Retina Companion Note
Macular Laser Photocoagulation in Diabetic Macular Oedema
Conventional techniques, current indications and advanced laser-delivery systems
A concept-first guide to focal and grid photocoagulation, modified ETDRS treatment, subthreshold micropulse laser, pattern scanning and navigated retinal laser.
Watch the Two-Part Lecture
Begin with conventional focal and grid photocoagulation, then continue to current indications and newer laser-delivery systems.
Conventional Focal and Grid Photocoagulation
ETDRS principles, focal treatment, grid laser and modified macular photocoagulation.
Watch on YouTube →
Current Indications and Advanced Laser Systems
Micropulse treatment, PASCAL pattern scanning and NAVILAS navigated laser.
Watch on YouTube →The Current Role of Macular Laser
Modern treatment selection begins by asking whether the oedema is centre-involving or non-centre-involving, and whether visual acuity has been affected.
Vision-impairing centre-involving DME
Intravitreal anti-VEGF therapy is generally the initial treatment because it produces better visual outcomes than prompt conventional macular laser alone. Laser may later be used selectively for persistent, safely treatable focal leakage, but it is no longer the routine first treatment. [6] [8]
Centre-involving DME with good vision
DRCR Retina Network Protocol V studied eyes with centre-involving DME and visual acuity of 20/25 or better. At two years, there was no significant difference in vision loss between initial aflibercept, focal/grid laser or observation, provided aflibercept was started if visual acuity worsened. Reliable observation is therefore reasonable in an appropriately monitored patient. [7]
The ETDRS Foundation
The Early Treatment Diabetic Retinopathy Study established focal/grid argon laser photocoagulation as the standard treatment for clinically significant macular oedema, or CSME. [1] [2] [3]
How was CSME defined?
Retinal thickening at or within 500 µm of the centre of the macula.
Hard exudates at or within 500 µm of the macular centre, when associated with adjacent retinal thickening.
When was CSME used as a treatment threshold?
In the ETDRS era, CSME identified eyes in which focal/grid photocoagulation should be considered, particularly when the centre of the macula was involved or imminently threatened.
Laser reduced the three-year risk of moderate visual loss—approximately 15 ETDRS letters or a doubling of the visual angle—from about 24% to 12%. Its principal benefit was therefore prevention of further visual loss rather than rapid restoration of normal vision. [1] [3]
From Focal and Grid to Modified ETDRS
The terminology is easiest to understand in sequence. First decide whether the abnormality requires direct focal treatment, treatment of a wider retinal area, or both. Only then consider the treatment protocol and the geometric distribution of the grid.
Treat the discrete leaking lesion
A relevant leaking microaneurysm or other focal vascular lesion is identified and treated directly.
Treat the wider abnormal retinal area
Multiple separated burns are placed over selected areas of diffuse retinal thickening, leakage or capillary non-perfusion.
Many eyes contain both patterns. Therefore, both the original ETDRS and the modified ETDRS techniques may include a focal component and a grid component.
What changed from original ETDRS to modified ETDRS?
What about mild macular grid?
Mild macular grid was a separate DRCR Retina Network treatment strategy. It tested whether a broad field of very light burns could improve oedema without directly treating individual microaneurysms.
Relevant leaking microaneurysms are treated directly, while light grid burns are confined to selected abnormal retina.
Approximately 200–300 very light burns are distributed more broadly over thickened and unthickened macular retina. Microaneurysms are not treated directly.
Clinical conclusion: modified ETDRS treatment produced a greater reduction in retinal thickening at 12 months. Mild macular grid did not replace the more selective direct/grid approach. [4]
Where do C-grid and modified C-grid fit?
These terms describe the geometric distribution of the grid component. They do not replace the distinction between focal and grid treatment.
C-grid or horseshoe grid
Grid burns are distributed superiorly, temporally and inferiorly around the fovea, while the nasal papillomacular region is spared.
Ring grid
A more complete annular grid may include involved nasal macular retina while still preserving the central foveal zone. [20]
Modified C-grid
An older and inconsistently defined term, usually referring to a lighter or more selective C-shaped grid with papillomacular-bundle sparing. It is not a formal ETDRS or DRCR protocol.
