Harry W Flynn, Jr, MD
Recognition of severe nonproliferative diabetic retinopathy (NPDR) is crucial to timely treatment. The Early Treatment Diabetic Retinopathy Study (ETDRS) used an elaborate scale to grade retinopathy severity from 0 to 99, with higher numbers indicating more severe grades of retinopathy. Wilkinson has developed a simplified severity scale, the International Diabetic Retinopathy Disease Severity Scale, and proposed the “4:2:1 rule” for diagnosing severe NPDR. The 4:2:1 rule states that severe NPDR exists if severe hemorrhages are present in all 4 quadrants of the retina, or venous beading exists in 2 or more quadrants, or moderate intraretinal microaneurysms exist in 1 or more quadrants. Severe NPDR diagnosed by the 4:2:1 rule corresponds to an ETDRS severity of 53. Patients with severe NPDR have a 1-year risk of progression to proliferative diabetic retinopathy (PDR) of 20%. Patients with 2 or 3 of the conditions in the 4:2:1 rule have very severe NPDR, and a 1-year risk of progression to PDR of 40%. Panretinal photocoagulation (PRP) should be considered for patients with very severe NPDR, as it would be for patients with extensive neovascularization.
The Diabetic Retinopathy Study (DRS) established the value of PRP for PDR, but used much more intense laser burns than the current standard of care. The DRS treatment criteria called for a 500-micron spot size of 0.2 sec duration beginning at 250 milliwatts power and adding 50 milliwatt increments until a characteristic gray-white burn was attained. A green argon laser should be used unless vitreous hemorrhage or cataracts are present, in which case the red wavelength can be used. Dr Flynn recommended a burn duration of 0.05-0.1 seconds at 200-700 milliwatts until a yellow-white burn is attained. He cautioned that chalk-white, heavy burns can cause choroidal bleeding and should be avoided. He recommended placing 1200-1600 spots in 2 treatment sessions to avoid choroidal glaucoma. In each session, a uniform pattern of burns should be laid down from 1 disc diameter nasal to the disc to 2-3 disc diameters temporal to the fovea up to the equator. Burns should be spaced ½ burn width apart. Dr Flynn mentioned that the Pascal laser, which permits patterns of multiple less-intense burns to be deposited with a single press of a footswitch, was a quicker, more tolerable procedure for patients than conventional laser therapy. Large numbers of burns (eg, 4000-5000) should not be used, because they become confluent 3-5 years post-PRP. Dr Flynn does not routinely administer anesthetic to patients undergoing laser treatment, but he will give a regional block to patients who must undergo laser indirect ophthalmoscopy (LIO) due to the presence of cataract. Most patients find LIO intolerably painful without anesthetic.
In the case of recurrent vitreous hemorrhage, either additional PRP or vitrectomy may be considered. Dr Flynn recommends filling in PRP prior to considering vitrectomy. The Diabetic Retinopathy Vitrectomy Study (DRVS) showed that early vitrectomy is most beneficial in patients with type 1 diabetes. Vitrectomy is indicated in the following situations:
- Nonclearing vitreous hemorrhage
- Tractional macular retinal detachment
- Trational rhegmatogenous retinal detachment
- Iris neovascularization with opaque media
- Macula obscured by opaque fibrovascular membranes
- Extensive active neovascular or fibrovascular proliferations (per DRVS)
- Progressive macular traction
- Macular edema with posterior hyaloid traction
Currently, there is a great deal of interest in using pharmacologic vascular endothelial growth factor (VEGF) inhibitors in the treatment of diabetic retinopathy. The Diabetic Retinopathy Clinical Research network is conducting a prospective, randomized, controlled trial of ranibizumab as a treatment for diabetic retinopathy; the trial is funded by the drug’s manufacturer. A VEGF inhibitor might be used in the following situations:
- In conjunction with PRP for neovascular glaucoma with active neovascularization in the angle
- Prior to vitrectomy for anterior segment neovascularization with dense vitreous hemorrhage
- Prior to vitrectomy for very severe and active PDR with traction retinal detachment
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