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Inside Eyetube.net | Oct 2012

A Tale of Two Myopes

With the same degree of myopia but different ages, patients may benefit from alternative surgical approaches.

A 60-year-old patient with -8.50 D of myopia and signs of early cataract and a 35-year-old patient with -8.50 D of myopia and healthy eyes represent very different scenarios for surgical decision-making. On the one hand, the 60-year-old with early cataract will already have some visual impairment that is not correctable with glasses or contact lenses. The 35-year-old is likely someone who desires spectacle independence as a lifestyle choice. Thus, different procedures will be appropriate to improve the vision of each patient.

Patient No. 1

preoperative considerations

The 60-year-old, -8.50 D myopic patient has minimal accommodation left, and his cataract will need to be removed and replaced by an IOL. The power of this lens must be accurately determined, preferably by using an optical biometry device such as the IOLMaster (Carl Zeiss Meditec) or Lenstar (Haag-Streit). At this level of myopia, there is probably not a posterior staphyloma present, but, if on fundoscopy there appears to be a degree of myopic degeneration, an ultrasound B-scan is worth considering. If a B-scan is performed, it will be possible to assess whether a posterior vitreous detachment has occurred. Some consider this protective of possible future risk of retinal detachment. Certainly, as part of the informed consent, the patient must be warned of the increased risk for retinal detachment, particularly in men. The patient will have had a full retinal examination to determine if any predisposing retinal pathology is present; however, current thinking suggests that lattice degeneration should not be treated prophylactically unless symptoms have been associated with it.

The SRK-T, Holladay 2, and Haigis formulas are recommended for lens calculation. The choice of lens type will depend on a patient’s requirements for postoperative vision. Many myopes will take the opportunity to become more spectacle independent, and thus, some sort of bifocal such as the ReStor (Alcon Laboratories, Inc.) or Lentis MPlus (Oculentis GmbH; distributed by Topcon), or one of the newer trifocals such as the FineVision (PhysIOL) or AT LISA tri (Carl Zeiss Meditec) may be considered. Appropriate preoperative counseling will avoid postoperative issues in terms of unmet expectations.

surgical procedure

Wounds. The sclera in a myopic eye is generally less rigid, and therefore good wound construction is important, as is using the smallest incision possible, such as with coaxial microincision surgery. I prefer to use a Windsor knife (Core Surgical) to create a three-plane incision that will seal at the end of the procedure.

Capsulorrhexis. Because the pupil in myopic eyes often dilates widely, it is important not to follow close to the edge of the pupil when making the capsulorrhexis, or it will be too large. This is particularly important in large myopic eyes, in which there is a risk of greater dysphotopsia if the lens edge is not covered by the rhexis edge. Using capsulorrhexis forceps with a measure on the blades may be useful.

Avoiding an over-deep anterior chamber. One of the most important factors in successful cataract surgery in myopic eyes is avoiding an over-deep anterior chamber, for two reasons. First, surgery is more difficult when the phaco needle and the second instrument are held at steep angles in the eye. This may lead to a greater risk of posterior capsular rupture, as the anterior chamber is often unstable as well. Second, if the surgery is being carried out under topical anesthesia, the patient will feel pain if the chamber deepens suddenly, as it does when irrigation is introduced into the eye. It is possible to avoid this by using a few simple maneuvers each time the eye is entered with irrigation (ie, at the beginning of phaco, at the start of irrigation and aspiration) and when the ophthalmic viscosurgical device (OVD) is removed at the end of the case. The steps are as follows:

  • Ask the nurse to lower the irrigation bottle to 45 cm;
  • Enter the eye with the phaco probe with no irrigation;
  • Pass the second instrument through the sideport across the eye and lift the iris;
  • Press the footpedal of the phaco machine to position 2; this will allow the eye to fill slowly, and fluid and OVD will be drawn from the eye (Figure 1);
  • Ask the nurse to raise the irrigation bottle to the normal operating height.

If one follows this procedure, the chamber will not over-deepen, the patient will feel no discomfort, and phaco can proceed as though the eye were not myopic. As stated previously, repeat these steps each time the eye is entered with irrigation.

