Endolaser

Abstract

The result of the treatment is a scar that involves the outer retina. Endolaser, with the proper parameters, is a very effective weapon and is often employed and for various purposes: destroying retinal areas with nonperfusion, inducing chorioretinal adhesion around an existing retinal break or preventing a retinal break from leading to RD, walling-off a pathology such as retinoschisis to prevent it from spreading, etc. The use of endolaser in the retinal periphery is a significant challenge to the beginner surgeon and requires many tricks and technical adjustments so that he can overcome his initial frustration.

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Laser, as photocoagulation in general, uses light to cause tissue coagulation as the energy from the light source is absorbed by the tissue and converted into thermal energy.¹ Laser’s significant therapeutic benefit is thus delivered via a force that is destructive in nature.

Laser to the retina is typically applied at the slit lamp or via the IBO. Unlike endolaser, with these techniques the laser is delivered from outside the eye. Both involve at least some inconvenience to the patient,² and even if retrobulbar anesthesia is used, treatment close to the fovea poses some risk of misdelivery.

All other parameters (see Table 30.1) being equal, three factors determine the effectiveness of the laser therapy: the depth of penetration of the laser beam³ and the type and amount of tissue pigment⁴ that absorbs the laser energy. Table 30.2 provides a list of selected conditions in which (endo)laser⁵ therapy is applied.

Table 30.1 The parameters influencing the efficacy of the endolaser

Table 30.2 Selected indications for endolaser therapy

Endolasers of different types⁶ are available; the use of Argon green (514 nm) is described here.

1 The Consequences of Laser Treatment

• The retina becomes edematous after laser treatment. The surgeon notices that within a few seconds, the spot, which was white with sharp borders upon delivery, turns fuzzy-bordered, and its color turns a bit grayish.

• With time,⁷ the spot turns into a scar. The RPE, the photoreceptors, and the retinal layers external to the inner nuclear layer are involved in the scar; there is some hyperplasia and hypertrophy of the remaining RPE. Glial cells also contribute to the development of the scar.

  • The visual consequence of the scar is a miniature, focal scotoma: the overlying nerve fibers are spared (see Fig. 51.4).

  • If too high laser power is used, all retinal layers, including the nerve fibers, are scarred over.⁸

  • The size of the scar increases by ~50% with time.

Q&A

Q:

What may be the undesirable consequences of an “overpowering” (endo)laser spot?

A:

Pain, even if the rest of the operation was painless; corresponding defect in the visual field; significant retinal bleeding; retinal break formation; break in Bruch’s membrane with development of a neovascular scar; if a spot is close to the fovea, RPE migration into it with loss of the central vision; and the vitreous “burned” into the scar, making PVD creation impossible.

• After treatment, the oxygen consumption of the retina is reduced.

  • Oxygen is able to diffuse through the laser scars without being consumed by the photoreceptors, relieving the inner retinal hypoxia and raising its oxygen tension.

  • The retinal arteries constrict and the blood flow decreases. The hypoxia relief reduces VEGF production, and the neovascularization process stops or regresses.

2 The Setup

The initial step is to ensure that the laser filter is properly situated on the microscope. It should be mounted so that it provides protection for the surgeon, his assistant, the nurse, and the video camera. The first three are a matter of safety⁹, the fourth of convenience. It is advisable for all in the OR to wear safety goggles when the endolaser is in use.

The laser pedal should be in the middle (see Fig. 16.3a) and operated by the nondominant foot.

3 The Technique of Endolaser Treatment

Unlike cryopexy, laser is ineffective if applied over detached retina.¹⁰ This is the reason why, for instance, in RD surgery laser is delivered after drainage of the subretinal fluid and under air.

Pearl

As a general principle, the parameters should be adjusted so that the effect is a discreet but visible whitening of the retina with no apparent major tissue disruption (strong whitening, bubble formation, significant bleeding, audible “pop”).

3.1 General Considerations

To deliver a spot that causes mild retinal whitening, all three main parameters must be properly set.¹¹

• My default parameters are the following:

  • Duration, 100 ms; spot size, 100 μ; energy, 150 mW.

  • Since the effect also depends on the pigmentation of the fundus,¹² major changes in the settings may become necessary. It is best to test the parameters at a peripheral location (see below).

• An additional parameter to set is the “repeat” mode (see below).