How Macular Laser Works
Conventional laser light is absorbed by retinal and choroidal chromophores and converted into heat. This produces a controlled thermal effect, principally involving the retinal pigment epithelium and adjacent outer retina.
Two complementary treatment effects
Closure of the leaking microaneurysm
Direct treatment may cause vascular-wall contraction, coagulation and thrombosis, followed by eventual closure of the selected leaking microaneurysm.
Modification of dysfunctional retina
Grid treatment does not close one particular lesion. It acts across a wider retinal area and may alter retinal pigment epithelial function, fluid transport, metabolism and local vascular signalling.
Proposed biological effects
RPE fluid transport
Laser-induced retinal pigment epithelial responses may improve the movement of fluid from the retina toward the choroid.
Cytokine modulation
Treatment may alter local inflammatory and vascular signalling, including mediators involved in retinal vascular permeability.
Reduced metabolic demand
Thermal injury to a small area of outer retina reduces local oxygen consumption and metabolic demand.
Improved oxygen diffusion
Reduced outer-retinal oxygen consumption may improve oxygen diffusion from the choroid toward the inner retinal circulation.
The relative contribution of these mechanisms remains incompletely defined. The ability of grid treatment to reduce oedema without directly closing every microaneurysm supports a biological effect beyond simple vessel occlusion. [4] [10]
Which Laser Wavelength Is Used?
The wavelength influences which ocular chromophores absorb the laser, how much the beam scatters, how well it passes through the ocular media and the depth of the resulting thermal effect.
Absorbs a broad range of retinal laser wavelengths and is the main chromophore within the retinal pigment epithelium.
Absorbs green and yellow light, making these wavelengths useful for treating retinal vascular lesions.
Absorbs blue light within the macula, which is why shorter blue wavelengths are avoided for modern macular photocoagulation.
Commonly examined retinal laser wavelengths
Argon blue-green
488 and 514 nmUsed historically, including during the ETDRS era. The 488 nm blue component is undesirable near the macula because blue light is absorbed by macular xanthophyll.
Argon green
514 nmA historical retinal photocoagulation wavelength with useful absorption by both haemoglobin and melanin.
Frequency-doubled Nd:YAG green
532 nmA commonly used modern retinal photocoagulation wavelength. It is created by frequency doubling the original 1064 nm Nd:YAG output.
Yellow laser
Approximately 561–577 nmYellow light is absorbed well by haemoglobin, is minimally absorbed by macular xanthophyll and scatters less than shorter wavelengths. It is commonly used for macular vascular treatment.
Diode near-infrared
810 nmPenetrates more deeply and has been widely used for subthreshold micropulse treatment. Subthreshold treatment is delivered without producing a visible conventional burn.
Krypton red
Approximately 647 nmA historical alternative with deeper penetration but weaker haemoglobin absorption. It is not the usual contemporary choice for focal treatment of diabetic macular oedema.
What is used for conventional macular laser today?
Green 532 nm and yellow wavelengths are commonly used for conventional focal and grid photocoagulation. Both are permitted within modified ETDRS treatment protocols.
Although their tissue-absorption characteristics differ, comparative evidence has not demonstrated a decisive clinical superiority of yellow over green laser for conventional DME photocoagulation. [4] [10] [11] [21]
Treatment Lenses and Spot-Size Correction
Macular laser requires a stable contact lens that provides high-resolution stereoscopic visualisation and accurate placement of small spots. The lens also changes the actual retinal spot size produced by the console setting.
The lens helps identify the foveal centre, retinal thickening and individual leaking lesions.
Contact with the cornea reduces unwanted movement and allows controlled placement of small laser spots.
Each model has its own laser spot magnification factor, which changes the actual retinal spot.
Common posterior-pole laser lenses
| Lens | Image magnification | Laser spot factor | Practical use |
|---|---|---|---|
| Mainster Standard Focal/Grid | Approximately 0.96× | Approximately 1.05× | Standard posterior-pole focal and grid photocoagulation. |
| Volk Area Centralis | 1.06× | 0.94× | High-resolution visualisation for focal and grid treatment. |
| Volk HR Centralis | 1.08× | 0.93× | High-resolution posterior-pole examination and laser delivery. |
| Volk Super Macula 2.2 | 1.49× | 0.67× | Very high magnification for detailed macular visualisation. |
Calculate the retinal spot—not just the console setting
Retinal spot size = console spot size × laser spot magnification factor
50 µm
Approximately 47 µm on the retina
A 50 µm console setting therefore does not automatically produce a 50 µm retinal lesion. The effect becomes more important when very small macular spots are being used.
