Clear Lens Replacement Refractive Surgery
CHAPTER CONTENTS
We evaluate refractive surgical procedures with five basic criteria.
- predictability [the percentage of eyes within a certain dioptic range from the target refraction (e.g., ±0.5 D)]
- accuracy [the percentage of eyes achieving a certain level of uncorrected visual acuity (e.g., 20/25 or better uncorrected)]
- stability of refraction over time
- safety [the percentage of eyes losing lines of best corrected visual acuity (BCVA) after a refractive procedure]
- quality of vision postoperatively
The clinician may find that this procedure is the best option; however, the clinician must evaluate the facts of each case and each patient’s medical history to determine the most appropriate technique to use. The easiest and least invasive procedure may not necessarily be the best in terms of visual outcome.
Advantages
- high predictability and accuracy of refractive surgical result
- high level of safety
- very low incidence of lost lines of BCVA
- stability of postoperative refraction
- high quality of vision (does not alter the physiologic prolate corneal shape, thus avoiding potential iatrogenically induced aberrations)
- over 20 years of experience with technology (cataract surgery)
- a high level of experience and comfort with the technical aspects of the procedure for most surgeons
- greater predictability and postoperative visual quality for extreme refractive errors
- potential for treatment of eyes with low to moderate astigmatism (LASIK possible for any residual refractive errors)
Disadvantages
- loss of accommodation by the crystalline lens
- need for an intraocular surgical facility
- increased risk for intraocular complications
- endophthalmitis
- intraocular inflammation
- corneal endothelial damage
- retinal detachment
- blindness
- limitations of the low powers of intraocular lenses (IOLs) that are available for extreme myopia
- need for piggyback IOL insertion for extreme hyperopia
- corneal endothelial damage
PREOPERATIVE CONSIDERATIONS
Indications
- early or frank crystalline lens cataract formation that may require cataract extraction in the near future
- certain presbyopic or prepresbyopic patients
- high hyperopia
- myopia
- thin cornea
- extremely flat myopic cornea (<40 D corneal power)
- extremely steep hyperopic cornea (>49 D corneal power)
- reasonable patient expectations
Patient Evaluation
- measurement of visual acuities (monocular and binocular corrected and uncorrected distance and near vision)
- refraction and retinoscopy
- quantification of BCVA
- determination of any visual loss because of cataract formation
- identification of opacity or irregularity of the crystalline lens (e.g., posterior lenticonus) from lens changes
- determination of the potential acuity measurement (PAM) (If the cornea is without pathology, a discrepancy between PAM acuity and manifest refraction BCVA suggests a crystalline lens cataract.)
- topography and keratometry
- comparison of corneal astigmatism with lenticular and globe astigmatism
- calculation of lens power
- determination of placement, number, and length of limbal relaxing incisions (see Chapter 8)
- slit lamp examination
- identification of corneal disease and anterior segment pathology (if present)
- evaluation of corneal thickness (must be consistent in area of limbal relaxing incisions)
- A-scan
- preferably immersion instead of contact A-scan for greater accuracy
- a noncontact laser A-scan (e.g., a Humphrey Eye Master; Alcon, Fort Worth, TX) may surpass an immersion A scan because it is extremely accurate to a hundredth of a millimeter
- preferably immersion instead of contact A-scan for greater accuracy
- lens power calculation (measurements of axial length and anterior chamber depth required, depending on the lens power equation)
- measurement of intraocular pressure (IOP) for baseline evaluation and comparison with any postoperative increase in pressure
- dilated fundus (rules out conditions that may affect surgical outcome)
- pseudoexfoliation syndrome (weak zonules)
- peripheral retinal pathology (e.g., tears, holes, or lattice)
- prophylactic laser photocoagulation to any retinal holes (reduces postoperative risk for retinal detachment)
- prophylactic peripheral barrier laser photocoagulation (“retinal cerclage”; 2–3 rows of 300-400 burns for 360 degrees in the peripheral retina) for high myopics
- focal treatment of any inner retinal pathology associated with increased risk for retinal detachment
- no detachments reported by Centurion up to 7 years postoperatively among 35 patients with axial lengths >26.5 mm
- preparation and patient completion of informed consent form
- no detachments reported by Centurion up to 7 years postoperatively among 35 patients with axial lengths >26.5 mm
Lens Selection
SINGLE-PIECE POLYMETHYLMETHACRYLATE LENS The polymethylmethacrylate (PMMA) lens is the gold standard of IOL technology and has been used successfully for more than 20 years.
Advantages
- available in virtually all needed powers
- proven and dependable optics
- monovision a practical option
- excellent centration and stability within the capsular bag
- very inexpensive
Disadvantages
- need for limbal relaxing incisions for astigmatic treatment
- need for scleral tunnel approach
- high incidence of posterior capsular opacification (20-30%) requiring yttrium-aluminum-garnet (YAG) capsulotomy
FOLDABLE LENS Silicone, acrylic, and hydrogel lenses are currently available. Cataract surgeons prefer this lens because it allows small self-sealing (sutureless) incisions.
