After having carefully reviewed all the different ways you can screw up with lasers, it is important to remember that perhaps one of the most worrisome complications is to have your treatment fail because it was inadequate. Generally, a "less is more" technique is the best way to go, because the fewer spots you need to place—for any treatment—the more vision your patient gets to keep. Unfortunately, if you don't put in enough spots to control the disease, then you for sure haven't done the patient any favors. Decisions about how aggressive to be will become easier with time and experience, but remember, if you do end up going light with any laser, watch the patient closely and do not allow them to be lost to follow up for any reason.
1. Fong DS, Girach A, Boney A. Visual side effects of successful scatter laser photocoagulation surgery for proliferative diabetic retinopathy: a literature review. Retina 2007;27:816-24.
2. Folk JC, Pulido JS. Laser photocoagulation of the retina and choroid. San Francisco: American Academy of Ophthalmology, 1997.
Singerman LJ, Coscas GJ. Current techniques in ophthalmic laser surgery, 3rd ed. Boston: Butterworth-Heineman, 1999.
L'Esperance FA. Ophthalmic lasers, 3rd ed. St. Louis: Mosby, 1989.
Bloom, SM, Brucker, AJ. Laser Surgery of the Posterior Segment. Philadelphia: Lippincott Williams & Wilkins, 1997.
Davis MD, Blodi BA. Proliferative Diabetic Retinopathy. In: Ryan SJ. Retina, 4th ed. Philadelphia: Elsevier Mosby, 2006:v.2, pp 1285-1322.
Blondeau P, Pavan PR, Phelps CD. Acute pressure elevation following panretinal photocoagulation. Arch Ophthalmol 1981;99:1239-41.
One of the most difficult aspects of treating proliferative diabetic retinopathy is deciding whether further treatment is warranted. About two thirds to three fourths of treated eyes will demonstrate regression, and sometimes this can begin as early as a few days after treatment. It usually takes a bit longer to see the full effect of the laser, so it is common to check patients at about six to eight weeks after the last laser session to get a sense their response. If there is a potential for significant traction or if the patient is particularly worrisome, it makes sense to see them sooner.
The ideal response is complete resolution of the neovascularization, period. Unfortunately, this ideal is not as common as one would wish, especially in younger patients, and often there are persistent vessels of some sort. If there is any sense that the vessels are growing, or if there is evidence of vitreous hem-orrhaging (even small amounts of blood in the far periphery that are otherwise asymptomatic), then it is very reasonable to put in more laser. Although there are no controlled studies defining the amount of laser, there is a sense that if the first treatment does not work, a rather substantial amount of laser is necessary to generate any sort of useful response the second time around. For instance, it probably does not help to put in 200 to 300 spots in a patient with persistent disease—instead, it seems that such patients usually need an additional critical mass of perhaps 500 to 1,000 spots.1 The exception to this would be if there is an area of the fundus that has less treatment, and especially if the new vessels are clearly growing in the direction of the untreated area. In this case, a smaller amount of treatment directed to the ischemic area may be all you need.
As mentioned before, you can squeeze in over 6,000 spots to control the disease, but such patients may benefit from referral for intravitreal therapy and/or a vitrectomy, rather than dribbling in more and more laser over several months and slowly eliminating all their visual field. The vitreous does seem to play a role in stimulating the blood vessels, and by having it removed patients may get by with much less laser. Chapter 18 discusses when to consider referral in more depth.
If the blood vessels seem to have shrunk back somewhat, but have not disappeared, the decision to treat can be more difficult. Some patients may simply have persistent neovascularization that doesn't cause trouble for years, and for these patients additional laser is a waste of time and peripheral vision. If the residual vessels are small in size and have really shrunk down in caliber, and if they are not widespread, it makes sense to watch them a bit. Another pattern that suggests quiescence is if the tips of the vessels have receded into thick, clublike endings.
If the vessels are becoming more fibrotic in nature it suggests that the retinopathy is leaving the proliferative phase and laser may not be needed (but do watch for progressive traction). On the other hand, if the tips of the vessels consist of fine, sprouting buds, then treatment should be added. Sometimes a fluorescein angiogram can be helpful—active vessels can be very leaky, whereas quiescent, involuted vessels will leak much less.
Figure 1. Old and new neovascularization. The photo on the left shows the kind of thready, ropy appearance of regressed neo after PRP. Note the clumpy, grapelike appearance of the ends of the vessels; they have shriveled up in failure. The photo on the right shows active vessels. Note how they are spread out and arborized, with fine vessels at the tips growing in all directions. Also note that the image on the left was Photoshop'd to make the vessels easier to see. (Right photo courtesy of the Early Treatment Diabetic Retinopathy Study Group)
Figure 2. Another example of regressed neovascularization, showing the shriveled appearance of the old vessels. Note the relative lack of staining in the later phases of the angiogram (middle). Such vessels are often nicely backlit by the small amount of fluorescein that does leak out. Compare this to the figure on the right, which shows the florid leakage seen with new, active vessels: There is no view whatsoever of the actual vessels themselves, because they are obscured by all the fluorescence.
