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Is Pattern Laser better for Diabetic Retinopathy than conventional way of laser?



In a recent retrospective study from Turkey, the researchers compared conventional panretinal photocoagulation (PRP) versus pattern scan laser treatment to evlauate outcomes including central macular thickness (CMT) and retinal nerve fibre layer (RNFL) thickness before and after the treatment in 57 patients.



In the conventional laser group, PRP was completed using the LightMed LightLas 532 laser device in accordance with the ETDRS protocol. In the pattern laser group, it was completed in a single session using PASCAL device with 20 ms pulse duration and multispot pattern. Central macular thickness (CMT) and retinal nerve fiber layer (RNFL) thickness were evaluated before laser treatment and at 1, 6 and 12 months after treatment.


In both groups, CMT increased significantly (p<0.001), while RNFL thickness decreased significantly (p<0.001) at 12 months. While CMT and mean RNFL thickness increased in the first month in both groups, it decreased progressively until the 12th month. This change is observed more in the conventional laser group compared to the pattern laser.


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Panretinal Photogoagulation (PRP) has been a mainstay for treatment of proliferative diabetic retinopathy (PDR) for many decades. Since the time a xenon arc laser was developed in the 1950s by the Carl Zeiss Laboratory, laser photocoagulation has been used clinically in treating many retinal diseases. Later, when argon laser was discovered to be useful as well, the Diabetic Retinopathy Study (DRS) was initiated to determine whether photocoagulation helps prevent severe visual loss from proliferative diabetic retinopathy, as well as to determine whether a difference exists in the efficacy and safety of argon versus xenon photocoagulation for proliferative diabetic retinopathy.


The study showed that that laser therapy was indeed beneficial to patients with PDR and also showed that argon lasers created less adverse effects for patients than xenon lasers while retaining similar efficacy.


Since then, laser photocoagulation or PRP has become the mainstay of treatment for PDR. The procedure involves creating thermal burns in the peripheral retina leading to tissue coagulation, the overall consequence of which is improved retinal oxygenation. While highly effective, there have been concerns historically regarding the anatomic effects and visual complications following PRP, the most common of which include choroidal effusions, exudative retinal detachments, macular edema, visual field deficits, and night vision defects.


To avoid the damage to the retina due to laser, and its corresponding effects, anti-VEGF injections have been evaluated as a form of treatment. As DRCR protocol S showed, anti-VEGF drug ranibizumab was found to be noninferior to PRP in managing patients with PDR. But as is the case with anti-VEGF injections, retina specialists take the decision based on the likelihood of patient compliance and reliability, since multiple anti-VEGF injections are likely required, and if the patient is not compliant, and gets delayed in the suggested frequency, the disease may progress enough to require a surgery. Also, the injections do not appear to permanently address neovascularization. Which is why retina specialists continue to use PRP as a modality of treatment for PDR. Most consider a hybrid approach, with anti-VEGF injections initially followed by PRP if PDR does not appear to stabilize with injections alone. The injections also help to reduce vascularity before the laser can be applied, or in cases where the view is not clear at all for laser to be advised, or before a surgical intervention.


So what is the algorithm for PRP vs anti-VEGF injections in patients with PDR?


For patients who are likely to stay compliant, in relation to Lucentis injections, DRCR Protocol S suggests the following:

  1. 6 monthly injections starting at baseline unless retinal neovascularization (NV) resolves completely at 4 or 5 months.

  2. After the initial 6 months, if NV was stable over 2 consecutive visits, injections can be deferred.

  3. If NV worsens subsequently, anti-VEGF treatment should be resumed.

  4. PRP could be initiated for failure or futility criteria.


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