High Myopia and Cataract Surgery

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Epidemiology

Myopia is highly prevalent in the general population, affecting approximately 25%. It affects a larger proportion of Asians and a smaller proportion of African Americans. High myopia affects about 2% of the population. High myopia refers to a spherical equivalent of -6.0 D or less or an axial length of 26.5 mm or more. Pathologic myopia refers to a spherical equivalent of -8.0 or less or an axial length of 32.5 mm or more.[1]

According the the Beaver Dam Eye Study and the Blue Mountains Eye Study, there is an association between myopia and nuclear cataract. The Blue Mountains Eye Study also found that moderate and high myopia, especially with onset prior to age 20, are associated with posterior subcapsular cataract formation.[2]

Preoperative Evaluation

Patient Expectations

It is important to have a thorough discussion with the highly myopic patient about setting realistic goals and expectations regarding cataract surgery outcomes. If corrected for distance, patients should be advised that they will experience more difficulty with near vision. Some may opt for monovision in order to maintain the ability to see up close.[3] If the patient has undergone prior refractive surgery, it is important to evaluate the prior refractive status and obtain previous records.[2] Furthermore, increased age and axial length have both been associated with a negative effect on best corrected visual acuity. An estimated 62% of myopic eyes have some degree of myopic or age-related retinal degeneration.[4]

Risks and Informed Consent

Two of the most commonly discussed cataract surgery risks for highly myopic patients are increased risk of retinal detachment and variable postoperative refractive error. The cataract surgeon may choose to include an evaluation by a vitreoretinal specialist prior to cataract surgery, but this practice is controversial and not universally adopted.[2] Please see the section entitled Late Complications for a more in depth discussion of these risks.

IOL Calculations

One of the difficulties with preoperative calculations in highly myopic patients is the determination of axial length. As axial length increases, measurements may become less reliable. An estimated 70% of eyes with axial length greater than 33.5 mm are estimated to have posterior staphylomata, or localiazed ectasia of the sclera, choroid, and retinal pigment epithelium. However, almost all eyes with pathologic myopia are thought to have some degree of posterior staphylomata.[2][1] 

Not all experts agree on the best method to measure axial length. According to some sources, if a patient is able to fixate on a target, automated biometry such as the IOL Master (Carl Zeiss Meditec) may be able to estimate the patient's refractive axial length, from the corneal vertex to the fovea, with fairly high accuracy.[2] In other studies, the IOL Master was found to underestimate the power of the IOL for eyes with axial length > 27.0 mm and eyes receiving a negative power IOL.[4] In addition, A-scan contact and immersion biometry measures the anatomical axial length, from the corneal vertex to the posterior pole, and may overestimate axial length in the presence of staphylomata, leading to unexpected hyperopia.[2] 

There is also controversy over which formula is the best for calculating IOL power. Traditionally, the SRK/T, a third generation formula, is thought to be an accurate formula for patients with high axial length.[4][3] In a 2012 study, however, the Haigis formula was found to be superior to the SRK/T, SRK II, and Holladay I. 81% of eyes had refractive error within 1.0 D of predicted, and 54% were within 0.5 D of predicted using the Haigis formula. In contrast, 59.5% of eyes were within 1.0 D of predicted, and 29.7% were within 0.5 D of predicted using the SRK/T formula.[5] Still, the third generation (Holladay I, Hoffer Q, SRK/T) and fourth generation (Haigis, Holladay II) formulas may all tend to overminus IOLs in patients with high myopia.[4]

IOL Selection

When possible, it is advisable to place an IOL rather than leave a highly myopic patient aphakic. The IOL acts as a barrier to vitreous movement and subsequent retinal traction. If the patient may undergo future retinal surgery, an acrylic lens implant would be preferable to a silicone lens.[6] 

Given the relatively high incidence of postoperative hyperopia in patients receiving a negative power IOL, the surgeon may aim for a myopic target refraction around -2.0 D in this case.[4]

Several lens options are available for the highly myopic patient, including the following:[3]

  • P574UV PMMA Non-Foldable IOL (Bausch & Lomb, Rochester, NY): down to -18.9
  • Sensar AR40M Acrylic IOL (Abbott Medical Optics [AMO], Santa Ana, CA): -10.0 to +1.5 D[7]
  • AQ5010V Silicone IOL (STAAR, Monrovia, CA): down to -4.0 D
  • Acrysof Acrylic IOL (Alcon, Fort Worth, TX): down to -5.0 D
  • SofPort Silicone IOL (Bausch & Lomb, Rochester, NY): down to 0.0 D
  • Crystalens Five-O (eyeonics, Aliso Viejo, CA): down to 3.0 D

Perioperative Period

Anesthesia

Retrobulbar and peribulbar anesthesia carry the risk of perforation of the globe in a long, myopic eye.[8]

Topic anesthesia is safer, but the patient may experience more discomfort due to iris movements during surgery.[8]

Intraoperative Complications

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Surgical Technique

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Postoperative Management

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Medications

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Follow Up

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Late Complications

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Additional Resources

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References

  1. 1.0 1.1 Basic Clinical and Science Course. Retina and Vitreous. 2013-14. Section 12 pg 85-86.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Dodick, JM, Kahn JB. Special Considerations for Cataract Surgery in the Face of Pathologic Myopia. In: Spaide, RF, Ohno-Matsui, K, Yannuzzi, LA, eds. Pathologic Myopia. New York, NY: Springer Science+Business Media; 2014:313-314.
  3. 3.0 3.1 3.2 Devgan, U. Cataract Surgery for Patients With Myopia. Ophthalmology Management. http://www.ophthalmologymanagement.com/articleviewer.aspx?articleID=100823. Accessed September 28, 2014.
  4. 4.0 4.1 4.2 4.3 4.4 Zuberbuhler B, Seyedian M, Tuft S. Phacoemulsification in eyes with extreme axial myopia. J Cataract Refract Surg. 2009;35(2):335-40.
  5. Roessler GF, Dietlein TS, Plange N, Roepke AK, Dinslage S, Walter P, Mazinani BA. Accuracy of intraocular lens power calculation using partial coherence interferometry in patients with high myopia. Ophthalmic Physiol Opt. 2012;32(3):228-33.
  6. Basic Clinical and Science Course. Lens and Cataract. 2013-14. Section 11 pg 200.
  7. Sensar IOL with OptiDdge Design. http://www.precisionlens.net/site/pdfs/AMO%20AR40%20Spec%20Sheet.pdf. Accessed September 28, 2014.
  8. 8.0 8.1 High myopia and cataract surgery. American Academy of Ophthalmology. Practicing Ophthalmologists Learning System. http://one.aao.org/pols-snippet/2217. Accessed September 28, 2014.


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