because the worst visual results were in the second eye to be treated.
If the retinopathy is very asymmetric suspect carotid artery stenosis.
Remember to address diabetic control. Anti-VEGF injections are the main treatment, but if not available laser as here (as previously regularly used):
- If there is diffuse macular oedema, or extensive oedema, grid laser is best
- Follow up for the average case 2 months.
- At 2 months, if there is a poor laser response as seen clinically, and the macula oedema has not reduced, repeat the grid laser. Do not repeat if plenty of burns visible.
- At 2 months, if the macular oedema has not responded at all AND there is a good laser response with are enough burns, consider an FFA to identify if more laser is needed (or intravitreal steroid etc). If the laser is going to work, the oedema should be reducing at 3 months.
- Exudates take much longer to go (statins/fibrates are important), but start to reduce if treatment adequate.
- Macula oedema is best measured by OCT. Clinical judgment is helpful; FFA can help.
- If the leakage just affects a small part of the macula, as in circinate retinopathy, 'focal' laser is applied. The same settings (as below) are used, but the laser confined to the circinate/affected area.....for focal laser...similar settings, fewer burns. Focal laser is used, for example, on an area of circinate retinopathy: this is essentially the same as a grid but only a sector of macular laser is carried out, but again no laser within one disc diameter of the fovea.
- 2-3 sessions may be needed over a year; after 3 sessions little further macular grid laser is needed in the years to come, whether or not there is oedema. FFA is carried out if there is a poor response to laser after 2 grid laser treatments.
- As with any retinopathy, control of the diabetes (sugar, HbA1c, blood pressure, cholesterol) is essential for success of this treatment.
- Pan-retinal photocoagulation (PRP) may be needed as as part of the treatment for severe or diffuse macular oedema. If there are no ischaemic haemorrhages, and the maculopathy is the only retinopathy present, it is not likely to help. Eyes with a lot of ischaemic blot haemorrhages have very ischaemic central retinae, and often have new vessels that are not obvious clinically, or often develop them over the next two years, and PRP laser helps to prevent this. At present I would recommend the PRP is carried out 2-4 weeks after grid laser, whether of the heavier, as sometimes pan-retinal laser can increase oedema. In theory, if carried out in this manner, oedema should not increase, with provisos such as (poor control).
- No laser is needed within 1 disc diameter of the fovea , except for lasering the occasional microaneurysm >500 µ from fovea.
- Very severe macular oedema...grid laser does not help. IVT had not proved helpful overall. Avastin for persistent macular oedema; resistant cases intravitreal steroid (?implants).
- After laser, burn size enlarges. This is called burn creep. Over the years, the creep can spread in towards the fovea. For patients years ago this did not matter as they were very ill, but patients who improve their diabetic control have a longer life expectancy, and this 'enlargement of burns' or burn creep may threaten their sight many years after laser.
- Many doctors laser outside the macular area if there is considerable ischaemia (shown by blot haemorrhages). In a way this distinction is academic: any eye with a lot of retinal ischaemia will develop proliferative changes in 3-18 months, and this will need laser. Many ophthalmologists carry out PRP laser if there is substantial peripheral ischaemia (my preferred policy).
- OCT is very useful. Previously we waited for obvious maculopathy as seen on a slit lamp before recommending laser. But we know laser seldom improves sight. So logically we should laser earlier, as soon as there in ANY (except the mildest) thickening as seen with OCT. With very slight OCT thickening (macular oedema), show the patient the scan. Offer laser; encourage the best glucose and blood pressure control (& no smoking, weight loss, physical exercise). Laser if the patients wants. Then 4 months later review ...if the retina is thicker, and no laser was carried out, then obviously laser is now needed. Outcomes in macular oedema are best with anti-VEGF treatment
- See results of laser Eye 2011
Remember to address diabetic control. Anti-VEGF injections are the main treatment, but if not available laser as here (as previously regularly used):
- Subthreshold diode laser, with nearly confluent very light burns, probably produces the best results. This is seldom available in the UK.
- Area-centralis lens is an excellent lens for diabetic maculopathy
- 200-300 x 50µ burns for a maculopathy grid, less for focal
- 0.01 seconds
- see techniques
- light burns, subthreshold. Laser first to see a visible impact, then turn the power lower so the burns are invisible. The subthreshold diode laser uses infrared laser with very short burns....it is not clear clear whether it is the wavelength that helps, or using a shorter pulse time, or using lighter burns. Most lasers can be adjusted to provide a very short pulse eg 0.01 seconds (my current time) and a low power (subthreshold): few departments have access to a diode laser.
