CORNEA AND REFRACTIVE SURGERY
From the 31st Annual UC Davis Ophthalmology Symposium, Elder Eyes: New Treatments for the Aging Eye, presented by
University of California, Davis, Health System
Terry Kim, MD, Associate Professor of Ophthalmology, Duke University School of Medicine; Director of Fellowship
Programs, and Associate Director, Corneal and External Disease Service and Refractive Surgery Service, Duke University
Eye Center, Durham, NC
Educational Objectives
| The goal of this program is to improve corneal, cataract, and refractive surgery. After hearing and assimilating this program,
the clinician will be better able to:
|
 | 1. Review the factors that affect clear corneal incisions (CCIs).
|
| 2. Discuss the advantages of smaller CCIs.
|
| 3. Demonstrate the advantages of using fibrin adhesives in cataract and pterygium surgery.
|
| 4. Describe the variety of intraocular lenses (IOLs) currently being used.
|
| 5. Recognize and practice the keys to success with IOLs.
|
Faculty Disclosure
In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and members of the planning
committee to disclose relevant financial relationships within the past 12 months that might create any personal conflicts of interest.
Any identified conflicts were resolved to ensure that this educational activity promotes quality in health care and not a
proprietary business or commercial interest. For this program, the following has been disclosed: Dr. Kim is a consultant for
Alcon, Allergan, Becton-Dickinson, ForSight Labs, Hyperbranch Medical Technology, ISTA, and SIA Healthcare Advisors.
The planning committee reported nothing to disclose.
Acknowledgements
Dr. Kim was recorded at the 31st Annual UC Davis Ophthalmology Symposium, Elder Eyes: New Treatments for the
Aging Eye, held May 16-18, 2008, in Napa, CA, and sponsored by the University of California, Davis, Health System,
Office of Continuing Education, and Department of Ophthalmology and Vision Science. The Audio-Digest Foundation
thanks Dr. Kim and the University of California, Davis, for their cooperation in the production of this program.
| ADVANCES IN SMALL-INCISION PHACOEMULSIFICATION SURGERY
|
| Introduction: 0.1% incidence of endophthalmitis after cataract surgery often quoted; published data show rate increasing; recent
European Society of Cataract and Refractive Surgeons (ESCRS) survey shows incidence 0.38%; studies available that
support and refute link between endophthalmitis and clear corneal incisions (CCIs); CCIs not perfect; McDonnell, using optical
coherence tomography (OCT), showed that incisions seal well when intraocular pressure (IOP) high; lowering IOP leads
to internal gaping of incision (possibly how organisms enter eye)
|
| Factors affecting CCIs: location—limbal; clear corneal; superior; oblique; temporal; geometry—width; chord length
(tunnel); angle; IOP; surgical—phacoemulsification (PE); delivery system; stromal hydration; in transitioning to smaller
CCIs (bimanual 1.2-1.4 mm or microaxial PE techniques requiring 2.2-2.4 mm), adjustments made for instrumentation,
fluidics, incision distortion, and surgical technique; learning curve present; smaller incisions heal faster, induce less astigmatism,
and associated with less risk for endophthalmitis; limitations of bimanual PE—inadequate infusion; overlocking
of instruments; distortion of incision; incisions typically leaked at end of case
|
| Evaluation of coaxial, microincisional coaxial, and bimanual microincisional techniques: involved 15
human cadaver eyes; categorized into 3 groups, based on incision length and simulated PE technique; no actual lens extraction
performed; 3 groups included 2.75-mm group, 2.2-mm group (both coaxial), and 1.2-mm (bimanual incision)
group; coaxial group used same 30° flared aspiration bypass system (ABS) tip with various sleeves; Microsurgical Technologies
(MST) system (sleeveless) used in third group; all PE and aspiration settings comparable; performed for 3 min;
incision gauges used to confirm width of incisions; spontaneous wound leakage and entry of India ink, when placed on
surface of eyes, found in all eyes in which bimanual PE performed, and in 1 of 10 eyes subjected to coaxial technique
(2.75-mm incision); histopathology showed that India ink infused along wound track of 1.2-mm incisions; India ink used
because it simulates size of bacteria; scanning electron microscopy (SEM) qualitatively found more trauma to Descemet’s
membrane in smaller incision, compared to 2.2-mm and 2.75-mm coaxial incisions; conclusions—wound compromise
occurs, potentially leading to secretions or microorganisms entering eye, seeding anterior chamber and vitreous,