Advantages
- small size (≤ 3 mm) of corneal entry incision that is astigmatically neutral
- quickness of procedure
- ease of postoperative stabilization
- ability to reduce corneal or globe astigmatism by implanting a TORIC IOL (model no. AA4203-TL and AA4203-TF; Staar Surgical Company, Monrovia, CA)
- plate haptic design with cylindrical correction incorporated in its design
- currently available in 3.5 and 2.0 D powers that correct 2.4 and 1.4 D of corneal astigmatism (other powers under investigation)
- spherical powers available from 9.5 to 30 D
- lower incidence of posterior capsular opacification (2-3%; particularly for acrylic IOLs)
Disadvantages
- most experience with this lens gained over the last 5 years
- difficult management (if silicone oil required for complicated retinal detachment procedures) of movement with silicone lenses (after YAG laser capsulotomy)
- instability compared with the one-piece PMMA lens
- need for corneal refractive surgery to eliminate myopia (if patient unable to tolerate monovision)
- smaller range of IOL powers available for extreme high myopia and hyperopia compared with range for PMMA IOLs
- more expensive
MULTIFOCAL LENS The Medical Ophthalmics SIN40 lens (AMO ARRAY IOL; Allergan, Irvine, CA) is available in +10 to +30 D in increments of 0.5 D.
Advantages
- ability of both eyes to function at all distances (near, intermediate, and far)
- focused binocular visual function at each focal length
- less or no dependence on prescription spectacles postoperatively
- has all the advantages of other foldable IOLs
Disadvantages
- problems in mesopic and scotopic conditions
- glare or haloing
- inability to function in visually demanding situations
- patient dissatisfaction with subjective symptoms (e.g., night glare, distortions) that necessitates explantation and implantation of a monofocal lens
- glare or haloing
ACCOMMODATING INTRAOCULAR LENS C&C Vision (Aliso Viejo, CA) developed this lens, which is currently under investigation. This IOL focuses for distance when the patient fixates on distant objects and for near when the patient attempts to read by anterior displacement of the vitreous, which forces the lens optic more anterior thus creating a myopic refractive status for the eye and improving near visual function. The lens optic can move with vitreous pressure because of the optic’s flexible arms.
LENS CALCULATION FORMULAS The length of the eye as measured by A-scan determines which formula you should use to calculate the parameters of the lens.
- short eyes
- Holladay II formula
- Hoffer-Q formula
- Holladay II formula
- average eyes
- Holladay I formula
- long eyes
- SRK/T formula
SURGICAL CONSIDERATIONS
Contraindications
- all amblyopia or monocularities
- untreated peripheral retinal lattice degeneration or holes and tears or other inner retinal pathology (increases risk for retinal detachment)
- unreasonable patient expectations
- unwillingness to lose residual crystalline lens accommodation
- expectations of perfect near and distance vision
- unwillingness to lose residual crystalline lens accommodation
Patient Preparation
- Dilate pupil with 1% cyclopentalate and 2.5% phenylephrine 30 min before the procedure.
- Administer peribulbar block or topical anesthesia.
- Prepare skin and lid and draping in sterile fashion.
Standard Equipment
- keratome
- 0.12 forceps
- capsulorrhexis needle
- hydrodissection cannula
- viscoelastic substance
- lens manipulator or chopper
- phacoemulsification machine
Methods
- Create the clear corneal or scleral tunnel wound.
- Perform continuous curvilinear capsulorrhexis under viscoelastic substance control.
- Hydrodissect the lens material.
- Remove the lens using phacoaspiration, phaco cracking, or chopping (depending on the density of the lens material).
- Remove the cortex with irrigation or aspiration.
- Fill the anterior chamber and capsular bag with viscoelastic substance to protect the endothelium and intraocular structures.
- Insert and orient the implant into the capsular bag.
- Remove the viscoelastic substance with irrigation or aspiration.
- Pressurize the globe and check for wound leaks.
- Instill antibiotic and a steroid drop or ointment into the conjunctival fornix.
- Protect the eye with eyeglasses or a shield to prevent inadvertent trauma.
Alternative Treatments
- glasses or contact lenses (soft or rigid)
- excimer laser procedures [photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK); see Chapters 9 and 11]
- laser thermal keratoplasty (for low hyperopes; see Chapter 10)
- phakic IOL insertion (high myopia and hyperopia; see Chapters 14 and 16)
POSTOPERATIVE CONSIDERATIONS
Results
- Expect at least 95% of eyes to be within ±0.5 D of targeted refraction.
- There is usually virtually no induced surgical astigmatism.
- Two to 4% of patient may want to have additional enhancement surgery for residual refractive error.
Postoperative Care
- topical antibiotic (4 times a day for 1 week)
- topical corticosteroid (tapered over 4 weeks)
- ocular shield for 1 week while sleeping
- follow-up visits (at 1 day, 1 week, 1 month, 4 months, and 1 year after surgery)
- Check uncorrected distance vision.
- Check near BCVA distance and near vision with manifest refraction.
- Check IOP.
- Check lens position.
- Assess anterior segment cell and flare.
- Assess vitreous humor and posterior pole.
- Check uncorrected distance vision.
