Refractive Lens Exchange for Myopia Correction

Background

Clear lens extraction (CLE), also called refractive lens exchange (RLE), is the removal of a noncataractous natural lens of the eye with or without intraocular lens placement as a refractive procedure.

History of the Procedure

This refractive procedure has been around for nearly a century, and, throughout that time, it has been in a sea of controversy. In the past 5-10 years, CLE has slowly become accepted as a viable alternative to other refractive procedures for selected patients.

Problem

CLE is usually reserved for patients with high myopia (>8 diopters [D]) that is not easily managed by other refractive procedures, such as laser in situ keratomileusis (LASIK) or photorefractive keratoplasty (PRK). However, CLE may be an even better choice for patients with high hyperopia (>4 D) than for patients with myopia because of the smaller risk of postoperative retinal detachment and the fewer modalities available to treat patients with high hyperopia.

Epidemiology

Frequency

CLE still accounts for probably less than 1% of refractive procedures.

Etiology

Myopia is believed to be a result of a genetic predisposition in combination with close work over an extended period.

Pathophysiology

Myopia is due to an axial length longer than the focal point of the refracting system of the eye or an overly powerful refracting system, a thick cornea, or a thick lens, or a combination of any or all of the above.

Presentation

Myopia usually develops in early or mid teens and stabilizes in early adulthood. It presents as blurry distant vision.

Indications

Optical or refractive indications for lens surgery are ametropia (ie, myopia, hyperopia, astigmatism), anisometropia, and presbyopia. These include all classic refractive states of the healthy adult eye, which is why this new indication for lens surgery is controversial; no true histopathology may exist in most of these eyes.

Some eyes, as in those with extreme axial myopia, may be at risk for true pathology following surgical intervention. In addition, historical development of spectacles and contact lenses antedates the development of modern lens surgery. For these reasons, a mind-set has been created among academics that inborn errors of refraction are not diseases; therefore, they are not conditions to be treated by medicine or surgery, especially if such treatment might unnecessarily endanger an eye or expose an otherwise healthy eye to undue risk. This argument is rapidly losing credence.

The global anterior segment ophthalmic surgical community has embarked on a new and enticing endeavor called human emmetropia worldwide. The process began as an "idea before its time" in the 1950s, with the failed attempts at endothelial radial keratotomy of Barraquer and others at phakic anterior chamber intraocular lens (IOL) implantation.

The ophthalmic surgical technical revolution that ensued over the following decades allowed a return to the concept of the surgical correction of refractive errors 30 years later in the 1980s, this time as an "idea whose time had come." Refinements in ocular anesthesia, incision technology, lensectomy techniques, viscoelastic tissue protection, and IOL manufacture and implantation resulted in a return to the concept of intraocular correction of refractive errors, which includes both clear lensectomy and phakic implantation [1. All this, combined with the seeming multitude of new keratorefractive procedures, led to the development of a new bona fide ophthalmic surgical subspecialty, controversial as it may appear, called refractive surgery.

The basic needs of refractive surgery are accuracy, stability, safety, and quality of vision.

Regarding accuracy, ideally, a standard deviation of less than 0.25 D is wanted, yielding 20/25 (or better) uncorrected acuity in 95% of patients for all amounts of myopia, hyperopia, and astigmatism. Currently, no procedure produces this result, but the closest are still LASIK or PRK for patients with low or moderate myopia and LASIK for patients with mild hyperopia. Currently, A-scan measurements and IOL choice, even using the IOL Master, especially in patients with high hyperopia and those with myopia, yield an accuracy of significantly less than ± 0.25 D.

For stability, CLE is probably the most stable refractive procedure available, with ± 0.02 D per year reported over a 9-year observation period. PRK has a significantly higher risk of regression or progression, and, in addition, LASIK carries a risk of corneal ectasia.

Several studies have shown that, for quality of vision, an unoperated cornea is optically superior to an operated cornea. Any operation on the cornea creates abnormal contours, which, in turn, create optical aberrations. The greater the correction, the greater the amount of induced aberration and the concurrent decrease in quality of vision, especially in low-contrast situations (eg, driving at night). Clearly, CLE is an optically superior choice in some situations.

Safety is discussed more extensively below.

Without question, the consequences of some complications (eg, endophthalmitis, retinal detachment) of intraocular surgery are much graver than the worst complications (eg, flap loss, corneal scarring requiring corneal transplant) of other refractive procedures.

Almost all operable tissues and spaces of the eye, including the corneal surface, the corneal stroma, the anterior chamber, the pupil, the posterior chamber, the lens, and the sclera, have been investigated as locations for refractive surgical modulation. Therefore, among others, the lens assumes its role as a popular location for surgical refractive modulation for those who prefer a familiar procedure that not only spares the cornea but also saves the economic expense of an excimer. Those who decry the lenticular approach emphasize all potential intraoperative and postoperative complications attendant with invasive intraocular procedures.

