Panretinal Photocoagulation: Still the Standard Against Which New Treatments Are Judged

Panretinal photocoagulation trades peripheral retina for central vision – deliberately, and with over fifty years of evidence behind the trade.

The Diabetic Retinopathy Study proved in the 1970s that scattering thousands of laser burns across the retinal periphery could cut severe vision loss from proliferative diabetic retinopathy by more than half.

Panretinal photocoagulation (PRP) remains, decades later, one of the most effective preventive treatments in all of ophthalmology.

Anti-VEGF therapy has now given clinicians a genuine alternative for some patients.

Knowing which patients still need the laser, and which can be managed with injections instead, is now a real clinical decision rather than a foregone conclusion.

What Is Panretinal Photocoagulation?

Panretinal photocoagulation is the application of thousands of laser burns across the peripheral retina, sparing the macula, to treat proliferative diabetic retinopathy and other ischaemic retinal diseases.

It is used across a range of conditions united by retinal ischaemia driving neovascularisation:

Proliferative diabetic retinopathy – the original and still the commonest indication
Ischaemic central and branch retinal vein occlusion with neovascularisation
Neovascular glaucoma, to regress the ischaemic drive behind angle neovascularisation
Retinopathy of prematurity, in a modified peripheral pattern in appropriate zones
Sickle cell retinopathy with proliferative disease

What unites all of these is the same underlying mechanism – the laser interrupts a shared final common pathway, not just diabetic disease specifically.

Mechanism of Action

The logic of the treatment is counter-intuitive on first encounter: destroying tissue to preserve function.

Ischaemic peripheral retina secretes VEGF and other angiogenic factors, driving abnormal new vessel growth at the disc and elsewhere
Laser burns destroy the oxygen-hungry outer retinal photoreceptors across a large peripheral area
Reduced peripheral oxygen demand allows the remaining choroidal circulation to adequately oxygenate the thinner residual retina
This reduces the ischaemic drive for VEGF production, causing regression of neovascularisation over weeks to months
The treatment does not restore any lost peripheral function – it converts ischaemic, VEGF-producing tissue into scarred, quiescent tissue

Explaining this trade-off clearly is essential, because patients understandably resist a treatment framed as “burning the retina” until they understand what it is protecting.

Indications and Evidence

The Diabetic Retinopathy Study established that PRP reduces severe visual loss in proliferative diabetic retinopathy by more than half compared with no treatment
The Early Treatment Diabetic Retinopathy Study refined timing, showing high-risk proliferative disease benefits from prompt treatment while very early proliferative disease may sometimes be observed
High-risk characteristics guiding urgent treatment include neovascularisation of the disc of a defined extent, or any neovascularisation with vitreous or preretinal haemorrhage
The DRCR Retina Network’s Protocol S demonstrated that anti-VEGF monotherapy achieves visual outcomes non-inferior to PRP in proliferative diabetic retinopathy over two years, with fewer visual field and peripheral vision side effects

Protocol S is the study that genuinely changed practice – it did not replace PRP, but it proved anti-VEGF was a legitimate primary alternative rather than just an adjunct.

Procedure

Planning

Confirmation of proliferative disease and high-risk characteristics on dilated examination and, where available, ultra-widefield imaging
Discussion of the anti-VEGF alternative where appropriate, factoring in the patient’s ability to attend frequent follow-up

Laser Application

Several thousand burns are placed across the mid and far periphery in one or more sessions, typically staged over two to four visits to reduce the risk of acute complications
The macula, papillomacular bundle and major vascular arcades are deliberately spared
Burn intensity is titrated to produce a moderate, whitish-grey retinal reaction without excessive intensity
Full treatment typically requires 1200 to 1600 or more burns in total across sessions

Follow-Up

Review at four to six weeks to assess regression of neovascularisation
Additional “fill-in” laser if regression is incomplete
Ongoing monitoring for recurrence, since regression does not guarantee the disease will not reactivate

Staging treatment across multiple sessions rather than a single mega-session is standard precisely to reduce the acute complications discussed below.

Complications

Peripheral visual field constriction – expected and dose-related, sometimes affecting driving eligibility
Reduced night vision and dark adaptation, from destruction of peripheral rod photoreceptors
Transient or, less often, sustained macular oedema following treatment, particularly with aggressive single-session laser
Choroidal effusion and transient angle-closure, more likely with heavy treatment delivered in one sitting
Pain during treatment, usually manageable with topical anaesthesia and, when needed, sub-Tenon or peribulbar block
Inadvertent foveal or vascular arcade burns from poor technique, causing permanent central field loss

Field constriction and impaired night vision are not complications in the strict sense – they are the expected cost of the treatment, and patients need to hear that distinction explicitly.

PRP Versus Anti-VEGF: Choosing Between Them

Anti-VEGF avoids the peripheral field loss and night vision impairment of PRP, an advantage for younger, working patients
PRP delivers a durable anatomical effect after a defined treatment course, without a requirement for indefinite injections
Anti-VEGF requires sustained adherence to frequent injections; disease reactivates rapidly if treatment lapses, whereas PRP’s effect persists even if follow-up is interrupted
Combination treatment – anti-VEGF to control acute disease activity with staged PRP for durability – is commonly used in practice, particularly where follow-up reliability is uncertain

The choice increasingly comes down to a single practical question: can this specific patient be relied upon to attend injections indefinitely? If not, PRP’s durability becomes the deciding factor.

Prognosis

PRP remains a highly effective treatment when applied at the right stage of disease.

Adequately treated high-risk proliferative diabetic retinopathy has a substantially reduced risk of severe vision loss compared with untreated disease
A minority of eyes fail to regress fully and require additional laser or adjunctive anti-VEGF therapy
Visual field and night vision effects are permanent, and patients should be counselled about this before treatment, not after
Long-term outcomes are best when PRP is combined with tight glycaemic and blood pressure control, since these remain the dominant drivers of overall diabetic eye disease progression

Fifty years on, PRP is still the treatment that reliably prevents blindness at scale – anti-VEGF has added options, not replaced the need to understand when the laser remains the right choice.

References

Diabetic Retinopathy Study Research Group. Photocoagulation treatment of proliferative diabetic retinopathy. Ophthalmology. 1981.
Writing Committee for the DRCR Retina Network. Panretinal photocoagulation vs intravitreal ranibizumab for proliferative diabetic retinopathy (Protocol S). JAMA. 2015.
Early Treatment Diabetic Retinopathy Study Research Group. Treatment techniques and clinical guidelines for photocoagulation (ETDRS Report 3). Ophthalmology. 1987.
Panretinal Photocoagulation. EyeWiki, American Academy of Ophthalmology.
Diabetic Retinopathy, Proliferative. StatPearls, NCBI Bookshelf.