In Laser Therapy, Less is More
Current procedures can generate greater scarring
Laser treatment (known as photocoagulation) has become the ‘gold standard' for preventing and minimizing vision loss from sight threatening diabetic retinopathy. Photocoagulation refers to the precise and concentrated application of high energy light, typically of a single wavelength or color (called monochromatic light). This light energy (photo-) is absorbed by body tissue and generates heat, which, in turn, causes clotting (-coagulation) of blood and localized, thermal destruction of that tissue. When applied to the retina, the light-sensitive membrane lining the inside back wall of the eye, laser energy creates focal "burns" that have two principal effects: (1) they destroy small areas of the retina and (2) they seal off damaged, leaking blood vessels that threaten vision.
Retinal photocoagulation benefits patients with diabetic macular edema (DME) by minimizing fluid leakage from damaged blood vessels within the macula, the center of the retina responsible for detail and color vision, essentially by cauterizing those leaky vessels and/or promoting release of naturally occurring, protective biochemicals. Laser therapy of the peripheral retina (known as panretinal photocoagulation or PRP) also causes regression (shrinkage) of the abnormal blood vessels found in proliferative diabetic retinopathy (PDR). It is thought that sacrificing some of the peripheral retina, by destroying it with laser burns, turns off the chemical messengers causing abnormal blood vessel proliferation, thereby protecting the macula and overall vision from more severe injury due to bleeding and scar tissue formation.
Unfortunately, current laser therapy is inherently destructive to the retina, creating a good deal of heat (thermal damage) and leaving visible treatment scars that affect vision. About 1 in 10 patients lose some vision on the eye chart as a result of treatment. It often reduces a patient's night vision or his/her ability to function well when going from a lighted environment to a darkened one (e.g., a movie theater). It often causes a loss of peripheral vision or abnormal blind spots in a person's central vision, depending upon where the laser burns are placed. Loss of side vision can make it difficult to navigate in a crowded environment, like a busy street. Missing areas of central vision can make it difficult to efficiently read words on a page or accurately perceive color. Photocoagulation can also result in a loss of ability to change focus from distance objects to near objects. The heat generated by the laser can also cause significant pain during treatment, especially in younger patients. The laser burns themselves occasionally can become a site for the development of scar tissue or abnormal blood vessel growth beneath the retina, leading to vision loss.
Recently, a new type of photocoagulation procedure - using less energy and less exposure time to each laser ‘burn' - has been pioneered by a retinal specialist in California to successfully treat both macular edema and proliferative retinopathy in patients with type 1 and type 2 diabetes. The lower energy (less powerful) laser applications are pulsed (divided up into a series much briefer applications), resulting in less heat. This technique, called subthreshold diode micropulse (SDM) photocoagulation, results in no visible laser treatment scars and may improve visual functioning (see figures 1-4 below). In one study, SDM PRP treatment resulted in no patient complaints of pain, loss of focusing ability, or loss of peripheral vision or night vision; the treatment was successful in more than 85% of cases – very comparable to results achieved with standard laser protocols. In another study of SDM for treating diabetic macular edema, visible scars and post-treatment complications were totally prevented, though patients with more severe DME generally did not benefit as much from treatment.
Clinical protocols for SDM photocoagulation will undoubtedly evolve as more research is conducted. Conventional photocoagulation has saved thousands of patients from severe vision loss and blindness, as it did for me almost 25 years ago. However, it does leave the retina looking a bit like a battlefield and very often compromises vision. In tandem with newer medical therapies for sight-threatening diabetic retinopathy (see my previous column titled Management of Diabetic Retinopathy in the 21st Century), SDM may bring us closer to the goal of successfully treating severe retinopathy without leaving the retina looking like a ‘battlefield' and with no effect on patients' quality of life.
Luttrull JK, Spink CJ, Musch DA, : Subthreshold diode micropulse panretinal photocoagulation for proliferative diabetic retinopathy. Eye, 2007 Feb [Epub ahead of print] PMID 17293791; Print pub Eye 2008; 22: 607-612.
Luttrull JK, Musch MC, Mainster MA: Subthreshold diode micropulse photocoagulation for the treatment of clinically significant diabetic macular edema. Br J Ophthalmol 2005 89:1; 74-80.
Luttrull, JK. Atraumatic photocoagulation for retinovascular disease. Case studies of micropulsed 810 nm diode laser photocoagulation in the management of diabetic retinopathy. Retinal Physician, 2005;2: 65-87.
Shimura M, Yasuda K, Nakazawa T, Tamai M. Visual dysfunction after panretinal photocoagulation in patients with severe diabetic retinopathy and good vision. Am J
Ophthalmol 2005; 140: 8–15.
Laursen ML, Moeller F, Sander B, Sjoelie AK. Subthreshold micropulse diode laser treatment in diabetic macular oedema. Br J Ophthalmol 2004; 88: 1173–1179.
For more information on diabetic eye disease, consult Dr. Chous' book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.
Read more about Dr. Chous here.
Visit Dr. Chous' website here.
NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.
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