Conventional Macular Laser Technique
Once the retinal target, wavelength and treatment lens have been selected, the next step is to decide which abnormality requires focal treatment, which area requires grid treatment, and how light the burn endpoint should be.
Confirm retinal thickening
Use clinical examination and optical coherence tomography to map the oedematous retina.
Localise focal leakage
Use fluorescein angiography when needed to identify actively leaking microaneurysms.
Identify the foveal centre
Confirm the foveal position before applying any visible macular burn.
Correct the spot size
Account for the treatment lens’s laser spot magnification factor.
A microaneurysm should not be treated merely because it fluoresces. It should correspond to an area of clinically or OCT-confirmed retinal thickening.
Focal, original grid and modified ETDRS compared
| Feature | Focal treatment | Original ETDRS grid | Modified ETDRS direct/grid |
|---|---|---|---|
| Main target | A discrete leaking microaneurysm or focal vascular lesion. | Areas of diffuse retinal thickening, leakage or capillary non-perfusion. | Relevant microaneurysms plus selected areas of diffuse thickening, leakage or non-perfusion. |
| Spot size | Approximately 50–100 µm in the original ETDRS technique; usually 50 µm in the modified protocol. | Approximately 50–200 µm. | Approximately 50 µm for direct and grid treatment. |
| Pulse duration | Approximately 0.05–0.1 seconds or 50–100 milliseconds. | Approximately 0.05–0.5 seconds. | Approximately 0.05–0.1 seconds or 50–100 milliseconds. |
| Endpoint | Whitening or darkening of the microaneurysm was historically sought; modified treatment uses a mild grey-white reaction beneath the lesion. | A more visible light-to-moderate retinal whitening was accepted historically. | A barely visible light-grey burn; visible microaneurysm colour change is not required. |
| Spacing | Each relevant focal lesion is treated separately. | Burns are separated rather than placed as a confluent sheet. | Approximately two visible burn widths between grid spots. |
| Treatment philosophy | Close the discrete leaking lesion without injuring the foveal centre. | Treat the wider area of abnormal retina using visible conventional burns. | Use small, light and selective burns rather than treating the entire macular annulus. [4] |
Treatment zones measured from the foveal centre
The treatment map is best remembered as a protected central zone surrounded by a selective treatment annulus. The whole annulus is not automatically lasered.
0–500 µm
Routine visible focal and grid burns are avoided because a scar may produce a permanent central or paracentral scotoma.
500–3000 µm
Suitable focal lesions and selected abnormal retina may be treated superiorly, nasally and inferiorly.
500–3500 µm temporally
The modified ETDRS treatment zone may extend slightly farther temporally when abnormal retina is present.
Optic-disc margin
Keep burns at least 500 µm away from the edge of the optic disc.
Papillomacular region
This is not an absolute forbidden zone in ETDRS protocols, but unnecessary treatment should be avoided. A traditional C-grid intentionally spares this region.
Historical 300–500 µm zone
Selected persistent focal lesions could historically be considered after previous treatment when vision was reduced and the perifoveal capillary network remained intact. This is not a routine modern treatment zone. [2]
Recognising the correct burn endpoint
Subtle response beneath the lesion
Aim for a mild grey-white reaction beneath the microaneurysm. A definite whitening or darkening of the lesion was sought in the older ETDRS technique but is not required in modified treatment.
Barely visible, separated burns
Modified ETDRS grid burns should be light grey, barely visible and spaced approximately two visible burn widths apart.
Dense white retinal blanching, confluent burns, explosive tissue disruption, retinal or subretinal haemorrhage, and rupture of Bruch’s membrane.
Follow-up and Retreatment
Macular laser produces a gradual anatomical response. Persistent oedema soon after treatment does not by itself mean that the laser has failed or that immediate repeat treatment is required.
Treat the selected targets
Record the treated lesions, grid distribution, wavelength, spot size, duration and endpoint.
Allow time for response
Review visual acuity, OCT and the distribution of residual thickening rather than judging treatment by an early OCT alone.