Complications and Management
- poor refractive outcome (enhancement possible)
- lack of tolerance for monovision or multifocal vision (prepare for enhancement)
- retinal detachment
- 1 to 6% annual rate after extracapsular cataract extraction
- 0.7% annual rate with no surgical intervention for high myopes (> 10 D)
- High hyperopes have a much lower rate because of the different peripheral vitreoretinal interactions in short eyes.
- 1 to 6% annual rate after extracapsular cataract extraction
- endophthalmitis
- This complication occurs in less than 0.1% of cataract surgery patients.
- Promptly tap anterior chamber or vitreous humor for culture.
- Promptly administer intravitreal broad-spectrum antibiotic coverage for gram negative and gram positive organisms.
- Adjust the antimicrobial regimen as soon as speciation and sensitivities are complete.
- This complication occurs in less than 0.1% of cataract surgery patients.
- expulsive choroidal hemorrhage
- Ensure that the wound is water tight to prevent extrusion of intraocular contents.
- Attempt scleral cut downs for choroidal drainage.
- Ensure that the wound is water tight to prevent extrusion of intraocular contents.
- retrobulbar hemorrhage with retrobulbar anesthesia
- If extensive, postpone the procedure to allow clearance of hemorrhage.
- Be alert to increased risk for complications from inappropriately high posterior vitreous pressure particularly in high hyperopes with small eyes.
- If extensive, postpone the procedure to allow clearance of hemorrhage.
- torn posterior capsule
- If vitreous presents, select and place the acrylic or PMMA IOL in the sulcus after reducing the IOL power 0.5-1.0 D if safe to do so.
- posterior capsule opacification
- endothelial damage or decompensation
- Use viscoelastic substances and a gentle surgical technique to protect the endothelium.
- If mild damage occurs, instill 5% hypertonic drops or ointment.
- Administer topical corticosteroid drops early in the postoperative period to help minimize insult.
- If chronic damage or decompensation leads to bullous keratopathy, penetrating keratoplasty may be necessary to restore the corneal clarity.
- Use viscoelastic substances and a gentle surgical technique to protect the endothelium.
- wound dehiscence
- Ensure proper wound construction.
- Confirm a tight water seal at the end of the procedure.
- Ensure proper wound construction.
- residual refractive error
- Properly understand lens formulas and how to use them.
- Have experience in dealing with a particular lens and in treating short and long eyes.
- Manage with contacts or spectacles, corneal refractive surgery, or IOL implant exchange.
- Properly understand lens formulas and how to use them.
Enhancements and Secondary Procedures
- corneal refractive surgery (for residual refractive error)
- incisional keratotomy
- radial keratotomy
- astigmatic keratotomy
- limbal relaxing incisions [often in conjunction with clear lens replacement (CLR) or cataract surgery]
- laser refractive procedures
- PRK
- LASIK [preferred method after refractive lensectomy (RL) or phakic IOL insertion]
- laser thermokeratoplasty
- an intracorneal ring (Intacs; KeraVision, Fremont, CA)
Clear Lens Extraction Plus Laser In Situ Keratomilieusis
This combined technique, also known as bioptics, was introduced by Dr. Roberto Zaldivar of Argentina for use with phakic IOLs (Figs. 13-1 and Figs. 13-2).
Advantages
- fully corrects spherical error with CLR
- fully corrects any residual spherical error or astigmatism with LASIK
- preserves high visual quality
- keeps risk for loss of BCVA minimal for even extreme corrections
Disadvantages
- need for two procedures at least 1 month apart
- risk for complications with both procedures
- potential IOL movement when suction applied during LASIK keratectomy
- expensive technology required
Figure 13-2 The two incisions are visible in the right eye. The more linear, vertical 3.2-mm incision on the left is from the refractive lensectomy (RL). The more central, round incision on the right is from the LASIK keratectomy edge.
Suggested Readings
Allen HF, Bangiaracine AB. Bacterial endophthalmitis after cataract extraction. Arch Ophthalmol. 1974;91:3-7.
Christy NE, Lall P. A randomized controlled comparison of anterior and posterior periocular injection of antibiotic in the prevention of postoperative endophthalmitis. Ophthalmic Surg. 1986;17:715-718.
Doane JF, Nordan LT, Baker RN, Slade SG. Basic tenets of lamellar refractive surgery. Ocul Surg News. 1996;Jul 1:31.
Goldberg MF. Clear lens extraction for axial myopia: an appraisal. Ophthalmology. 1987;94: 571-582.
Lindstrom RL. Retinal detachment in axial myopia. Dev Ophthalmol. 1987;14:37-41.
Miller KM, Glasgow BJ. Bacterial endophthalmitis after sutureless cataract extraction. Arch Ophthalmol. 1993;111:377-379.
Praeger DL. Five years’ follow-up in the surgical management of cataracts in high myopia treated with the Kelman phacoemulsification technique. Ophthalmology. 1979;86: 2024-2033.
Werblin TP. Clear lens/cataract extraction for refractive purposes. In: Elander R, Rich LF, Robin JB, eds. Principles and Practice of Refractive Surgery. Philadelphia: WB Saunders; 1997: 449-458.
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