Anterior Segment Complications

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Probably the most common problem is scruffing up the corneal epithelium. Diabetics, especially by the time they have retinopathy, tend to have a bad combination of decreased corneal sensation and anterior basement membrane abnormalities. This can predispose them to punctate epithelial erosions or even full-thickness epithelial defects from the use of the contact lens. Fortunately, this is not very common, and if there are symptoms they tend to be mild and self-limited—meaning that they are a perfect indication for all those artificial tear samples that keep building up in your cabinets. It also helps to rinse out the methylcellulose after treatment, both to increase the patient's comfort and because sometimes the methylcellulose can thicken and make the eye very irritated once the topical anesthetic has worn off. Don't forget to remind the patient to avoid rubbing their eye while it is numb, as well. If there are a lot of pre-existing anterior basement membrane changes, or if the patient has a history of getting a full thickness epithelial defect after a laser, you will want to be very careful with their epithelium. You can consider adding copious ointment to the eye or even patching it temporarily to protect the epithelium while the anesthetic wears off.

Really fragile corneas may need "no touch" techniques, such as using a 90-diopter lens to deliver the laser without using a contact lens. It is a bit of a hassle because you don't have as much control over the eye and you have to keep the lids open with your other fingers, but it is a technique that comes in handy at times. It has also been suggested that you can use a bandage contact lens underneath your laser contact lens if necessary.2 Another option would be to deliver the laser using an indirect ophthalmoscope—although most general ophthalmologist's offices do not have one of these. If you are interested in doing this, there is an excellent reference at the end of Chapter 14.

Occasional patients may even have surface problems with the fellow eye. These patients are so busy trying to keep their fellow eye open and to fixate properly that they can actually dry it out, creating a lot of post-laser pain in an eye you never touched. Always encourage patients to periodically close their fixating eye, so as not to run into this problem. (By the way, this is particularly likely if you are treating both eyes at the same session. If they keep the eye you first treated wide open while you treat the second eye, they can really dry out the cornea because they are numb—especially if any methylcellulose is holding the anesthetic on the epithelium. You definitely need to remind them to close their first eye in this situation.)

It is also possible to cause corneal or lens burns with the laser, especially if you are using high powers. As mentioned in the chapter on contact lenses, the wide-field indirect lenses can actually result in high irradiance at the plane of the cornea or lens, especially with very large spot sizes. This becomes important if there are any opacities that might take up the laser on its way to the retina— such as eyelashes or bits of mascara stuck under the contact lens, or corneal pigmentation near the limbus.

A problem that was more common in the past was the occurrence of burns in the lens. This would happen if there was significant nuclear sclerosis: The yellowed lens would take up the laser (especially the blue-green wavelength that was more common back then). Patients would end up with very characteristic lenticular burns (see Figure 1).

Figure 1. Lens burns seen with the red reflex and up close with direct illumination. With conservative powers and spot sizes, you will likely never see this, but be careful if you are using an indirect contact lens with large powers and spot sizes of 500 microns or more.

Other anterior segment complications include iatrogenic Aide's pupil, which can result from very heavy laser, especially anterior to the equator where the short ciliary nerves branch out to reach the ciliary body and iris. This probably will not have any significant visual consequences, but patients may get very fussy if they feel you have changed their appearance—not everyone wants to look like David Bowie. Basically, try not to use deep and heavy burns unless absolutely necessary, when treating over the long ciliary nerves in the horizontal meridian or when treating anterior to the equator.

You can bet that if your laser can affect iris function, it can also affect ciliary body function—and this can be far more annoying. A heavy PRP can definitely decrease accommodation. This is particularly important in a patient who is in the pre-presbyopic or early presbyopic age range. Remember that diabetics can have autonomic neuropathy to begin with, and if you tip them

Lenticular Sclerosis Red Reflex

Figure 1. Lens burns seen with the red reflex and up close with direct illumination. With conservative powers and spot sizes, you will likely never see this, but be careful if you are using an indirect contact lens with large powers and spot sizes of 500 microns or more.

Figure 2. David Bowie's eyes.

into more pronounced presbyopia, you can end up with a very unhappy patient, even if your superb laser has spared them from total blindness. Again, you have to do what you have to do, but it is important to both warn patients about this possibility so they are not surprised, and to try to go easy when treating over the nerves if possible.

There are also patients that can develop rather severe iritis after a laser. This is more likely with hot and heavy treatment, and sometimes it can even result in synechia formation—something to be avoided in patients that need to be dilated a lot to see the back of their eye. (Synechia can also occur of you are clipping the pupil margin with your treatment. This is more likely with an indirect ophthalmoscope delivery system, but it can happen with a slit lamp laser, too.) Consider using a topical steroid and cycloplegic if you put in a lot of laser or if you have a patient with a history of uveitis.

Patients can also have problems related to elevated intraocular pressure. Heavy panretinal photocoagulation can cause diminished outflow because of swelling of the ciliary body. Occasionally this swelling can even rotate the iris enough to cause angle-closure glaucoma. This is more likely in patients who already have narrow angles, and you may want to avoid very heavy treatment in one session with such patients. This is also something to keep in mind if you have a patient with longstanding glaucoma and fragile nerves. Even if they don't get angle closure they can have a transient rise in pressure that can threaten their nerve, and you should adjust your treatment accordingly.

The important thing is that if a patient calls you because of pain subsequent to panretinal photocoagulation, do not assume that they are a wimp and phone in some narcotics. You really should look at them to determine if they have developed uveitis, elevated pressure or even angle closure. By the way, these problems tended to be more common in the old days when patients were pounded with confluent white-hot laser burns or, worse, were treated with xenon photocoagulation. Doing a gradual, careful PRP is much less likely to result in problems, but it is still important to be aware of all the trouble you can cause.

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