Another important variable is the density of your PRP. If you were trying to go lightly and the vessels don't seem to be regressing, then you should consider filling in the PRP pattern. An angiogram may be helpful here because it may demonstrate areas of non-perfusion that are not obvious clinically and you can see whether your initial laser covered such areas.
If you do decide to add treatment, you can fill in between spots and extend your treatment further into the periphery. You can also extend the treatment closer to the center of the macula, but if you really think you need to laser valuable real estate, you may want to get a second opinion beforehand. Also, if you need to treat over previously treated retina you need to be very careful about where you place your spots. Treatment that hits previous laser scars may be painful for the patient, and more importantly, the cicatricial pigmentation can dramatically increase the laser uptake and cause a hemorrhage or hole.
Other factors that may help you decide about how hard to treat residual vessels were discussed in preceding chapters. They include the patient's age, the course of the fellow eye, the degree of compliance and control, and whether the patient is on Coumadin.
A conundrum that occasionally comes up is when a patient had the first stage of a PRP performed, but either never returned for follow up or the treating physician was happy with the initial results and did no further treatment. You may see these patients years later with partially treated neovascularization, no symptoms, and laser treatment in only one sector of the fundus. If they have been stable for quite some time, and if they have good systemic control, it is reasonable to observe them. There is a risk of progression of their proliferative disease if they are left untreated, but there is also a risk of converting a happy asymptomatic patient into a bitterly symptomatic patient from problems related to a full dose of PRP. You just have to use your clinical judgment, and if the patient does elect observation it is important that they understand the risks and the need for continuous follow up.
The converse occurs when a previously untreated patient needs treatment and has only a single clump of neovascularization in one part of the fundus.* It may seem that doing laser in only that area is all that is needed. This is not a good idea. A localized area of neovascularization does not mean that only one part of the retina is ischemic; there are no secret barricades to vasopro-liferative substances in the eye. You may be able to get away with a milder PRP in such a patient, but once a patient crosses the line into needing laser, it is a good idea to treat all around the fundus rather than in one local area.
*By the way, make sure you have the correct diagnosis in such a patient. For instance, they could have the entity mentioned in Chapter 26 that begins with a "B."
It turns out that in addition to figuring out how to manage residual neovascu-larization, there can also be problems deciding what to do about patients who have recurrent vitreous hemorrhages. It turns out that it is not uncommon for diabetics with persistent neovascularization to have intermittent hemorrhages over the years. If the vessels are growing or appear succulent, and there are significant areas of untreated retina, then adding more PRP is the simplest thing to do.
Sometimes, however, hemorrhages may be due to intrinsic vascular fragility; an eye that is full of beat-up old blood vessels will have an occasional spontaneous hemorrhage, just like people can have spontaneous bruises on their legs. More laser is unlikely to make any difference in such patients, and if you feel their proliferative disease is burned out and their PRP pattern is adequate, then observation is all that is needed.
A more common problem is age-related vitreous contraction beginning to tug at old neovascularization. In fact, patients may go years with nicely controlled disease, and then suddenly start to get hemorrhages simply because they have survived long enough for their vitreous to shrink and start pulling on the regressed vessels. Adding more laser may be irrelevant for such patients, because now a mechanical problem is being imposed on their otherwise quiescent prolif-erative disease. On the other hand, it may be reasonable to fill in with more laser if there are large areas of untreated retina in the periphery (the assumption would be that vasoproliferative factors released by the untreated retina are keeping the vessels a bit more swollen than they might otherwise be, and they are therefore more likely to hemorrhage with even a little traction). Usually, however, such patients will need a vitrectomy if the hemorrhages are recurrent and do not clear quickly.
A variation on this theme is if the patient begins to develop vitreous contraction, and then is fortunate enough to get a complete vitreous separation from the retina. If this happens, patients almost always get a vitreous hemorrhage, but the process also eliminates all the traction. These patients may have very little in the way of subsequent hemorrhaging, and there is no role for more laser.
And once again: Although complete vitreous separation is usually a cause for celebration in the setting of diabetic retinopathy, don't forget to look carefully for retinal breaks or tears.
However, a total vitreous detachment is a lucky event that does not happen too often; usually the vitreous is only partially separated, and it then applies even greater traction wherever it remains attached. If there are areas where the PRP pattern is light, then more laser may help to shrink down the vessels that are now being tugged on more aggressively. Usually a vitrectomy is required if the hemorrhaging is persistent.
If there is one patch of neovascularization that keeps bleeding in spite of good laser, some doctors advocate attempting to directly close the offending vessels with focal laser. This may be something to try if the vessels are small and flat and the retina is relatively healthy—but this is something that is much easier said than done even in the best of circumstances. If the vessels are big or elevated, or if the retina is thin and on stretch, you can end up creating a hole which will cause a detachment. This is a big disaster. If you really want to try this technique, consider getting some help before you do—nowadays a vitrectomy is probably safer.
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Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...