and causing endophthalmitis; bimanual microincisional PE induced more stress to wound, but further studies warranted;
examination of incisions in human patients using anterior segment OCT showed considerable stromal hydration in standard
2.8-mm incision immediately postoperatively, with gaping of posterior aspect of incision (still present on postoperative
day 1)
|
| Appropriate incision management: square incision advantageous (seals better); routine stromal hydration; testing of
wound (pressing on opposite side of incision); low tolerance for suture placement; evaluating ideal sealant for wound protection
recommended; tips and sleeves—with 2.2-mm incision, speaker recommends mini-flared tip (speaker uses 0.9-
mm mini-flared tip with “ultra” sleeve); sleeve adds protection to wound against mechanical and thermal stress; PE
chop—speaker uses horizontal chop technique at periphery of lens; removal of epinucleus—easy and quick; speaker
performs hydrodelineation after hydrodissection; study—compared corneal wound architecture and integrity after OZil
torsional and mixed ultrasonography (US) modalities; 2 sizes of incisions (2.75 mm and 2.2 mm); 20 human cadaver eyes
( 4 groups of 5 eyes each); group 1, 2.75 mm with 100% OZil; group 2, 2.2 mm with 70% OZil; group 3, 2.2 mm with
100% OZil; group 4, 2.2 mm with mixed US; PE settings kept constant among 4 groups; analysis of all groups included
India ink, histopathology, OCT, and SEM; no difference found in spontaneous wound leakage, except for one in 2.75-mm
group; no India ink penetrated into inner wound tract in any eyes; OCT results without stromal hydration after simulated
PE similar in all groups; SEM also similar; concluded that no differences in corneal wound architecture, and integrity observed
among 4 treatment groups, as confirmed by gross, histopathologic, OCT, and SEM examination
|
| Study supporting smaller incisions: looked at various intraoperative and clinical parameters using OZil torsional
handpiece through 2.8-mm vs standard 2.75-mm incision; 32 patients underwent bilateral cataract surgery; all had symmetric
cataracts, according to slit lamp examination; right eye underwent standard 2.8-mm incision with 0.9-mm tapered 30°
beveled tip and microsleeve (100% torsional); left eye received 2.2-mm incision with 0.9-mm mini-flared 45° beveled tip;
clinical parameters included central corneal thickness on postoperative day 1, endothelial cell count at postoperative month
6, and anterior segment OCT; intraoperatively, looked at cumulative dissipated energy (CDE) and complications that occurred,
and measured use of balanced salt solution; only 2 factors statistically significant were CDE use (less in 2.2-mm eye)
and endothelial cell count at postoperative month 6 (less cell loss in 2.2-mm eye); no complications in either group; no difference
in OCT; conclusion—coaxial microincisional cataract surgery with OZil results in favorable clinical and intraoperative
characteristics
|
| INCORPORATING TISSUE ADHESIVES IN CATARACT, CORNEAL, AND REFRACTIVE SURGERY
|
| Introduction: cyanoacrylate adhesive for cataract surgery and fibrin adhesive for pterygium surgery, lamellar keratoplasty,
and laser-assisted in situ keratomileusis (LASIK) not Food and Drug Administration (FDA)-approved (all used
off-label)
|
| Disadvantages of conventional ophthalmic suture: trauma to cornea, infection, and neovascularization; requires
time and skill
|
| Cyanoacrylate adhesives: used mostly for corneal melts or perforations; typically isobutyl or n-butyl formulation;
used off-label for >20 yr; Squeez-ett pipette (dental product; manufactured by Ellman International) or tuberculosis syringe
used to get minute amount into focal perforation
|
| Postcataract surgery endophthalmitis: as shown in Endophthalmitis Vitrectomy Study, 70% of patients with bacterial
endolphthalmitis culture-positive, and >90% of organisms gram-positive (reside on lid margin of eye)
|
| Endophthalmitis with CCI: incidence 0.07% to 0.3%; ESCRS prospective study showed incidence 0.2% for proven
cases (0.4% for suspected cases); incidence of endophthalmitis 3 to 5 times higher with CCI vs scleral tunnel incisions;
ESCRS found CCI had odds ratio of 7.4 for risk of endophthalmitis
|
| Use of cyanoacrylate glue to seal cataract wounds: clinical trial using octylcyanoacrylate with parabens (Liquid
Bandage); 60% to 70% of patients experienced foreign body sensation and focal conjunctival injection localized to cyanoacrylate
glue which fell off after 1 to 2 days (fairly toxic)
|
| Pterygium surgery: adhesives increasingly being used; 2 forms of amniotic membrane used; speaker pleased with use
