High Myopia and Cataract Surgery

From EyeWiki


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 one eye undergoes surgery, the patient may experience significant anisometropia, or difference in refraction between the two eyes, prior to the second cataract surgery. If corrected for distance bilaterally, 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

Various studies have focused on the rate of complications in high myopes. Some studies have reported that intraoperative complications are not significantly increased with high axial length.[4] Several others have reported an increased risk. In a 2012 study, intraoperative complications increased 1.04-fold for each year of age increase, independent of refractive status. Complications increased 1.22-fold for every 1.0 mm increase in axial length.[9]
The following are estimated rates of intraoperative complications in high myopia:

  • Posterior capsule tear: 2.3-9.3% for axial length > 27.0 mm[4][9]
  • Zonular dehiscence: 1.7% for axial length > 30.0 mm[4]
  • Anterior capsule tear: 1.1% for axial length > 30.0 mm[4]

Highly myopic eyes are also at increased risk for anterior chamber depth fluctuations and lens-iris diaphragm retropulsion syndrome, characterized by 360 degrees of iridocapsular contact leading to reverse pupillary block, pupil dilation, and pain. Zonular weakness predisposes to this condition.[8][6]

Surgical Technique

The American Academy of Ophthalmology recommends several techniques for minimizing complications in the operating room:

  1. Ensuring adequate pressurization of the anterior chamber during capsulorrhexis with an ophthalmic viscosurgical device (OVD) to prevent capsule tears[8]
  2. Minimizing incision leakage and repeated collapse of the anterior chamber to prevent excessive movement of the iris and vitreous[8]
  3. Decreasing irrigating bottle height and increasing flow rate to avoid deepening the anterior chamber, which would make lens manipulation difficult[8][6]
  4. In the case of lens-iris diaphragm retropulsion syndrome and reverse pupillary block, using a spatula, cannula, or Sinskey hook to elevate the pupil margin to allow fluid to flow past the pupil[8][6]

Postoperative Management

Medications

Regardless of refractive status, surgeons usually prescribe topical steroids and NSAIDs to curb inflammation and decrease the risk of postoperative cystic macular edema (CME). Patients also usually use a topical fluroquinolone antibiotic.[3]

Late Complications

The highly myopic patient may be at increased risk of retinal detachment. Some studies have shown that the risk of retinal detachment increases with increasing axial length. In one study, an axial length > 26.0 mm was associated with a 0.9-3.8% risk of retinal detachment. Axial lengths of > 27.0 mm, > 29.0 mm, and 33.6-35.5 mm were associated with risks of 0.5-6.5%, 1.3-8.0%, and 11% respectively. Retinal breaks had an incidence of 1.1% for axial length greater than 30.0mm, and vitreous hemorrhage had an incidence of 0.6% for axial length greater than 30.0 mm.[4] In another study, uncomplicated eyes with high myopia had a 0.8% risk, while emmetropic eyes had a 0.4% risk.[2] In contrast, stome studies have shown no significant difference in the rates of retinal detachment in myopia compared to emmetropia.[10]

Refractive error is another potential complication, as hyperopic error appears to increase with axial length, especially in patients receiving a negative power lens. This phenomenon is most likely due to less accurate axial length measurement, especially in the presence of posterior staphyloma or poor fixation due to macular disease.[4] One study identified myopic degenerative changes as the single independent factor limiting final visual acuity.[11]

If a sulcus intraocular lens is inserted, it is also more likely to be unstable or decenter because of the larger sulcus size.[8]

Clinically significant macular edema (CSME) was found to have an incidence of 0.6% for axial length > 30.0 mm.[4]

The need for Nd:YAG capsulotomy for posterior capsular opacity (PCO) was demonstrated to be 31.6% for axial length > 30.0 mm versus 6.5-46.7% of the general population.[4]

Follow Up

Periodic dilated fundus exams to assess for retinal breaks are important in the postopertive management of the highly myopic patient.[3]

If the other eye has a cataract, timely surgery would be important to reduce the duration of anisometropia for the patient.[3]

Additional Resources

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 2.6 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 3.3 3.4 3.5 Devgan, U. Cataract Surgery for Patients With Myopia. Ophthalmology Management. http://www.ophthalmologymanagement.com/articleviewer.aspx?articleID=100823. Accessed September 28, 2014.
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 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. 6.0 6.1 6.2 6.3 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 8.2 8.3 8.4 8.5 8.6 8.7 High myopia and cataract surgery. American Academy of Ophthalmology. Practicing Ophthalmologists Learning System. http://one.aao.org/pols-snippet/2217. Accessed September 28, 2014.
  9. 9.0 9.1 Fesharaki H, Peyman A, Rowshandel M, Peyman M, Alizadeh P, Akhlaghi M, Ashtari A. A comparative study of complications of cataract surgery with phacoemulsification in eyes with high and normal axial length. Adv Biomed Res. 2012;1:67.
  10. Bernheim D, Rouberol F, Palombi K, Albrieux M, Romanet JP, Chiquet C. Comparative prospective study of rhegmatogenous retinal detachments in phakic orpseudophakic patients with high myopia. Retina. 2013;33(10):2039-48.
  11. Akar S, Gok K, Bayraktar S, Kaya V, Kucuksumer Y, Altan C, Yilmaz OF. Phacoemulsification in high myopia. Saudi Med J. 2010;31(10):1141-5.