Iscellaneous

Lasering in the Infrared

Odds & Ends

Infrared diode lasers tend to be cheaper and relatively bulletproof (their design is simpler than a frequency-doubled green diode laser and they require way less fuss than a gas laser). If cost or logistical considerations are important, you may have no choice but to use infrared. This could be problematic because infrared is much trickier to use. Appendix I talks a bit about the special needs of learning this wavelength—best to carve through the basic techniques covered in this book, and then you can read the stuff in the appendix to get ready to use infrared.

Micropulse and Other "No Touch" Lasers

There are lots of wondrous things to be found in the halls of diabetic retinopathy treatment. This might be one of them. Not a common technique, micropulse laser involves delivering only a fraction of the requested power over the duration of a burn. It does this by delivering laser energy in pulses rather than continuously, and it brings into the mix a cool new term: duty cycle. This is simply the percentage of time that the pulses are actually delivering laser power relative to the total time of the exposure (Figures 2 and 3). The pulsing keeps the temperature from building up in the same way it would with a continuous wave and allows a gentle subclinical effect without the creation of a visibly identifiable burn.

Figure 2. Schematic of the temperature rise associated with a continuous wave laser application. The yellow bar represents the duration of the laser pulse and the red represents the rise and fall of the temperature of the treated tissues.

Figure 3. Schematic of micropulse laser. The yellow bars represent the effect of "slicing" up the continuous wave laser into small segments, with the wider bars representing larger duty cycles (the laser is on for a greater percentage of the duration of the exposure). You can see that the temperature in the tissue can be finely controlled to create separate elevations or gradually converging and increasing elevations depending on the duty cycle setting. (Figures 2 and 3 courtesy of G. Dorin, Ph.D., Iridex Corporation.)

Figure 2. Schematic of the temperature rise associated with a continuous wave laser application. The yellow bar represents the duration of the laser pulse and the red represents the rise and fall of the temperature of the treated tissues.

This approach is felt to create a very localized treatment effect—for instance, warming only the retinal pigment epithelium without affecting the underlying choroid or overlying retina.

How does it work? Well, since no one knows how any retinal laser really works, it is hard to say, but the philosophy would be that if a gnarly scar gets the job done, then perhaps gently heating cells without disrupting them might have some effect without necessarily causing permanent damage. There is a small literature suggesting that this approach can be effective, but at this point in time it is not clear how such techniques fit into the armamentarium—there are no large-scale controlled trials. There are other laser techniques being evaluated that are similar in philosophy—they all try to create a clinical effect without a destructive visible burn. The ultimate goal would be to use such techniques, perhaps in combination with pharmacologic treatments, in order to treat retinopathy without causing irreversible structural changes in the retina. It is worth keeping an eye on all these approaches—and if future studies demonstrate clear-cut efficacy, you can use this book for kindling or compost.

References and Suggested Reading

L'Esperance FA. Ophthalmic lasers, 3rd ed. St. Louis: Mosby, 1989.

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.

Luttrull JK, Musch DC, Mainster MA. Subthreshold diode micropulse photocoagulation for the treatment of clinically significant diabetic macular oedema. Br J Ophthalmol 2005;89:74-80.

Contact Lenses and the Wrangling Thereof

Becoming familiar with the contact lenses that are used to treat diabetic retinopathy is crucial. It is assumed that you have already mastered typical indirect non-contact lenses, such as the 90-diopter lens. But it turns out that contact lenses require a very different skill set, so they get their own chapter.

Contact lenses come in two main types: direct view lenses, such as the Goldmann three mirror, and inverted image lens system such as the Rodenstock. But first, a brief editorial...

This chapter will refer to several types of lenses. If you look at the manufacturers' catalogs, you will see that there are zillions of options. How can you try them to see whether they work for you? One option is to go to the manufacturers' exhibits at conventions. You will get a chance to try them all, but they never work as well on patients as they do on the little model eyes they use to demonstrate the lenses.

Another option is to dig around the back of all the drawers where your laser is kept. You will likely find a host of abandoned lenses, especially if you are in a large group practice or academic setting. Sometimes you will quickly realize why a given lens is in the graveyard, but sometimes you will find a real friend that works great for you. This also saves you a trip to the Academy meeting.

Above all, do not be fooled by the advertising that will have you thinking you will be able to treat patients effortlessly if you buy just the right lens. As you begin grappling with contact lenses, it is easy to think that your problems are due to the lens and that, somewhere over the rainbow, there is a perfect lens that will solve all your problems. You need to get over this phase quickly (otherwise, you will be spending a lot of money on lenses). It just takes practice— there is no secret magic lens.

Point-Counterpoint Box so the Lens Manufacturers Don't Get Too Ticked-off by the Previous Box Because We Need and Appreciate Their Constant Innovations

Although there is no magic lens that gets you over the hump of the learning curve, there is something to be said for having lenses that differ in subtle ways in order to address different nuances of treatment. Just like some guitarists prefer having a bunch of different instruments and others always use one favorite axe, you may find that you do better with lots of different lenses, or you may be happy with only one or two. Ultimately, this is something you will decide on your own once you have some skills with the basic lenses, so read on.

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Diabetes 2

Diabetes 2

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...

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