Despite the controversy, clear lens replacement is a viable procedure for both myopia and hyperopia, and toric IOLs are now available for intraocular correction of astigmatism. Multifocal IOLs and accommodative IOLs are now being used by many surgeons for the intraocular correction of presbyopia. Other attempts at development of a truly accommodative pseudophakos include intracapsular injection of liquid silicone, intracapsular placement of high-water content poly-HEMA lenses, liquid silicone-filled intracapsular balloon, multiple IOL implantation, polypseudophakia, and intracapsular placement of a flexible, plate-haptic, foldable, accommodative IOL.

Once thought of as an "idea before its time," surgical restoration of accommodation is becoming more of a reality. In 2003, the US Food and Drug Administration (FDA) approved the intracapsular placement of a flexible, plate-haptic, foldable, accommodative IOL, called Crystalens, for patients with cataracts. Crystalens was the first IOL to allow patients to focus on objects both at near and at distance without the use of spectacles or contact lenses. Working much like the natural lens of the eye, Crystalens, with its hinged haptics, facilitates back and forth movement along the optical axis of the eye in response to pressure changes that result from ciliary muscle relaxation and contraction. Since that early Crystalens, newer and improved versions have come out, and competitive brands with different modalities, such as ReSTOR [2and ReZoom, have also entered the marketplace.

The surgical reversal of presbyopia is refractive surgery's "final frontier." Clinicians are exploring different techniques to surgically treat/reverse presbyopia (see Surgical Reversal of Presbyopia: A Comprehensive Video Text).

Indications for CLE are currently seen as the following:

  • Myopia when other refractive procedures are contraindicated

  • Myopia when other refractive procedures would give an inadequate result

  • Hyperopia when other refractive procedures are contraindicated

  • Hyperopia when other refractive procedures would give an inadequate result

Relevant Anatomy

CLE is performed as any other cataract procedure; the only difference is the decreased use or absence of phacoemulsification power and the almost exclusive use of aspiration. [3]

Ideally, this procedure is performed using a clear cornea approach, making a 3-mm or smaller corneal incision, creating a regular capsulorrhexis, performing aspiration within the bag, and placing an IOL of choice in the bag.

Contraindications

Contraindications include retinal disease. With high myopia, a higher rate of retinal detachment exists than with other types of refractive errors.

Prognosis

The prognosis is excellent.



Laboratory Studies

The usual preoperative workup as for cataract extraction is recommended.

Protocol varies from facility to facility and may include a chest x-ray, an ECG for patients older than 40 years, glucose and electrolyte studies, and a CBC count.

If patients are on blood thinners, prothrombin time (PT)/active partial thromboplastin time (PTT) or bleeding time may also be ordered.

Imaging Studies

A-scan biometry and IOL Master are recommended to determine the best power of IOL to be placed.

Using indirect ophthalmoscopy, a detailed examination of the peripheral retina must be undertaken, especially in patients with high myopia, to look for abnormalities (eg, lattice, holes, tears).

Other Tests

See Lab Studies.


Medical Therapy

Essentially, most ophthalmologists should follow their standard protocol for cataract extraction.

Consideration should be given to antibiotic prophylaxis beforehand (eg, Ocuflox qid 1 day preoperatively).

Preoperative prophylactic treatment of the peripheral retina, especially in patients with preexisting abnormalities and in those with high myopia, should be considered. So far, published results on CLE have shown that prophylactic 360° laser therapy provides a lower incidence of postoperative detachment than direct treatment limited to the visible abnormalities, which shows little difference from no treatment at all.

Topical antibiotics and steroids, separately or in combination, should be used postoperatively.

Prednisolone acetate 1% (Pred Forte)

Sterile ophthalmic suspension that is a topical anti-inflammatory agent for treating steroid responsive inflammation of the palpebral and bulbar conjunctiva, corneal and anterior segment.

Adult dose: Instill 1-2 gtt 2-4 times/d into conjunctival sac; during initial 24-48 h, dosage may be increased in frequency prn; shake well prior to use; do not discontinue therapy prematurely

Pediatric dose: Not established

Contraindications: Documented hypersensitivity; contraindicated in most viral diseases of the cornea and the conjunctiva, including epithelial herpes simples keratitis (dendritic keratitis), vaccinia, and varicella, and also in mycobacterial infection of the eye and in fungal diseases of ocular structures; prolonged use may lead to glaucoma and cataracts

Pregnancy: Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus.

