Cataract Surgery, 3rd Edition

PART V – Special Techniques for Cataract Extraction

Chapter 32 – High Myopia

Roger F. Steinert, MD


Contents

  

   

Preoperative Evaluation

  

   

Intraoperative Considerations

  

   

Postoperative Care

CHAPTER HIGHLIGHTS

  

   

Surgical challenges of long eye and deep anterior chamber

  

   

Complications associated with high myopia

  

   

Special surgical techniques in high myopia

Cataract surgery in the presence of high axial myopia poses a number of challenges for the surgeon. Special consideration must be given to these patients at each stage of the preoperative, operative, and postoperative periods. Table 32-1 summarizes these key considerations in high myopia.


Table 32-1   -- Special elements in cataract surgery for high myopia

Preoperative

Peripheral retina exam

Macular exam

Potential acuity testing

Biometry, postoperative refractive goal determination, and IOL power calculation

Intraoperative

Risk of retrobulbar/peribulbar anesthetic injection

Increased anterior-chamber depth

Reduced nuclear support

Postoperative

Preservation of a clear posterior capsule/capsulotomy complications minimized

Surveillance for peripheral retinal breaks/early detection of retinal detachments

 

Preoperative evaluation

A comprehensive preoperative evaluation is performed on all cataract patients. In the case of high axial myopia, however, the surgeon must pay particular attention to the fundus exam. High myopia is associated with a higher risk of both peripheral and macular retinal pathologic conditions. Measurement of macular visual potential is important if there is disturbance of the pigment epithelium or evidence of atrophy or neovascularization from the choroid. Preoperative evaluation of potential visual acuity is covered in Chapter 3.

The peripheral retina in high axial myopia is more vulnerable to pathologic conditions that increase the risks of retinal detachment. A careful preoperative peripheral retinal examination is mandatory. However, visualization of the peripheral retina, even with aggressive scleral depression, may not reveal preexisting peripheral retinal pathologic conditions because of impaired visualization caused by the cataract.

The other primary challenge facing the cataract surgeon preoperatively, in the presence of high myopia, is determination of the intraocular lens (IOL) power. First, the accuracy of the A-scan biometry and the subsequent calculation of the IOL power are subject to more variability in high myopia than in patients with a normal-sized eye. If the axial myopia is accompanied by a posterior staphyloma, the precise determination of the axial length at the fovea is often imprecise.

Even with an accurate determination of the axial length, the IOL power formulas have less accuracy in the more extreme ranges. Studies have indicated that the SRK-T formula is more accurate in high axial myopia than other formulas (see Hoffer KJ [1993] and Holladay JT [1998] in Further Reading and Chapter 4). Even then, however, there is considerably more variability in the IOL power accuracy in these cases.

The surgeon must discuss with the patient the intended postoperative IOL power goal. While some myopes value excellent distance uncorrected vision, other myopes have enjoyed the ability to read with spectacles. Determining the desired postoperative refractive goal is a key step in the preoperative surgical planning.

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Intraoperative considerations

High axial myopia poses a high risk of complication with retrobulbar or peribulbar anesthesia. The larger and longer globe fills more of the orbit, and the passage of a needle posteriorly is more prone to inadvertently penetrating the sclera. Moreover, the sclera in high axial myopia is thinner, resulting in less resistance to penetration by an anesthetic injection needle (see Chapter 8).

