Scleral ECCE wound

The architecture of the wound is similar between scleral and corneal ECCE wounds but, for a scleral wound, the conjunctiva must be reflected first and sutured back in place at the end. If a very peripheral corneal wound is made then consideration should be given to moving the conjunctiva as well because if this is not done the closing sutures which start in the cornea will exit through the sclera and conjunctiva and will ‘cheese-wire’ or cut through the conjunctiva leading to inflammation, sterile conjunctival infiltrates, and loosening of the sutures.

The wound is sloped backwards meaning that the blade used for the incision is pointing towards the surgeon. This makes the wound self-sealing and stable. If the wound is forward sloping it will leak and make the operation difficult and the postoperative period more risky.

The scleral wound is made around 120°, initially backward sloping and then, when the deeper tissues are reached, a forward entry into the eye is made (Fig. 11.1). More bleeding is likely because of perforating scleral vessels and diathermy is a prerequisite. Careful wound construction and suturing can be rewarded by very little surgically induced astigmatism because of the distance from the optical centre of the cornea and the ability to leave the sutures at the desired tension.

Fig. 11.1 Construction of a corneal wound. The wound is either perpendicular or slightly backward-sloping (A) with respect to the corneal surface to ensure that it is self-sealing. The job of the sutures is then not to keep the wound closed, but simply to stop it opening. (B) The wound in cross-section, backward sloping with respect to the surface of the cornea.

Redrawn from Benjamin L, Surgical Techniques in Ophthalmology: Cataract Surgery, Elsevier, 2007.

Excessive cautery may shrink the edges of the wound and make wound apposition more difficult when closure is attempted.

Corneal ECCE wound

This should be made approximately 1 mm into clear cornea and sloped gently backwards. This ensures that the sutures when placed to close the wound will enter and exit corneal tissue and avoid the need for reflecting the conjunctiva (see Fig. 11.1).

The wound is made at least 90% depth and then a final, forward entry into the anterior chamber is made. A diamond bladed knife is best for this but a sharp steel blade is adequate, more readily available and much cheaper. Re-used steel blades blunt very quickly and should not be relied on as soon as their lack of sharpness is perceived.

The relative advantages and disadvantages of scleral and corneal ECCE wounds are summed up in Table 11.1.

Table 11.1 Comparison of corneal and scleral section

Scleral tunnel phaco wound

See Figure 11.2.

Fig. 11.2 (A, B, C) A surgeon’s view and side view of the initial one-third thickness scleral groove being made, the conjunctival flap having been moved from the limbus (D, E, F). The second stage of the procedure is a bevel up crescent blade used to create a scleral pocket. The pocket is roughly square and advanced into clear cornea, kept parallel to the surface of the eye. (G, H, I) Once the slit knife is entered into the pocket, initially with the same trajectory as the pocket was constructed, the heel of the blade is lifted and the blade inserted into the anterior chamber, parallel to the iris. This creates a two-step, three-plane wound.

From Benjamin L, Surgical Techniques in Ophthalmology: Cataract Surgery, Elsevier, 2007.

The conjunctiva is reflected and a frown or straight incision made approximately 3 mm long and around one-third scleral thickness. A bevel-up crescent blade is then used to dissect forwards towards the limbus until the edge of the blade is just visible in the corneal stroma. This gives a square tunnel of approximately 3 mm sides. A predefined width keratome (to match the size of the phaco probe and sleeve) is then used to enter the AC in a plane parallel to the iris. It may not be necessary to suture the wound closed at the end of the procedure, but if there is any concern about its stability this should be undertaken with an 8 or 9-0 absorbable suture. The conjunctiva should also have a suture placed to close the superficial wound.

Corneal tunnel phaco wound

See Figure 11.3.

Fig. 11.3 (A–G) Corneal wound construction. These steps are similar to those for a sclera tunnel but are often modified to miss out the formal formation of a pocket. A groove, as seen in (A), is still useful as a guide for centering the slit knife and also to provide the first step of the wound. Note the difference in angle of the blade between (D) and (F).

From Benjamin L, Surgical Techniques in Ophthalmology: Cataract Surgery, Elsevier, 2007.

This wound may be constructed in the same way as the scleral tunnel albeit with a shorter length for the second stage. Some surgeons prefer to miss out the initial 3 mm groove (it has been shown by anterior segment UBM to cause slight gaping of the epithelium) and also the formal dissection forward of the corneal stroma. Instead they use the keratome to make an initial entry into the stroma, superficially and parallel to the surface of the cornea, and then, using the engaged tip of the blade, elevate the heel of the blade so its point is pointing into the AC, pushing the tip through full thickness cornea to enter it into the AC before levelling it out again to fully enter the AC parallel to the iris without damaging the lens capsule. The length of this tunnel can be altered by changing the distance traveled through the stroma before changing direction into the AC. A length of 1–2 mm is ideal and certainly adequate.

Postoperatively, the corneal stroma at the wound edges should be hydrated as this ensures greater safety from postoperative ingress of fluids into the eye and may well help to reduce the incidence of endophthalmitis2.

Astigmatic considerations

For patients with less than 1.5 diopters of astigmatism and using a technique which is known to induce little astigmatism, the wound can be placed wherever it is most comfortable for the surgeon. It must be remembered that, if training is taking place, the training surgeon must be in a position to take over from the trainee if necessary, so the wound placement should be such that this is possible. For example, if a left handed trainee places the wound nasally in a right eye, a right handed trainer would find this difficult to cope with.

If more than 2 diopters of astigmatism exist then consideration should be given to placement of the wound to reduce the steep meridian astigmatism (i.e. at the head of the steep meridian).

If more than 2 diopters of difference exis between the K readings then additional maneuvers can be undertaken to reduce astigmatism. Examples of these are limbal relaxing incisions (LRIs), opposite clear corneal incisions (OCCI), arcuate keratotomies (freehand or using preset blades), which may be single or paired, or ‘T’ cuts.

Each method has a range of published studies using different nomograms which relate with or against the rule astigmatism to patient’s age and intended correction. Thus a typical formula might be to place paired arcuate cuts 8 mm apart from each other, of 3 clock hours length each and 600 microns in depth. Each nomogram is approximate and relies on experience and consistency to obtain reasonable results.

Another approach is to consider the use of toric intraocular lenses which allow routine wound placement and allow astigmatism correction with no alteration to the corneal surface. This is becoming more popular as commercial companies are now producing a greater range of lenses with which to perform these corrections.

Access considerations

A deep set eye in a patient with prominent brows will be much more easily approached from the temporal aspect than the superior one. Similarly, a pre-existing trabeculectomy bleb will restrict access in some eyes and a temporal approach will again be easier. The horizontal diameter of the cornea being longer than the vertical one means a temporal wound will induce less astigmatism for a given wound length than a superior one. However routine placement of the wound in this position will mean that some patients will have their astigmatism increased by virtue of the fact that they have with the rule astigmatism. Routine analysis of the K readings should therefore be undertaken in all patients so as to avoid astigmatic surprises postoperatively.

Side port construction

One or two side ports are used for a second instrument or for separate irrigation/aspiration access. These wounds should be made as small as possible whilst still allowing atraumatic insertion of the instruments. If one of the ports needs to be enlarged at some point (e.g. to allow the use of a Simcoe cannula for I/A), then this should be done only after the phacoemulsification is complete so as to allow the anterior chamber to stay stable during the phaco process. If the side ports are overenlarged the AC will be unstable due to fluid loss.