Retreatment is target-dependent
Additional laser is considered only when oedema persists and a valid, safely treatable target remains.
What should be reviewed?
Visual acuity and any change in central or paracentral symptoms.
OCT retinal thickness, fluid distribution and whether the oedema is centre-involving.
Untreated or newly leaking focal microaneurysms that correspond to persistent thickening.
Existing laser scars and the amount of untreated retina still available.
Evidence of macular ischaemia, epiretinal membrane or vitreomacular traction.
Whether observation, anti-VEGF therapy or another treatment is now more appropriate than additional laser.
When a treatable target remains
- Persistent or recurrent retinal oedema is present.
- A relevant focal lesion or selected grid-treatment area remains.
- Sufficient untreated retina is available for safe treatment.
- Additional laser is reasonably expected to provide benefit.
When more laser is unlikely to help
- The oedema is already improving.
- No valid focal or grid target remains.
- The maximum safe treatment has already been delivered.
- Centre-involving oedema is better managed pharmacologically.
- Ischaemia, traction or another mechanism better explains the visual loss.
Historical protocol timing
ETDRS and later DRCR laser protocols generally reassessed the need for further focal/grid treatment at approximately four-month intervals. An earlier review could identify an obvious missed focal lesion, but persistent oedema at six weeks was not, by itself, an indication for routine repeat laser. [2] [5]
Complications of Conventional Macular Laser
Conventional threshold laser creates a permanent thermal lesion. Complications are more likely when burns are too intense, too close to fixation, confluent or repeatedly applied to previously treated retina.
Important complications and how they arise
Central or paracentral scotoma
Why it occurs A burn is placed too close to fixation, or multiple grid scars reduce sensitivity in the paracentral retina.
Reduce the risk Identify the foveal centre accurately and avoid unnecessary visible burns within the protected central zone.
Progressive scar enlargement
Why it occurs Conventional photocoagulation scars may enlarge gradually over months or years and can extend toward fixation.
Reduce the risk Use small, light burns with adequate spacing and avoid placing threshold scars unnecessarily close to the fovea.
Reduced retinal sensitivity
Why it occurs Threshold burns damage photoreceptors within each treated spot, potentially reducing paracentral sensitivity and contrast function.
Reduce the risk Restrict treatment to clinically relevant abnormal retina and avoid dense or confluent grid patterns.
Accidental foveal photocoagulation
Why it occurs The foveal centre is misidentified, fixation is unstable, the patient moves or the aiming beam is displaced.
Reduce the risk Maintain a stable contact-lens view, confirm fixation and stop treatment immediately if alignment is lost.
Retinal or subretinal haemorrhage
Why it occurs Excessive power or prolonged exposure causes abrupt deep thermal injury and vascular disruption.
Reduce the risk Titrate power to a light endpoint and avoid rapid escalation after an initially non-visible response.
Rupture of Bruch’s membrane
Why it occurs An intense burn extends too deeply through the RPE and Bruch’s membrane.
Reduce the risk Avoid dense white, sharply cavitating or explosive burns.
Choroidal neovascularisation
Why it occurs A laser-induced defect in Bruch’s membrane can permit secondary choroidal vascular growth.
Reduce the risk Use controlled, lighter burns and investigate new haemorrhage or exudation arising at the edge of an old laser scar.
Subretinal fibrosis
Why it occurs Severe thermal injury may heal with a dense fibrotic chorioretinal scar.
Reduce the risk Avoid repeated heavy treatment in previously scarred or severely exudative retina.
Complications of treatment delivery
- Accidental foveal burn
- Dense retinal whitening
- Retinal or subretinal haemorrhage
- Rupture of Bruch’s membrane
- Immediate central or paracentral scotoma
Complications of permanent scarring
- Progressive enlargement of laser scars
- Reduced paracentral retinal sensitivity
- Chorioretinal atrophy
- Secondary choroidal neovascularisation
- Subretinal fibrosis
Newer Laser Approaches
Newer systems were developed to reduce collateral thermal injury, improve treatment precision or make spot delivery faster and more reproducible. They do not all modify the laser in the same way.
Subthreshold micropulse laser
Changes Temporal energy delivery
The exposure is divided into short ON pulses separated by OFF intervals, allowing tissue cooling between pulses. Treatment aims to produce a biological retinal pigment epithelial response without a visible conventional burn.
