Intraoperative Slit Lamp Illumination
In combination with the microscope, this provides clear ILM and interface visualization and other benefits.
DIDIER DUCOURNAU, MD

Although the great majority of ophthalmologists worldwide systematically use a slit lamp for the clinical diagnosis of ocular diseases, by a curious paradox, they neglect their emblematic instrument as soon as they enter the operating room. I have been using, for the past 20 years, a slit lamp attached to the operating microscope and positioned at 5° from the axis as my unique illumination system for more than 13000 internal limiting membrane (ILM) removals and 10000 vitreoretinal interface examinations during retinal detachment surgery.

This is advantageous because the slit provides an optical cut of the vitreoretinal interface, and the tilt at 5° allows the visualization of the ILM reflect. The slit lamp also offers advantages in external procedures and in vitrectomies for retinal detachment treatment. Here, I explain all of these advantages.

	Figure 1. With a slit lamp light illuminating the macula at an angle of 5°, right, the great majority of reflected light reaches the surgeon's eye.
	Figure 2. With slit illumination, the surgeon can analyze vitreous traction and then adapt the surgical strategy.
	Figure 3. During scleral depression, remaining adherent vitreous fibers supported by the indentation will be highlighted by slit illumination.
	Figure 4. Motorized slit lamp on a circular rail.

FOR MACULAR SURGERY

For ILM visualization and manipulation during macular surgery, the addition of the surgical slit lamp offers many advantages:

Better visibility of diffracted light and then of the gliosed ILM reflect, thus avoiding the use of coloring agents. Indeed, the endoscopic light source, or a light fixed to the sclera at 3 mm from the limbus, illuminates the macula at an angle of 25°; the great majority of reflected light does not then leave the ocular globe. On the contrary, with a slit lamp light illuminating the macula at an angle of 5°, the great majority of reflected light will reach the surgeon's eye (Figure 1).

Lower cost. Using a slit lamp makes it unnecessary to buy disposable intraocular fibers and coloring agents. In my clinic, this allows us to save, every year, the total price of a new surgical microscope plus a new vitrectomy machine.

Lower trauma for many reasons. A third sclerotomy is no longer necessary, which means less scleral trauma, less risk of vitreoretinal incarceration, and less risk of touching the crystalline lens or inducing vitreous traction due to manipulations of the intraocular fiber. The risks of injecting coloring agents are eliminated. There is less risk of phototoxicity because a slit light at 5°, focused on the macula, provides a fixed illumination of 7000 lumens, the same as with an intraocular fiber placed at 17 mm from the macula. If the fiber is 4 mm away from the macula, it will provide a 135 000 lumens illumination.

More precision. Under the slit light illumination, the surgeon's left hand is free to manipulate the eye and to stabilize the forceps, thus increasing precision and safety. Which anterior segment surgeon would monopolize his left hand to hold an illuminating fiber? So, why should posterior segment surgeons do so?

Faster procedure. It is not necessary to open and close a third sclerotomy. Injecting and removing coloring agents, or removing additional vitreous to make room for the agents, are not necessary.

In addition, trembling movements during the dissection are not an issue because the surgeon's left hand is stabilizing the forceps.

At the end of the day, this approach saves time and energy. I'm performing 14 macular surgeries in the first 4 hours of each operating day, and this saves me time and energy to carry out more difficult cases in the afternoon.

FOR RETINAL DETACHMENT SURGERY

As you know, in 80% of cases, retinal detachments are the result of vitreous traction. The optical cut provided by the slit lamp allows visualization of the vitreous and vitreoretinal interface. The surgeon can therefore analyze a static vitreous traction at the vitreous base level, or a dynamic traction still active at the origin of the retinal tear, and then adapt his or her surgical strategy (Figure 2).

Without this optical cut, it can not be determined during the procedure whether relaxation of the traction is sufficient or if cutting is needed. This is why it is confusing when surgeons who use the slit lamp and surgeons who use indirect ophthalmoscopy talk about surgical strategy.

In addition to this advantage, using the slit lamp is beneficial in external procedures and vitrectomy for retinal detachment. For ab externo approaches:

► The adjustable magnification of the microscope enables the localization and treatment of peripheral retinal lesions as small as 50 microns, which would not have been seen without magnification. A systematic circular buckling for security reasons is therefore not compulsory.

► The surgeon remains seated during the procedure and does not have to stand up and turn around the table for every retinopexy or control. This increases efficiency, precision and comfort.

For vitrectomy:

► The optical cut provided by the slit allows the visualization of the posterior capsule during removal of the anterior hyaloid. The surgeon works in close proximity to the capsule but avoids direct contact.

► With the free hand, the surgeon can perform the peripheral scleral depression alone, thus increasing both precision and speed. The two-handed work is performed instinctively, with continuous visualization from the optic disc to the ciliary body. For me, this is the best advantage of this technique. It is the only way I have found that allows me to perform a complete vitrectomy without any exit of the handpiece, thus decreasing the risk of vitreoretinal incarceration. Unlike with illumination systems fixed to the sclera, there is no risk of the manual indentation causing contact with the crystalline lens.

► During scleral depression, the remaining adherent vitreous fibers that are supported by the indentation will be highlighted by the slit illumination because of its tangential position (Figure 3).

► In case of a very difficult dissection, a third sclerotomy can be performed in order to allow an instinctive bimanual dissection, without any need for a special illuminating instrument.

FUTURE TOOLS WILL ENHANCE THE BENEFITS

It is possible to combine a slit lamp and operating microscope using equipment from several companies, including Zeiss, Moeller-Wedel, Oculus and Leica, but the current setups, built on a circular rail (Figure 4), are somewhat cumbersome and prevent use of some wide angle viewing systems. To overcome this inconvenience, Topcon has proposed a new system that incorporates the slit lamp within the operating microscope. The introduction of such a setup will likely facilitate more universal use of slit illumination in the operating room.

Address correspondence to: Didier Ducournau MD, Clinique Sourdille, 3 Place Anatole France, 44000 Nantes, France, Telephone: + 33 251 833 260, Fax: + 33 251 833 261, E-mail: ddd@club-internet.fr.

From Clinique Sourdille, Nantes, France. Dr. Ducournau has no financial interest in the instruments discussed in this article.