Ординатура / Офтальмология / Английские материалы / Hyperopia and Presbyopia_Tsubota, Boxer Wachler, Azar_2003

A B

C

Figure 1 (A) The human lens when not accommodating. (B) Accommodation according to Helmholtz’s theory. (C) Accommodation according to Schachar’s theory.

of the cornea. This technique, however, was primarily applicable to young presbyopes, as the average increase in the amplitude of accommodation was only about 1.50 D (16). Additionally, as the incisions healed, the effect regressed.

The first scleral expansion procedures using an encircling band were performed in 1992 (16). In these procedures, a plastic polymethylmethacrylate (PMMA) band (Fig. 2) was sutured to the sclera and covered with conjunctiva. The results were dramatic; however, the procedure was plagued with variable results, conjunctival erosion, and increased intraocular pressure. Various modifications were attempted to circumvent these problems. One such method involved passing portions of the bands through the sclera, forming scleral belt loops (17). This method did not include the use of scleral sutures in an effort to

Figure 4 Ultrasonic fusion of portions of a scleral expansion band.

Unfortunately, five of the six patients required removal of their scleral expansion bands 3 to 6 months later due to conjunctival erosion from the roughened areas where the PMMA bands were ultrasonically welded together. After removal of the scleral expansion bands, the accommodative amplitude of these five patients returned to preoperative values.

An additional three consecutive patients subsequently underwent the same procedure. In an effort to provide a better cosmetic result with more accommodation, the scleral belt loops were made much deeper. These three patients subsequently developed anterior

Table 2 Scleral Expansion Patient Selection

aImportant because of the investigational status of scleral expansion.

bThese patients should be informed of the possibility of ciliary muscle atrophy and thus the possibility of a smaller range of accommodation.

cThese patients should have surgical correction prior to scleral expansion, as they will use a significant amount of their accommodative amplitude for distance vision, leaving less for near vision. Additionally, without prior surgical correction of hyperopia, these patients are more likely to require bilateral procedures.

Source: Ref. 20.

Figure 5 The scleral expansion procedure. The conjunctiva is opened at the limbus from 2:30 to 10:30 o’clock and from 4:30 to 7:30 o’clock with vertical relaxing incisions at 12:00 and 6:00 o’clock. Scleral belt loops, 3.5 mm posterior to the posterior limbus, 4 mm long, 1.5 mm wide, and 300 to 400 m deep are made in each of the four oblique quadrants.

ischemic syndrome (AIS) and had their bands removed 24 to 96 h after surgery. Given previous reports of treatment of AIS with hyperbaric oxygen (18,19), we opted to treat these patients with hyperbaric oxygen. All patients responded well to hyperbaric oxygen therapy and none lost vision as a result of the procedure. This was the first known occurrence of AIS as a result of scleral expansion. Despite the posterior insertions of the rectus muscles, these deeper tunnels likely resulted in a significant reduction of blood flow through the anterior ciliary arteries that perforate the sclera at the insertions of the rectus muscles. In order to avoid compression of the anterior ciliary arteries and AIS, surgeons began placing the scleral belt loops along the 45-degree meridians at 1:30, 4:30, 7:30, and 10:30 o’clock.

Further modifications to the scleral expansion band followed. Unfortunately, conjunctival erosion continued to be a problem. In 1998, however, a new prototype was developed consisting of four individual PMMA segments that were not connected to each other, resulting in decreased rates of conjunctival erosion, a simplified procedure, and a significant decrease in instrumentation cost (120). To decrease the risk of AIS, these segments were also placed in scleral belt loops along the 45-degree meridians, away from the ciliary artery insertions (Fig. 5).

Not everyone, however, is a candidate for scleral expansion. See Table 2 for patient selection.

C. CURRENT METHOD OF SCLERAL EXPANSION

1. Preop Medications

If the patient has no contraindications, it has been recommended that oral nonsteroidal anti-inflammatory drugs (NSAIDs) be started 1 to 2 days preop. Nonsteroidals decrease surgical pain and swelling and produce a smoother postoperative course. Additionally, there is some thought that NSAIDs may help to preserve anterior segment circulation (70).

Figure 6 Marking the limbus with the quadrant marker.

Mark the 12 o’clock position at the slit lamp. This is an important reference mark to be used later for proper segment placement away from the area of ciliary arteries. If this reference mark is not made, cyclotorsion of the eye can occur when the patient lies down for the procedure. This will increase the risk of anterior ischemic syndrome from malpositioned segments. After the patient is taken to the operating room, the 12 o’clock meridian is used to align the quadrant marker in order to mark the location of the scleral expansion segments (Fig. 6.).

D. ANESTHESIA

A small amount of subconjunctival anesthesia is injected at the 12:00 and 6:00 o’clock meridians to elevate the conjunctiva and produce a surgical plane for dissection. Retrobulbar and peribulbar anesthesia is generally avoided because the pupil dilates and the eye may become soft, making it more difficult to construct the scleral belt loops. Additionally, a dilated pupil precludes evaluation of iris sphincter function, which is necessary to assess anterior segment circulation.

E. CONJUNCTIVAL DISSECTION

A 4 to 5-mm vertical incision is placed perpendicular to the limbus at the 12 and 6 o’clock meridians. These incisions are extended circumferentially at the limbus approximately 1 mm past the oblique quadrant marks. The conjunctiva from 7:30 to 10:30 o’clock and from 2:30 to 4:30 o’clock is left intact to avoid postoperative redness in the palpebral opening. The flap is dissected approximately 5 mm posterior to the limbus, leaving no Tenon’s capsule in the area where the scleral expansion segments will be placed. As little cautery as possible should be used so as to preserve the structural integrity of the sclera.

Figure 13 The thickness of the scleral belt loops and the exit wound are checked with the 1.4- mm-wide spatula.

seen through the sclera, then the loop is too shallow and the effect of the surgery will be greatly reduced. In making the scleral belt loop, care should be taken not to retract and advance the blade unnecessarily to avoid making blind pockets that will increase the difficulty of passing the scleral expansion segment.

On nearing the exit incision with the diamond blade, the sclera is depressed with the scleral fixator to help open the exit incision. It is usually necessary to aim the lamella blade upward just before exiting to prevent a blind pocket under the exit incision. The entire lamella diamond blade is 5 mm long. The front curve of the blade is 1 mm long. Therefore, by seeing the complete front curve of the blade, the surgeon is assured that the scleral belt loop is no longer than 4 mm.

In removing the lamella diamond blade, the surgeon must maintain fixation with the scleral fixator and remove the lamella blade slowly and in a controlled manner. In doing so, the surgeon avoids cutting the edges of the entrance incision, avoids perforating the belt loop, and ensures that the blade is not passed into the suprachoroidal space. If there is any doubt that the lamella blade is completely passed through the exit incision, test the incision using a 1.4-mm-wide spatula (Fig. 13). It should be possible to readily pass the spatula through the incision in the same direction that the scleral expansion segment will be passed.

H. PLACE THE SCLERAL EXPANSION SEGMENTS

The four scleral expansion segments (Fig. 14A and B) come packaged in much the same way as an intraocular lens (IOL). Prior to grasping the segments, place one or two drops of sterile saline into the well holding the segments. This prevents loss of the segments due to static electricity. Either a specifically designed scleral expansion segment holder or the injector can be used to pass the segment through the scleral belt loop (Fig. 15). Load the segment into the injector or segment holder curved side up. Without moving the scleral fixator, the segment is passed into the scleral belt loop. In difficult cases it is