• Ideally the laser probe is curved so that the surgeon can always keep it perpendicular to the surface and be able to reach any retinal area without difficulty or risk in the phakic eye.

  • The straight probe has significant limitations regarding reach and safety.¹³

  • The curved probe (may be retractable if made of memory material) can be held truly perpendicular to the retina at all locations – but the surgeon must remember to pull the laser probe into the shaft before exiting the cannula with it (see Sect. 21.7).

  • In a phakic eye it is possible with the curved probe to avoid damaging the lens, but extra caution is still needed: the surgeon tends to focus on delivering the laser spots, not on the actual position of the laser probe’s shaft.

• The spots should not be confluent; as a general rule, the distance between spots should be roughly the same as the spot diameter.

  • When panretinal treatment is employed, this rule is difficult to keep (see below).

• The working distance¹⁴ is typically ~1–2 mm – with some caveats.

  • When lasering under air (see Sect. 31.2), it may be difficult to clearly see the tip’s distance from the retina, especially in the periphery. The laser probe must be advanced close to the retina,¹⁵ and the surgeon should carefully observe the distance between the shaft’s tip and the shadow it casts.

  • Different areas in the fundus have different degrees of pigmentation. If the laser power proves too strong (weak) at the “test site,” it is more efficient to increase (decrease) the working distance than continually adjusting the power on the console.

Pearl

When working in “repeat” mode (see below), too short a working distance is dangerous: it is easy to bump into the retina as the probe is moved along.

• The initial “test” spot should always be delivered well outside the macula. If no effect on the retina is seen, examine the aiming beam (this may tell you whether the cable is broken) before you increase the power/duration or shorten the working distance.

• PFCL has a cooling effect and this makes recognition of the spots more difficult – overtreatment is a risk.

• Avoid lasering a hemorrhage¹⁶ since the blood may absorb it and cause damage to the more superficial retinal layers.

Pearl

It is somewhat controversial whether a posterior retinal break or retinotomy (i.e., in an area where the vitreous has been verifiably removed) requires laser treatment. In principle, the answer is no, since no traction is left behind; the laser spots also increase the size of the scotoma. In practice, laser may make sense because of any possible future traction. An individual decision is needed (I very rarely do laser for posterior retinal breaks; see also Sect. 8.1).

• Edema, whether caused by RD¹⁷ or other conditions, reduces the efficacy of the treatment.

3.2 Panretinal Treatment

The technique presented here about the order of spot placement reflects my personal approach. Every surgeon must develop his own philosophy – what matters is that some kind of order be kept.

• I initially apply 2–3 rows in a circle around the macula so as to reduce the risk of inadvertently venturing too close to the fovea during the delivery of many hundreds of laser spots.¹⁸

• I follow with the full treatment on the opposite side of the retina, then switch hands to complete the laser application on the other half of the fundus.

• Usually I do the treatment centrally first and in the periphery second, due to the ease of maintaining visibility, especially in the pseudophakic eye (see below). It is advisable to use the dominant hand to complete the laser application at the posterior pole.

• Switching hands at some point is unavoidable in order to complete the treatment.

  • When to switch hands has no strict rule: it need not be exactly at the 6 and 12 o’clock meridian. When the spots are becoming oval, a switch is in order.

Q&A

Q:

May the surgeon complete the panretinal laser coagulation during the same operation, or should it be finished during a 2nd session at the slit lamp or via the IBO?

A:

Even 1,500–2,000 spots, delivered during a single session (see Fig. 30.1), have not been associated with any detrimental effect – in fact the outcome may be better than with multiple sessions. The reason why multiple sessions are used at the slit lamp has more to do with patient comfort and convenience, which are not an issue with endolaser (Using micropulse laser at the slit lamp, it is now possible to complete the treatment in a single session.)

Fig. 30.1

Panretinal endolaser. The treatment of the posterior pole has just been completed; the spots are white and only slightly edematous. The curved (non-retractable) endoprobe is still visible inferiorly

• I always use the “repeat” mode of the laser equipment; no surgeon should be forced to step on the laser pedal 1,000 times. This is not only inconvenient but also risky: eventually you will have to readjust your posture and may accidentally deliver laser to an unintended location.

Pearl

The more experienced the surgeon, the shorter the repeat time can be.