PASCAL pattern-scanning laser
Changes Spot pattern and pulse duration
A scanning system delivers predefined arrays of multiple short-duration spots rapidly. Its main advantages are speed, reproducible spacing and patterned delivery.
NAVILAS navigated laser
Changes Planning and targeting
Retinal imaging, digital treatment planning, image registration, tracking and computer-assisted delivery are combined to improve target localisation and treatment documentation.
Modifies the energy exposure pattern.
Modifies the speed and spatial pattern of delivery.
Modifies planning, navigation and documentation.
Subthreshold Micropulse Laser
Subthreshold micropulse laser is not simply a weaker conventional burn. It changes the temporal pattern of energy delivery so that the retina can cool between brief pulses.
Energy remains on throughout the pulse
Heat accumulates until a visible coagulative lesion is produced in the retinal pigment epithelium and adjacent outer retina.
Energy is divided into repeated pulse trains
Short ON periods are separated by longer OFF periods, reducing cumulative thermal spread.
Duty cycle
Duty cycle = ON time ÷ total pulse cycle × 100
A 5% duty cycle, for example, means that the laser is delivering energy for 5% of each cycle and is off for the remaining 95%. Commonly studied duty cycles include 5%, 10% and 15%, although protocols vary between devices and studies. [13]
Practical principles
Treatment endpoint
The exposure remains below the threshold that produces a visible retinal burn. Absence of a visible lesion is therefore an intended feature, not evidence that no energy was delivered.
Intended tissue response
The principal target is the retinal pigment epithelium. Treatment aims to modify RPE stress signalling, fluid transport and local vascular permeability while limiting photoreceptor injury.
Common wavelengths
Micropulse treatment has been delivered using 810 nm diode, 577 nm yellow and, less commonly, 532 nm green systems.
Treatment density
Because no visible scars are created, treatment is often delivered using a relatively dense or confluent pattern over the selected oedematous retina, according to the device-specific protocol.
Parameter selection
The biological effect depends on wavelength, power, duty cycle, spot size, envelope duration, treatment density and retinal pigmentation. Parameters from one platform should not be transferred directly to another.
Present clinical role
It may be considered in selected eyes for which macular laser is otherwise appropriate, particularly when reducing visible thermal scarring is desirable. It should not be presented as a universal substitute for anti-VEGF therapy.
What does the evidence show?
Micropulse versus threshold laser
In laser-suitable DME with central retinal thickness below 400 µm, 810 nm diode subthreshold micropulse treatment was clinically equivalent to standard threshold laser at two years, although slightly more laser sessions were required. [12]
Possible reduction in injection burden
A 2024 systematic review and meta-analysis found that adding subthreshold micropulse laser to anti-VEGF treatment may reduce injection burden while maintaining broadly similar visual and anatomical outcomes. The included protocols were heterogeneous, so no universal combination regimen can be assumed. [14]
PASCAL Pattern-Scanning Laser
PASCAL stands for Pattern Scan Laser. It is a laser-delivery platform that uses rapidly moving optical scanners to deliver predefined arrays of short-duration spots.
One burn with each activation
The clinician places each spot individually and determines the location and spacing of every burn.
Multiple spots delivered as a selected array
The clinician selects a predefined pattern, while the scanning system places the spots rapidly with reproducible spacing.
How pattern scanning works
Practical principles
Available patterns
Depending on the platform, patterns may include squares, grids, arcs, lines and other multi-spot configurations.
Pulse duration
Pattern-scanning treatment commonly uses approximately 10–30 millisecond exposures, shorter than the conventional 50–100 millisecond macular-laser pulse.
Thermal spread
Shorter exposure reduces lateral heat diffusion, producing a smaller and more sharply demarcated lesion.
Power requirement
A shorter pulse generally requires a higher instantaneous power to produce the same visible burn endpoint.
Treatment spacing
The platform can reproduce a selected spacing accurately, but the clinician must still choose a pattern appropriate to the retinal abnormality.
Macular use
In macular treatment, accuracy remains more important than speed. A predefined pattern should not be delivered across uninvolved retina merely because the system can generate it. [15]
Why pulse duration changes the burn
More time is available for heat to spread laterally into adjacent retinal tissue.