- This study suggests that it is important to laser/laser around microaneurysms
- No laser within 1 disc diameter from the fovea.
- this study suggests that lasering microaneurysms a little closer than this (but still greater than ~500µ from the fovea) may be helpful.
- Autofluorescence is seldom available but may help ?identify the FAZ (foveal avascular zone)
- Include laser to adjacent non-perfused areas (outside the grid laser area, that is above, below, and temporal).
- Light invisible subthreshold burns.... one of the reasons for using lighter burns is that they cause less atrophy in the much longer term. It is difficult to know how heavy to make the laser...but burns that do not show on a fluorescein angiogram later were probably too light, so you can tell retrospectively. Burns that were too heavy cause significant atrophy. Even 'perfect' burns may produce very slight pigmentation, but significant pigmentation indicates excessive power. Burs at the most intense should be only just visible, they may still need to be a little lighter (invisible). Planning laser is more important...the same area should not be treated twice. Some experts recommend subthreshold diode laser burns that are nearly confluent (but at present I still leave one burn space gap between such invisible burns).
- Low power for pigmented retina (often 50mw), especially if pseudophakic and media is clear; higher power if there is a cataract or macular oedema (usually <180mw). Average power 60mw. More power needed according to the amount of oedema present. Thus the power (milliwatts): an Afro-Caribbeans retina in a pseudophakic eye with mild oedema needs a low power; a Caucasian retina with a cataract and considerable oedema needs a much higher power.
- The laser power used now is lighter than originally described in the ETDRS p92.
- Combine laser with Avastin
A treatment plan for diabetic maculopathy modified after Simon Harding, 2007 and Olk, (Now replaced with anti-VEGF injections):
give information sheet and record this in notes
or diffuse maculopathy?
circinate, small area of oedema
Anti-VEGF main treatment, laser may be needed additionally: grid laser
generally include laser shots to microaneurysms if >1 disc diameter from fovea & scatter laser to non-foveal areas of non-perfusion/IRMAs (usually temporal retina)
reassess ~6 months
Reassess 2 months. If poor laser response as seen clinically, repeat (i.e. if laser burns not visible and maculopathy no better;) do not repeat if plenty of burns visible. Anti-VEGF main treatment always needed at this stage.
Reassess 4 months later, consider repeating laser if oedema/thickening remains or not reduced with OCT, otherwise FFA.
oedema persists, FFA
treat leaky areas as identified with FFA; consider anti-VEGF drugs; very ischaemic macula with very large avascular foveal zone...very difficult to achieve improvement..consider PRP
Monitor all patients for deterioration/proliferation.
Create boundaries for the laser....must keep away from the fovea.
Some exceptions..may need a little laser to microaneurysms slightly within this are..but only a few shots of laser , and not near the fovea.
Extend the boundary a little horizontally
Laser always moving from the fovea (again, this is to prevent foveal laser). Subthreshold laser is invisible so you need to remember which area has been treated.
Standard grid laser, with extra shots further out, more laser in ischaemic area ... areas of microaneurysms and haemorrhages
Having laser is a very traumatic experience, especially PRP laser. Trento and others investigated this (EASDec 2003) and found
- it is not so much as that the laser is distressing, but knowing that the eyes are seriously affected by diabetes. A good explanation and counselling may help, but this is often a very serious development for individual patients.
- the laser itself is not that painful for the first few sessions (I would add that lower powers are used now, as above).
- short burns are less painful ....0.02 seconds for PRP as above. The Pascal laser is much less painful BJO 2010.
- Paracetamol does not help.
- laser can become very painful after the first 5 sessions. In my experience no pain relief helps, but small burns and a lower power help.
- Indirect laser is very helpful when the laser has become very painful, perhaps after 6 sessions. Should we use subtenons: Richardson 09
- Smaller lighter burns can be used instead of indirect laser...though obviously a lot of the retinal periphery must be lasered as above.
- PRP laser thins the retina Retina 2013
- visual field loss as above
- inadvertent foveal laser
- macular oedema as above
- laser too heavy...this can be avoided....choroidal detachment (and this may lead to complications such as angle closure glaucoma).
- Macular laser can lead to CNV, but this is unlikely with the lower power settings used now.
Read this book
Can be very helpful