• The edge of the IOL causes parallaxis (see Sect. 25.2.4.3). The surgeon, if the pupil is wide enough, will have to alternatively view the retinal periphery outside or through the optic.

  • If this is the case, it is best to finish a large area’s laser treatment viewed either outside or through the optic and then move on to the other area. Switching the view back and forth in quick successions is tiresome.

• When lasering close to the macula, extra steps are necessary to avoid “hitting the bull’s eye.”¹⁹

  • Use the single, not the repeat, mode (one spot per one pedal pressing).

  • Make sure the spot is not too strong (see above).

  • Avoid lasering in the foveal avascular zone (see Sect. 26.1.3).

• If the laser is employed for macular edema, inject bevacizumab or TA a few days earlier so that the macula is rather dry at the time of surgery, and then try “laser maculopexy” (see Fig. 30.2).

Fig. 30.2

Laser maculopexy. The macula has been dried with a prior intravitreal bevacizumab injection (see the text for details). A circular laser treatment is delivered close to the avascular zone to act as “nails” to reduce the risk of re-swelling of the retina

Pearl

All ophthalmologists must keep in mind that with time the optic disc will turn pale after panretinal laser treatment. This is a normal phenomenon and must not be appreciated as a disease-related atrophy.

3.3 Endolaser Cerclage and Its Complications

A variant to panretinal treatment, this laser is aimed at preventing RD or redetachment.²⁰

• Deliver a more compact treatment²¹ than for panretinal lasering (see Fig. 30.3).

  Fig. 30.3

  

  Endolaser cerclage. (a) Endolaser cerclage is being performed. The posterior border of the area to be treated is posterior to the equator. (b) The healed spots form a confluent area of scars to counteract the effects of any remaining or new traction (or retinal break) in the anterior retina

  • In an emmetropic eye, 900–1,200 spots are needed.

• The area to treat is from the ora serrata to slightly central to the equator (see Fig. 30.3).²²

• At the 3 and 9 o’clock positions, reduce the power/number of laser spots to avoid damaging the long ciliary nerves. A dilated pupil is one of the potential complications of endolaser cerclage.²³

  • The other complication, just as with panretinal treatment, is EMP, occurring in 1–2% of the eyes. Prophylactic ILM peeling should be considered.

Endolaser cerclage is best done using the wide-field front lens of the BIOM under air²⁴; this allows visualizing the retina up to the ora serrata if the pupil is wide enough. An alternative option is scleral indentation.

Pearl

If the RD risk is similar in the fellow eye, prophylactic endolaser cerclage must be discussed with the patient (see Sect. 42.1). If done properly, such an intervention is almost a guaranty against future RD (see Sect. 54.2.4.1).

3.4 Endolaser as a Walling-Off (Barricading) Tool

• In eyes with peripheral retinoschisis, the purpose of the laser treatment is twofold:

  • By creating a barrier of adhesion, it prevents progression of the condition toward the macula.

  • By marking the border of the pathology, it allows the ophthalmologist to accurately monitor whether progression has occurred.²⁵

• In eyes with PVR or PDR and partial RD whose progression is prevented by silicone oil, the laser barricade acts as an additional weapon in maintaining retinal attachment.

The laser spots should be tightly placed (see Fig. 30.4) or be “painted” by continuous application and extended all the way to the ora serrata on both ends to prevent the intraretinal fluid to “come around the laser wall.” The treatment must be especially firm inferiorly, where, due to gravity, the risk is higher than in the superior part. 2–3 rows are needed to ensure maximum effect.

Fig. 30.4

Walling-off laser. The retinoschisis (S) is surrounded by two contiguous rows of laser applications (represented by white circles) to prevent progression of the condition into the attached retina (R). See the text for more details

3.5 Endolaser as a Welding Tool

• The retinal break is the most common indication and has the same goal as in the case of cryopexy (see Fig. 29.1b). The laser spots must surround the break in a contiguous fashion, by 2–3 rows.

• A retinotomy that is posterior so that all vitreous can safely be assumed to have been removed does not require laser treatment – but the surgeon may feel he will sleep better if he does it. If the retinotomy is in an area where it is not certain that the vitreous removal was complete (see Fig. 63.9), it is advisable to surround the lesion with laser.

• Following retinectomy,²⁶ a laser treatment similar to that shown on Fig. 30.4 is recommended to prevent elevation of the remaining retinal edge.