Less lateral heat diffusion occurs, but greater instantaneous power may be required to reach the intended endpoint.
Faster and reproducible delivery
- Rapid delivery of multiple spots
- Reproducible spacing within the selected pattern
- Shorter overall treatment time
- Reduced opportunity for movement during each array
- More sharply demarcated short-pulse lesions
Pattern delivery does not replace judgement
- The complete array must be aligned accurately before activation
- Patient movement can displace several spots together
- Short-pulse power settings cannot be copied from longer exposures
- A regular pattern may not match an irregular area of oedema
- Speed does not justify treatment of normal retina
NAVILAS Navigated Laser
NAVILAS is an image-guided retinal laser platform that combines digital treatment planning, image registration, tracking and computer-assisted delivery.
How navigated treatment works
What navigation adds
Digital treatment planning
The clinician can preselect focal targets and treatment boundaries before delivering laser.
Multimodal image correlation
Colour photography, fluorescein angiography and OCT information can be correlated to identify microaneurysms that correspond to retinal thickening or leakage.
Image registration
The digital plan is aligned with the live retinal image so that the intended target remains registered during treatment.
Eye tracking
Tracking helps compensate for small eye movements and maintain the relationship between the plan and the live fundus view.
Assisted targeting
The platform helps guide laser toward the planned retinal target, potentially improving the proportion of accurately placed spots.
Treatment documentation
Planned and delivered spots can be recorded, making later review and retreatment decisions easier.
Targeting depends on the live clinical view
The clinician mentally correlates angiographic leakage with the retinal view and places each spot using the contact-lens image.
The digital plan is registered to the retina
The selected targets are transferred to the live retinal view with image registration and tracking.
What has comparative evidence shown?
Comparative work reported a higher proportion of accurately positioned focal spots with navigated treatment than with conventional slit-lamp laser. [16]
A small comparative study reported a lower retreatment rate after navigated macular laser. This does not establish universal superiority in long-term vision. [17]
More precise planning and documentation
- Digital preselection of treatment targets
- Correlation with angiography and OCT
- Image registration and movement tracking
- Potentially more accurate focal spot placement
- Clear documentation of delivered spots
Better targeting is not the same as better vision
- The evidence base is smaller than for ETDRS or anti-VEGF therapy
- Long-term visual superiority has not been established
- Cost and availability limit routine use
- Imaging artefacts can affect target selection
- Clinical judgement is still required before every treatment
Selecting the Present-Day Approach
Treatment should follow the anatomy, visual status and retinal target—not the name of the laser platform.
Is the oedema centre-involving?
Has visual acuity been affected?
Is there a discrete, safely treatable focal leak?
Can the eye be reliably observed?
Treatment direction by clinical situation
Non-centre-involving DME with a focal leak
Focal laser Modified ETDRS Navigated targeting Consider selective treatment when the responsible microaneurysm is extrafoveal, corresponds to retinal thickening and can be treated without threatening fixation. [8] [9]
Non-centre-involving diffuse thickening
Observe Selective light grid Micropulse Mild stable oedema may be monitored. Laser may be considered when thickening is clinically significant and treatment can be delivered away from the central fovea.
Centre-involving DME with reduced vision
Anti-VEGF first Intravitreal anti-VEGF therapy is generally the principal initial treatment. Conventional macular laser should not replace it merely because focal fluorescein leakage is visible. [6] [8]
Centre-involving DME with good vision
Close observation Observation with reliable visual-acuity and OCT monitoring is reasonable when vision is good. Treatment is introduced if visual acuity worsens or the clinical situation changes. [7]
Persistent oedema during pharmacological treatment
Reassess first Adjunctive focal laser Selected micropulse Laser may be added only when a plausible and safely treatable retinal target remains after the cause of persistence has been reconsidered. [8] [10]
Before adding more laser to persistent oedema
Confirm that persistent retinal thickening still represents a laser-responsive process.
Review anti-VEGF frequency, response and adherence.
Reassess the fluid pattern and whether the centre remains involved.
Identify any relevant extrafoveal focal leak.
Determine whether macular ischaemia limits visual recovery.
Look for epiretinal membrane or vitreomacular traction.
Exclude another retinal vascular or inflammatory cause.
Macular Laser in One View
Use this final revision map to connect the historical evidence, treatment target, technique and present-day role.