IOL implantation. Whichever IOL is chosen for use, it should be able to be implanted using an unenlarged phaco wound and a wound-assisted technique. However, due to the lower scleral rigidity in myopic eyes, implantation may be difficult, as the counterpressure provided by the eye is lower. Accordingly, it is important to adequately fill the eye with OVD. The capsular bag should be filled first, followed by the rest of the anterior chamber. This creates two compartments within the eye and prevents the capsular bag from collapsing, which can make lens placement more difficult.

Wound closure. With good wound construction, there should not be difficulty in closure. However, due to the decreased scleral rigidity in myopic eyes, it is important to check the wounds for stability and leakage. If in doubt, do not hesitate to place a stitch.

With all the aforementioned caveats, it is still worth considering early surgery in myopes of this degree with cataract because the amount of visual disturbance is often disproportionate to the extent of cataract seen clinically.

Patient No. 2

preoperative considerations

A 35-year-old, -8.50 D myopic patient with healthy eyes will likely have expectations different from those of an older patient with cataract, as he or she will be making a lifestyle choice to become spectacle independent. Although excimer laser at this level of myopia is an option, results with phakic IOLs are probably more reliable. Refractive lens exchange in myopes of this degree with still functioning accommodation is not a sensible option. This can always be done at a later stage when the patient has become presbyopic, with the phakic IOL removed at the time of lens exchange.

As part of the preoperative work-up, if a phakic IOL is to be implanted, an endothelial cell count is mandatory wherever the lens is going to be placed. Of course, this must also be checked at regular intervals postoperatively. The lens must be assessed for any opacities and the retina for any retinal issues. In the present case, these are assumed to be normal.

There are several lens choices available to be positioned in front of, on, and behind the iris. I prefer to use the AcrySof Cachet anterior chamber IOL (Alcon Laboratories, Inc.). The company has an excellent calculator that has proven to be accurate. The sizing of these lenses is important, as well as the power, and anterior segment optical coherence tomography or Scheimpflug imaging is helpful in determining the sizing measurements. A lens that is too short or too long must be removed and replaced.

surgical procedure

Wounds. As with the older patient with cataract, wound construction is important in this patient. The lack of rigidity in the sclera will be even more apparent in this younger patient. It is important that, at the end of surgery and in the ensuing days, the anterior chamber does not leak and allow the anterior chamber to shallow. In this case, the wound must be 2.5 mm, as the mouth of the cartridge delivering the lens should be in the anterior chamber. If there is any doubt about wound closure, a stitch should be placed.

IOL implantation. The process of implanting the AcrySof Cachet is straightforward and unlikely to lead to complications. It is important to load the lens correctly with both feet pointing forward. The optic of the lens must be evenly folded in the cartridge so that it opens symmetrically inside the eye. After the wound is created, the eye is filled with OVD. It is best to use a cohesive OVD of sodium hyaluronate 1%, which can be easily removed at the end of the procedure. Do not overfill the eye and create a concave iris surface.

The lens cartridge is pushed across the anterior chamber, and the leading haptics emerge into the angle. The cartridge is gradually withdrawn across the anterior chamber as the lens emerges. Finally, the trailing haptics are placed (Figure 2). Check that the haptics are at neither too flat nor too acute an angle, as this will indicate incorrect sizing. If that is the case, the lens must be removed and a correct one placed. It is important to remove all of the OVD at the end of the procedure to avoid pupillary block by the lens.

Remember that myopic patients can get a sudden deepening of the eye when irrigation and aspiration is used. I recommend using a bimanual irrigation and aspiration and placing the aspiration in the main wound to allow easy egress of OVD without pressurizing the eye.

CONCLUSION

Moderately high myopes such as those described in this article require different treatment approaches, depending on patient age and other factors. By using the techniques illustrated above, both types of patients should achieve the visual results they desire with minimal risk of complications.

Richard Packard, MD, FRCS, FRCOphth, practices at the Prince Charles Eye Unit, King Edward VII Hospital, Windsor, England. Dr. Packard states that he no financial interest in the products or companies mentioned. He may be reached at e-mail: mail@eyequack.vossnet.co.uk.

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