Posterior Segment

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Most posterior segment issues have already been discussed in the preceding chapters—but a little repetition is good, because you want to make it through your whole career without gaining personal experience with any of these problems.

Perhaps the most disastrous mistake is to create an inadvertent foveal burn. Follow all the advice about constantly checking your location in the fundus and always know for sure where you are. Remember that you are far more likely to do something like this when you start to feel very comfortable with your laser skills, and that it is especially likely to occur when you are frantically trying to stay above water on a busy clinic day. Don't ever get overconfident, and don't ever let yourself feel rushed when you are guiding coherent light into a fellow human being's eye. You don't want your handiwork to turn into a treasured slide in some retina specialist's talk on laser complications.

If you forget which eye you are treating, or if you mix up which side of the eye you are treating while using an indirect lens, you can easily get lost. This is especially likely when treating in the temporal aspect of the posterior pole, where there is no optic disc or vascular arcade to warn you that you are crossing into no man's land. This can happen more readily if your view is limited by a small pupil, or if media opacities interfere with your ability to sweep around and orient yourself. Also, remember that if you are using the large mirror in a Goldmann three mirror lens, it is possible to get deep into the macula without realizing it, especially if the patient is looking toward this mirror (Figure 3 in Chapter 4). Sometimes patients will have large vessels running across the posterior pole that can simulate the appearance of nasal retina, and this can really confuse you if you are not careful. If you come across such a patient, be very careful about where you are treating.

Almost all of these problems can be overcome by simply checking where you are at all times so that you do not get a chance to get lost. As mentioned before, it is good to set landmarks in your head so that if you see them, you know you are in a danger zone. Another option, especially when performing PRPs, is to put a line of laser spots at the posterior edge of your planned treatment pattern and then treat outward from this line—always moving from the back of the eye to the front—so at all times you are moving away from the posterior pole as you place spots.

Figure 4. (Right) This should make your primary sexual organs shrivel. But you can see how easy it could be to do this, given the hazy view, the hemorrhage that obscures retinal vessels and the nearby laser scars. All of these things can make you think you are where you are not.

Figure 3. (Left) Whew, just in time. Five out of five doctors recommend not putting your PRP here...

Figure 3. (Left) Whew, just in time. Five out of five doctors recommend not putting your PRP here...

Figure 4. (Right) This should make your primary sexual organs shrivel. But you can see how easy it could be to do this, given the hazy view, the hemorrhage that obscures retinal vessels and the nearby laser scars. All of these things can make you think you are where you are not.

There are also a host of complications related to poor power management with your spot size and intensity. If you remember all of the variables that can get you into trouble, you can stay out of trouble. For instance, if you decrease the spot size, or if your aiming beam suddenly becomes smaller and brighter, you know you need to cut back on the power.

The point is that a hot spot can cause any number of problems, all of which are bad. A hot spot can cause a vitreous hemorrhage, intraretinal hemorrhage, subretinal hemorrhage, and even choroidal hemorrhage if you manage to burn down deeply. Remember, too, that if you have actually done any of these things, then you should keep pressure on the eye with the contact lens until any bleeding stops. Also remember that if you burned something bad enough to cause a hemorrhage, you have probably also created a full-thickness retinal hole. You want to make sure you treat around the offending area enough to tack the retina down so you don't get a detachment.

A severe burn in the peripheral retina can also result in a late complication known as a choroidal-vitreal anastamosis. In this case a hot burn gets so deep that choroidal vessels are induced to anastamose with retinal vessels and then the ensuing network grows up into the vitreous, creating very aggressive, destructive neovascularization. This problem was more likely in the bad old days, and often occurred when people were using very heavy treatment with laser or xenon arc in an attempt to directly shut down NVE. This is something that is useful to know about in the abstract, but you should never come close to causing it.

You can also poke holes in things without a hemorrhage, and this is particularly noticeable if you burn through Bruch's membrane while doing a focal. The sickening sight and sound of this, as mentioned in Chapter 8, is something you should strive to never experience. If it does happen, remember that such a spot may be nidus for development of a choroidal neovascular membrane, and you will want to watch for any unusual subretinal hemorrhage or localized macular edema that heralds the development of such a problem. Also, recall that you do not necessarily have to break Bruch's membrane to get a neovascular membrane; it can also occur around less intense laser treatment. All of this is why you should strive to do the least amount of laser necessary to treat macular edema.