High myopes typically have deeper anterior chambers and less residual formed vitreous than the average patient. Therefore, the surgeon may face excessive anterior chamber deepening on introducing the phacoemulsification tip and irrigation. If so, the height of the infusion bottle should be lowered. There may also be more mobility of the nucleus, related both to zonular laxity and the lack of vitreous support. The vitreous body is frequently more liquefied than in a similar-aged emmetrope. As a result, the surgeon should expect to face a deeper anterior chamber and more anteroposterior movement of the crystalline lens and capsule in the course of the phacoemulsification. Moreover, there is less vitreous support for the posterior capsule, and many surgeons have observed that the posterior capsule has the potential for rupturing during surgery at a higher rate in high axial myopia. Furthermore, if the posterior capsule does rupture, the liquefied vitreous will not provide normal resistance to posterior migration of nuclear fragments. The patient is, therefore, at higher risk for loss of nuclear fragments into the deep vitreous and against the retina. Should this complication occur, the anterior-segment surgeon should obtain the assistance of a skilled vitreoretinal surgeon in the safe removal of the nuclear fragments. If a vitreoretinal surgeon is available, this can be done immediately in the course of the cataract surgery. If not, then the cataract surgeon should complete the anterior cleanup and obtain an immediate postoperative consultation to schedule the patient for an expeditious removal of the posterior lens fragments by the vitreoretinal surgeon.

In the presence of this complication, a frequently debated issue is whether the cataract surgeon should place the IOL primarily or whether the patient should be left in an aphakic state. If the nuclear fragments that remain are quite large and dense, a vitreoretinal surgeon may choose to bring the fragments up through the pupil and deliver them through a limbal incision, rather than attempt a posterior ultrasonic fragmentation of a very large and dense nucleus. If the nuclear fragments are reasonably small, however, the vitreoretinal surgeon will usually feel comfortable with posterior ultrasonic fragmentation of the remaining nucleus. In that case, the presence of an IOL will not impede the vitreoretinal surgeon's maneuvers. Ideally, a cataract surgeon should develop a good working relationship with a vitreoretinal surgeon and explore the vitreoretinal surgeon's preferences regarding IOL placement under these circumstances.

High axial myopia presents one other challenge for a surgeon who wishes to perform surgery through a corneal scleral incision rather than a limbal or fully clear corneal incision. In true high axial myopia, the sclera may be markedly thinned. The surgeon needs to anticipate that dissection should be more shallow than usual to avoid inadvertent penetration through the sclera onto the ciliary body while attempting to dissect a scleral tunnel incision.

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Postoperative care

Maintaining the integrity and clarity of the posterior capsule is generally regarded as important in reducing the frequency of vitreoretinal complications. In addition, a broad area of clear posterior capsule and a large optic assist in the examination of the patient's retina postoperatively. A pupil that is not traumatized during surgery and does not have postoperative synechia inhibiting dilation also contributes to good postoperative care. Therefore, the cataract surgeon should use a meticulous technique with a centered capsulorrhexis, thorough cortical cleanup, and great care to maintain the integrity and clarity of the posterior capsule. The choice of IOL should be influenced by these considerations.

A large optic, either 6 or 6.5mm, is preferable to a smaller optic. Using an IOL optic material that will interfere least with subsequent vitreoretinal surgery, if needed, and an IOL optic edge that is configured to inhibit posterior capsule opacification is recommended. Currently, the lens of choice in this circumstance has a square or modified square edge (see Chapter 37).

Because the high axial myopic patient is at higher risk for retinal detachment, it is advisable to carefully examine the peripheral retina with wide dilation and scleral depression with indirect ophthalmoscopy early postoperatively, such as several weeks, but also to perform such an examination at more frequent intervals. Many postoperative detachments do not occur for many months or years after the surgery. If there is difficulty in visualization of the peripheral retina or a question about the advisability of “prophylactic” laser treatment of suspicious peripheral lesions, consultation with a vitreoretinal surgeon is recommended (see Chapter 56).

If the posterior capsule opacifies to the point of functional visual impairment, then Nd:YAG laser posterior capsulotomy may be indicated. To minimize the disturbance to any residual formed vitreous and to maintain as much integrity of the barrier function of the capsule–IOL complex, the surgeon is advised to use the lowest amount of energy necessary to open the posterior capsule and to keep the size of the capsular opening smaller than the optic (see Chapter 51).

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Further Reading

Alldredge C.D., Elkins B., Alldredge O.C.: Retinal detachment following phacoemulsification in highly myopic cataract patients.  J Cataract Refract Surg  1988; 24:777-780.