Historical foundation
ETDRS established focal/grid photocoagulation for CSME and showed that its principal benefit was a reduction in further moderate visual loss. [1] [3]
Modern treatment decision
Centre involvement and visual acuity now guide treatment more directly than the older CSME label alone. [7] [8] [9]
Focal versus grid
Focal laser treats an identifiable leaking lesion. Grid laser treats a selected wider area of dysfunctional retina using separated burns.
Modified ETDRS
It remains a combined direct-and-grid protocol, but uses smaller, lighter and more selective treatment than the original ETDRS technique. [4]
Grid geometry
C-grid and ring grid describe the distribution of the grid component; they do not define a separate formal treatment protocol.
Newer approaches
Micropulse changes temporal energy delivery, PASCAL changes patterned short-pulse delivery, and NAVILAS changes planning, navigation and documentation.
Safety principle
The objective is a controlled therapeutic response, not the whitest possible burn. Treatment should remain small, light, accurately localised and restricted to valid retinal targets.
Apply What You Have Learned
Select the treatment plan that best applies the principles discussed in this companion note.
A 58-year-old patient with type 2 diabetes has a best-corrected visual acuity of 6/6. OCT shows non-centre-involving retinal thickening temporal to the fovea.
Fluorescein angiography demonstrates a cluster of leaking microaneurysms 700–900 µm temporal to the foveal centre corresponding to the area of thickening. A separate leaking microaneurysm lies 350 µm nasal to the foveal centre, without adjacent retinal thickening.
Which is the most appropriate laser plan?
Correct answer and reasoning
Correct answer: B
Laser may have a selected role in non-centre-involving DME, particularly when focal leakage corresponds to retinal thickening and can be treated safely away from the foveal centre. [8] [9]
The temporal cluster lies 700–900 µm from the foveal centre and corresponds to the area of OCT-confirmed thickening. It is therefore suitable for selective direct focal treatment.
The nasal microaneurysm should be avoided because it lies within 500 µm of the foveal centre and does not correspond to adjacent retinal thickening. Angiographic leakage alone does not make a lesion an appropriate laser target. [2] [4]
References
The clinical statements and treatment parameters in this companion note are mapped to the following guidelines, landmark trials, primary studies, reviews and official technical specifications.
-
1.
Early Treatment Diabetic Retinopathy Study Research Group. Photocoagulation for diabetic macular edema: Early Treatment Diabetic Retinopathy Study report number 1. Arch Ophthalmol. 1985;103(12):1796–1806. doi:10.1001/archopht.1985.01050120030015
-
2.
Early Treatment Diabetic Retinopathy Study Research Group. Treatment techniques and clinical guidelines for photocoagulation of diabetic macular edema: Early Treatment Diabetic Retinopathy Study report number 2. Ophthalmology. 1987;94(7):761–774. doi:10.1016/S0161-6420(87)33527-4
-
3.
Early Treatment Diabetic Retinopathy Study Research Group. Early photocoagulation for diabetic retinopathy: ETDRS report number 9. Ophthalmology. 1991;98(5 Suppl):766–785. doi:10.1016/S0161-6420(13)38011-7
-
4.
Writing Committee for the Diabetic Retinopathy Clinical Research Network. Comparison of the modified Early Treatment Diabetic Retinopathy Study and mild macular grid laser photocoagulation strategies for diabetic macular edema. Arch Ophthalmol. 2007;125(4):469–480. doi:10.1001/archopht.125.4.469
-
5.
Diabetic Retinopathy Clinical Research Network. The course of response to focal/grid photocoagulation for diabetic macular edema. Retina. 2009;29(10):1436–1443. doi:10.1097/IAE.0b013e3181bcef6b
-
6.
Elman MJ, Aiello LP, Beck RW, et al.; Diabetic Retinopathy Clinical Research Network. Randomized trial evaluating ranibizumab plus prompt or deferred laser or triamcinolone plus prompt laser for diabetic macular edema. Ophthalmology. 2010;117(6):1064–1077.e35. doi:10.1016/j.ophtha.2010.02.031
-
7.
Baker CW, Glassman AR, Beaulieu WT, et al.; DRCR Retina Network. Effect of initial management with aflibercept versus laser photocoagulation versus observation on vision loss among patients with diabetic macular edema involving the center of the macula and good visual acuity: a randomized clinical trial. JAMA. 2019;321(19):1880–1894. doi:10.1001/jama.2019.5790
-
8.