Precautions: Fungal infections of the cornea are prone to develop coincidentally with long-term local corticosteroid use; suspect fungal invasion in any persistent corneal ulceration where a corticosteroid has been used or is in use; obtain fungal cultures when appropriate; if used for 10 d or longer, monitor intraocular pressure.

Ciprofloxacin 0.3% (Ciloxan Ophthalmic, Cipro)

Adult dose: 1 gtt q30min for 12 doses, then 1 gtt qh for the first 24-48 h; gradually taper off according to the clinical course

Pediatric dose: Administer as in adults

Pregnancy: Fetal risk not revealed in controlled studies in humans.

Precautions: May inhibit reepithelialization by crystallizing over the epithelial defect

Surgical Therapy

Essentially, surgeons should follow their standard cataract procedure, making allowances for the softer lenses.

Preoperative Details

One standard procedure is as follows:

  • Ocuflox qid for 1 day preoperatively

  • Mydriacyl 1%, 3 sets separated by 10 minutes, 1 hour preoperatively

  • Betadine 5-10% ophthalmic solution, 2 drops to cul-de-sac before starting procedure

Intraoperative Details

CLE is similar to cataract surgery, except less ultrasound and more aspiration are used.

Postoperative Details

Consider Miochol or postoperative pilocarpine if not contraindicated.

Follow standard protocol for postoperative medication. One recommended protocol is as follows:

  • Ocuflox 1 gtt qid for 10 days (or until the bottle runs out)

  • Pred Forte 1 gtt qid for 4 days, then taper to 1 gtt every 4 days until discontinued

Follow-up

Postoperative follow-up care is arranged with patients on day 1, at 1 week, and at 1 month, at which point refraction may usually be performed.

Follow-up care is similar to that for cataract surgery, with attention given to the same possible complications. Patients and/or their caregivers are instructed to call the ophthalmologist if vision suddenly deteriorates instead of slowly improves, if pain occurs, or if the eye becomes red or inflamed.

Complications

Complications include the following:

  • Posterior capsular opacification

  • Retinal detachment

    Comparison of published data on retinal detachmentComparison of published data on retinal detachment after clear lens extraction.
  • Macular edema

  • All of these complications are particularly prevalent in cases of extreme refractive error; macular edema is more common in patients with hyperopia.

The remaining complications are the same as for any cataract surgery; a detailed discussion can be found in Cataract, Senile.

  • Endophthalmitis

  • Corneal edema from endothelial disruption, vitreous touch

  • Wound distortion or disruption, leading to astigmatism and iris prolapse

  • Shallow or flat anterior chamber

  • Glaucoma

  • Uveitis

  • Intraocular lens dislocation

  • Hemorrhage (anterior segment or vitreous)

  • Capsular rupture or zonular dialysis

  • Corneal melting with ocular surface disease

  • Filtering bleb

  • Hypotony

  • Iridodialysis

  • Malignant glaucoma

  • Retained lens material

  • Suprachoroidal hemorrhage or effusion (particularly in patients with hyperopia)

  • Wound leak

  • Retinal light toxicity

  • Wrong power IOL

Outcome and Prognosis

Visual outcome is usually excellent.

A 2008 retrospective study of 129 eyes showed CLE with posterior chamber IOL implantation to be safe, predictable, and effective. CLE was shown to achieve excellent visual acuity and refractive outcome with few complications. [4]

The latest reports with prophylactic 360° therapy of peripheral retina show a statistically lower rate of retinal detachment in those eyes than if they had not been subjected to prophylactic treatment.

Future and Controversies

CLE is becoming a more accepted procedure. Arguments in favor of CLE are as follows: predictability, stability, ease and cost with which a general surgeon can perform the technique, use of toric or multifocal lens technologies and small-incision surgery, and better optical quality vision. Arguments against CLE are as follows: seriousness of complications, rate of complications, and availability of other less invasive refractive procedures.

In a 2004 study comparing the 2 procedures, Arne believed that phakic IOL placement was a safer modality than CLE in the same selected group of patients that corneal refractive surgery cannot address. [5]

If clouding of the capsule can be eliminated and if a truly accommodating and adjustable lens can be achieved, CLE could become a much more prevalent refractive procedure.

The advent of the ReSTOR and ReZoom lenses in 2005 and 2006, respectively, increased the frequency of this procedure, and the advent of newer and better lenses continues to increase demand and quality of results.

Studies from 2010 show that CLE is a also a financially better and easier modality for treating high myopia in the developing world and that supracapsular phacoaspiration for clear lens extraction in correction of high myopia seems to present no risk for the posterior capsule, although there is a marginal risk to the endothelial cell count. 

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