4 Peripheral Laser and the Beginner VR Surgeon

Performing panretinal laser in the periphery, and especially laser cerclage, is perhaps the most frustrating part of VR surgery for the beginner. The procedure appears rather easy when viewed through the assistant’s microscope or on a videotape but can be cruelly difficult when performed, for numerous reasons.

• Visibility is poor, especially if the laser is performed under air and in the pseudophakic eye, due to parallaxis, and if either of the capsules is hazy (see above). It is difficult to view the retina, the tip of the laser probe (i.e., the proper working distance; see above), and the delivered laser spot unless the power is too strong.

  • Condensation of the back surface of the IOL in the air-filled eye adds to the difficulty (see Fig. 25.2).

• Occasionally, even if visibility is acceptable, no visible laser spot appears after the application. One of the many possible causes²⁷ is that during the previous spot, the tip touched the retina and the surface is covered with tissue.

  • If the laser is performed under fluid, any small air bubble that is inside the vitreous cavity will adhere to the tip of the probe and prevent laser delivery.

• The most distal portion of the shaft should be held perpendicular to the retina (the plane of the tip itself is parallel to it). If a straight probe is used, the surgeon has no control over this, and the shape of the laser spots will become oval. If a curved probe is used, the procedure’s technical complexity grows because the surgeon must adjust the position of the probe according to how the geometry of the treated area (in effect the angle between retina and the probe itself) changes.

  • If a retractable probe is used (see Fig. 30.2), one possibility is to increase or decrease the length of the shaft. This allows the surgeon to maintain the correct angle between the shaft and the retina, but the adjustment is rather cumbersome and somewhat dangerous.²⁸

  • A better option with the retractable probe (and with a probe whose curvature is fixed, see Fig. 30.1) is to twist the shaft around its main axis. In most areas, it is easy to have visual feedback of the position (angle) of the bend, but in the horizontal meridian, the surgeon sees the shaft as a straight line; it is impossible to determine whether concavity of the bend on the probe points upward or downward.

  • The further the probe is away from the horizontal meridian, the more sideways it will be held,²⁹ increasing the visibility of its curvature.

• The light pipe’s position must also be monitored to avoid bumping it into the retina or the lens.

  • Even if the retina is not injured mechanically, phototoxicity remains a risk if the light pipe is held too close to the retina (see Sect. 22.1).

• In addition to the constant adjustment of actions of the two hands described above, the surgeon’s two feet must also have closely coordinated movements (with each other and with the hands): the nondominant foot operates the laser pedal, the dominant foot the X/Y joystick (see Fig. 30.5).

  Fig. 30.5

  

  Schematic representation of the adjustment of the image during endolaser cerclage. If an object (black dot), which is in another room and partially hidden behind the wall (W), is to be viewed through a doorway, the observer (O) simply moves so that the view is unobstructed (thin arrow). If the retinal periphery is to be viewed through the BIOM, sometimes the opposite is needed: moving as if further behind the wall (thick arrow)

• The process is lengthy; the surgeon’s eyes become dry and his lower back starts to hurt (see Chap. 16).

• The patient’s nose may be in the way.

Pearl

To avoid the frustration, do not start performing laser cerclage early in your VR career, and even then do it only gradually (smaller, more central areas but away from the macula first). Do not be discouraged by the early difficulties; all surgeons had to go through the same process.

5 Endocyclophotocoagulation

If the IOP is high and cannot be controlled medically, one of the many options is cyclodestruction. Proper scleral indentation by the surgeon (see Sect. 28.4) allows visualization of the ciliary processes, which can be individually shrunk by applying high-power laser treatment (see Fig. 30.6). The effect is both visible and occasionally audible (see Chap. 25).

Fig. 30.6

Endocyclophotocoagulation. Scleral indentation brings the ciliary processes into view; laser is applied to destroy the selected processes. The infusion cannula is also visible inferiorly

Even though the success rate of the intervention is usually rather limited, do not treat more than 180° in the initial session: the effect on the individual process is irreversible.

6 Laser Cerclage at the Slit Lamp

It is possible, even if more difficult, to perform proper treatment at the slit lamp. Instead of the three-mirror contact lens, use a contact lens with a very large field³⁰ and try to achieve a similarly wide zone of treatment as described above (Sect. 30.3.3).