Also remember that there are occasional patients who are extremely good observers and will notice each and every focal spot that you apply. These are more likely to be younger, type-A patients who do not have a lot of diabetic disease and who are much more likely to notice the punctate changes in their paramacu-lar vision. As mentioned in the chapter on informed consent for treating diabetic macular edema, you want to make sure patients are aware of this possibility and you should always treat as lightly as you can—but if they need treatment, they need treatment.

There are also a few things that can happen when treating proliferative disease that are not really complications, but your patient may be likely to feel that they are—for instance, the occurrence of a vitreous hemorrhage shortly after a PRP due to the shrinkage of the blood vessels. There is really no way to avoid this, and it may actually represent a good response to treatment. However, you do need to warn the patient about this possibility, especially if they are presenting with asymptomatic proliferative disease.

The other "complication" is that the patient may develop more significant traction, perhaps even a retinal detachment, as the neovascular tissue responds to your treatment. If you think something like this might happen you want to be very clear about this prior to treatment, especially in patients who are presenting late in their proliferative career with extensive disease that should never have been allowed to develop in the first place. If you are worried that this could be a big problem, you might want to refer the patient to your friendly neighborhood retina specialist.

Sometimes a very aggressive PRP can result in an exudative retinal detachment and/or choroidal effusions, which can even simulate a rhegmatogenous retinal detachment. Usually, this problem is evidence of a very sick eye, and it is more likely to occur in patients who get lots of hot spots in one sitting. If you actually manage to do something like this to a patient, you should give them topical steroids and cycloplegics to help things settle down, and then try to be gentle with any additional treatment.

Figure 5. Intense PRP resulting in a peripheral serous retinal detachment. (Figures 1, 3 and 4 courtesy of James C. Folk, M.D. [the images—not the techniques])

There are other, stranger things that have been reported. For instance, patients have developed thermal optic neuritis from excessive treatment near the nerve, or retinal vasculitis and even vascular occlusion from hot burns on vessels. You should never, ever have any experience with entities such as this; they are included simply for completeness.

A more common problem associated with panretinal photocoagulation is peripheral field loss, and this was especially likely in the olden days when large amounts of laser were applied rapidly. Measurable changes can occur in up to 50% of patients, although milder treatment seems to have less of an effect.1 Of course, patients are receiving the treatment in the first place because the bulk of their peripheral retina is either dead or dying off—the difference being that if they choose to have field loss from their disease alone, they have to accept the risk of total vision loss from untreated retinopathy. In other words, whether peripheral field loss is related to the disease or your treatment is largely academic; the patient really has no choice. Hopefully you, with your newly gleaned knowledge, will be able to put in a gentle yet effective PRP with less risk of dramatic visual field loss than was seen in the old days. Still, this can be a real problem—espe-cially in terms of driving—and hopefully a time will come when patients won't have to risk this additional insult to their vision as new pharmacologic treatments come online.

Panretinal photocoagulation can also cause problems with dark adaptation, nyctalopia and color vision, all of which seem more likely with heavier treatments. However, it is hard to know to what degree these can be attributed to the laser versus the severity of the underlying retinopathy. Even diabetics who do not need PRP complain of problems along these lines as they get older and experience the general deterioration of retinal function that occurs with the disease. Nevertheless, if significant problems occur right after a laser, then it probably was the laser and patients need to be warned about this possibility.

A related problem is the fact that many diabetics will complain of increased sensitivity to light. Again, this may represent overall generalized deterioration due to diabetes. However, it is also likely that the loss of peripheral pigmentation that accompanies extensive scarring from laser treatment allows light to bounce around in the eye, so that the remaining compromised retina has even more problems in bright light situations.

Of course, one of the main complications of both macular treatment and PRP is decreased central visual acuity. This is usually due to exacerbation of preexisting macular edema, and ways to avoid this are specifically covered in the chapters on performing these treatments.

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