Lim JI, Kim SJ, Bailey ST, et al.; American Academy of Ophthalmology Retina/Vitreous Preferred Practice Pattern Committee. Diabetic Retinopathy Preferred Practice Pattern®. Ophthalmology. 2025;132(4):P75–P162. doi:10.1016/j.ophtha.2024.12.020
-
9.
National Institute for Health and Care Excellence. Diabetic retinopathy: management and monitoring. NICE guideline NG242. Published August 13, 2024. Official recommendations
-
10.
Everett LA, Paulus YM. Laser therapy in the treatment of diabetic retinopathy and diabetic macular edema. Curr Diab Rep. 2021;21(9):35. doi:10.1007/s11892-021-01403-6
-
11.
Yadav NK, Jayadev C, Rajendran A, Nagpal M. Recent developments in retinal lasers and delivery systems. Indian J Ophthalmol. 2014;62(1):50–54. doi:10.4103/0301-4738.126179
-
12.
Lois N, Campbell C, Waugh N, et al.; DIAMONDS Study Group. Diabetic macular edema and diode subthreshold micropulse laser: a randomized double-masked noninferiority clinical trial. Ophthalmology. 2023;130(1):14–27. doi:10.1016/j.ophtha.2022.08.012
-
13.
Sabal B, Teper S, Wylęgała EA. Subthreshold micropulse laser for diabetic macular edema: a review. J Clin Med. 2023;12(1):274. doi:10.3390/jcm12010274
-
14.
Wijeweera C, Ni J, Petocz P, Preda V, Jabbour J. Efficacy of anti-VEGF monotherapy versus anti-VEGF therapy with subthreshold micropulse laser in the management of diabetic macular oedema: a systematic review and meta-analysis. Graefes Arch Clin Exp Ophthalmol. 2024;262(9):2733–2749. doi:10.1007/s00417-024-06405-0
-
15.
Blumenkranz MS, Yellachich D, Andersen DE, Wiltberger MW, Mordaunt D, Marcellino GR, Palanker D. Semiautomated patterned scanning laser for retinal photocoagulation. Retina. 2006;26(3):370–376. doi:10.1097/00006982-200603000-00024
-
16.
Kozak I, Oster SF, Cortes MA, Dowell D, Hartmann K, Kim JS, Freeman WR. Clinical evaluation and treatment accuracy in diabetic macular edema using navigated laser photocoagulator NAVILAS. Ophthalmology. 2011;118(6):1119–1124. doi:10.1016/j.ophtha.2010.10.007
-
17.
Neubauer AS, Langer J, Liegl R, et al. Navigated macular laser decreases retreatment rate for diabetic macular edema: a comparison with conventional macular laser. Clin Ophthalmol. 2013;7:121–128. doi:10.2147/OPTH.S38559
-
18.
Striph GG, Hart WM Jr, Olk RJ. Modified grid laser photocoagulation for diabetic macular edema: the effect on the central visual field. Ophthalmology. 1988;95(12):1673–1679. doi:10.1016/S0161-6420(88)32957-X
-
19.
Ocular Instruments and Volk Optical. Manufacturer technical specifications for posterior-pole focal/grid laser lenses. Accessed July 27, 2026: Ocular Mainster Standard Focal/Grid ; Volk Area Centralis ; Volk HR Centralis ; Volk Super Macula 2.2 .
-
20.
Li HY, Guo JF, Sima J, Dai ZL. Comparison of effects of “C” and ring grid photocoagulation in the treatment of diabetic macular edema. Int Eye Sci. 2011;11(8):1344–1346. doi:10.3969/j.issn.1672-5123.2011.08.011 Used only to support historical C-grid and ring-grid terminology. It is not a current treatment guideline and does not define the modified ETDRS protocol.
-
21.
Bressler SB, Almukhtar T, Aiello LP, et al.; Diabetic Retinopathy Clinical Research Network. Green or yellow laser treatment for diabetic macular edema: exploratory assessment within the Diabetic Retinopathy Clinical Research Network. Retina. 2013;33(10):2080–2088. doi:10.1097/IAE.0b013e318295f744