Apple D.J., Solomon K.D., Tetz M.R., et al: Posterior capsular opacification.  Surv Ophthalmol  1992; 37:73-115.

Buratto L.: Phacoemulsification: principles and techniques,  Thorofare, NJ, Slack, 1988.

Buratto L., Buratto L.E.: Cataract surgery in axial myopia,  Milano, Ghedini, 1994.

Coonan P., Fung W.E., Webster R.G., et al: The incidence of retinal detachment following extracapsular cataract extraction: a ten year study.  Ophthalmology  1985; 92:106.

Curtin B.J.: The myopias: basic science and clinical management,  Hagerstown, Harper and Row, 1985.

Francois J.G., Goes F.: Comparative study of ultrasonic biometry of emmetropes and myopes, with special heredity of myopia.  Biometrie Oculaire Clinique Parigi  1976.Masson

Hoffer K.J.: The Hoffer Q formula: a comparison of theoretic and regression formulas.  J Cataract Refract Surg  1993; 19:700-712.

Hoffman P., Pollock A., Oliver M.: Limited choroidal hemorrhage associated with intracapsular cataract extraction.  Arch Ophthalmol  1984; 102:1761-1765.

Holladay J.T.: IOL power calculation for the unusual eye.   In: Gills J.P., Fenzyl R., Martin R.G., ed. Cataract surgery: the state of the art,  Thorofare, NJ: Slack; 1998:197-205.

Hollick E.J., Spalton D.J.: The effect of capsulorrhexis size on posterior capsule opacification,  1997.

Hollick E.J., Spalton D.J., Ursel P.G., et al: Lens epithelial cell regression on the posterior capsule with different intraocular lens material.  Br J Ophthalmol  1998; 82:1182-1188.

Hymans S.W., Bialik M., Neumann E.: Myopia-aphakia.  Br J Ophthalmol  1975; 59:480.

Jaffe N.S., Clayman H.M., Jaffe M.S.: Retinal detachment in myopic eye after intracapsular and extracapsular cataract extraction.  Am J Ophthalmol  1984; 97:48-52.

Koch P.S.: Phacoemulsification in patients with high myopia.  Phacoemulsification in difficult and challenging cases,  New York: Thieme Medical Publishers; 1999.

Osterlin S.: Vitreous changes after cataract extraction.   In: Freeman H.M., Hirose T., Schepens C.L., ed. Vitreous surgery and advances in fundus diagnosis and treatment,  New York: Appleton-Century Crofts; 1977:15-21.

Percival S.P.B.: Long term complications from extracapsular cataract surgery.  Trans Ophthalmol. Soc UK  1985; 104:915-918.

Praeger D.L.: Five years' follow-up in the surgical management of cataracts in high myopia treated with the Kelman phacoemulsification technique.  Ophthalmology  1979; 86:2024-2033.

Retzlaff J.: A new intraocular lens calculation formula.  J Am Intraocul Implant Soc  1980; 6:148-152.

Retzlaff J.A., Sanders D.R., Kraff M.C.: Development of the SRK/T intraocular lens implant power calculation formula.  J Cataract Refract Surg  1990; 16:333-340.

Rickman-Barger L., Florine C.W., Larson R.S., et al: Retinal detachment after neodymium YAG laser capsulotomy.  Am J Ophthalmol  1989; 107:531-536.

Sanders D.R., Retzlaff J., Kraff M.C.: Comparison of empirically derived and theoretical aphakic refraction formulas.  Arch Ophthalmol  1983; 101:956-967.

Selley L.F., Barraquer J.: Surgery of the ectopic lens.  Ann Ophthalmol  1973; 35:1127.

Shah G.R., Gills J.P., Durham D.G., et al: Three thousand YAG laser posterior capsulotomies: an analysis of complications and comparison to polishing and surgical discission.  Ophthalmic Surg  1986; 17:473-477.

Ursell P.G., Spalton D.J., Pande M.V., et al: The relationship between intraocular lens biomaterials and posterior capsule opacification.  J Cataract Refract Surg  1998; 24:352-360.