of fibrin-based adhesive (Tisseel) with amniotic membrane graft (Amniograft or dehydrated AmbioDry); Tisseel—2
components include fibrinogen (vapor-heated, freeze-dried) mixed with fibrinolysis-inhibitor solution (bovine source),
and thrombin (vapor-heated, freeze-dried) mixed with calcium chloride solution; placed in double-barreled syringe;
AmbioDry—dehydrated amniotic membrane; no freezing or refrigeration needed; no filter paper substrate; orientation
basement membrane side up in plastic packaging; activates and becomes “mushy” as soon as wet; works well with Tisseel
adhesive; epithelial ingrowth—increased incidence after LASIK; in severe cases, necessary to lift flap, scrape epithelium
off stromal bed and underside of flap, and replace flap; necessary to suture flap down to close gap and prevent
epithelium from going back; important to remove epithelium away from edge of flap; Tisseel for LASIK flap
complications—advantages no flap suturing or suture removal, faster operative time, and technically easy; disadvantages
discomfort and irritation, limited visualization of flap interface, setup time, and cost; because of bovine source, concern
with prion transmission
|
| Designing adhesives for ophthalmic use: 2 types; first type cross-linked with argon laser light; other type self-gelling
mechanism in which 2 components mixed; in 4.1-mm wounds, whether linear or stellate, adhesive group better at
sealing than suture controls; adhesives also used to seal 3-mm CCIs
|
| Liquid ocular bandage (OcuSeal): synthetic dendritic hydrogel with unique applicator; cross-links in 30 sec;
painted on in low-profile beam to eye; stains with fluorescein; no foreign body sensation; falls off within 24 to 48 hr;
study—determined whether small pore size of OcuSeal prevents passage of bacteria; used Dey and Engley (D/E) agar
(changes from purple to yellow in presence of acidic microbial products); at 24 hr, none of samples turned yellow; available
in United States for compassionate use only
|
| PRINCIPLES AND PEARLS FOR NEW-TECHNOLOGY INTRAOCULAR LENSES
|
| Presbyopia-correcting intraocular lenses (IOLs): Crystalens—approved by FDA; silicone lens based on flexible
hinged haptic design; moves forward and backward to help with accommodation (mechanism not clear); original
model had 4.5-mm optic that sat posteriorly in capsular bed; new model (Crystalens 5.0) has 5.0-mm optic; provides
good intermediate and distance vision, but lacking in up-close-range vision; Crystalens 5.0 goes through ≈3-mm incision
|
| Multifocal lenses: no hinged optics and no movement of lens itself; problems with glare halos, and contrast sensitivity
from optic design; 2 types, refractive multizonal design (power changes from center to periphery) and diffractive design
(2 focal points by diffraction at interference grid); Acrysof ReSTOR IOL—approved by FDA in March 2005; comes in 1-
piece and 3-piece acrylic; necessary to place lens in sulcus; refractive zone in periphery and apodized diffractive zone
(3.6 mm); +4.0 add equivalent; ReZoom Multifocal IOL—hydrophobic acrylic material; 3-piece design; utilizes Balanced
View Optics technology; better for distance and intermediate vision; currently, no head-to-head comparisons with
other models of lenses; ReSTOR Aspheric IOL—aspheric form due to its interior aspheric optic (otherwise, lens design
same as original ReSTOR lens); goal to induce negative spherical aberrations; important because most corneas induce
positive spherical aberration (balance each other out in young eye); as patient ages, lens becomes sclerotic, harder, and
starts inducing positive spherical aberration that interferes with positive spherical aberration of cornea; patient ends up
with distorted vision due to overrefraction of light rays from periphery of lens; goal of aspheric IOL to provide thinner
lens that induces negative spherical aberration (cancels positive spherical aberration of most corneas, resulting in more
focused point in retina and improved image quality); provides improved distance vision; higher percentage of patients obtain
20/20 or 20/25 vision postoperatively; near vision still good
|
| Keys to success: patient management—includes patient selection; exclusion criteria recommended (eg, hypercritical patients,
patients with unrealistic expectations, occupational night drivers); medical exclusion criteria (eg, patients with
>1.0 diopter [D] of corneal astigmatism, those with preexisting ocular pathology); avoid patients with previous refractive
surgery; inclusion criteria include patients with desire to be spectacle-free, those unhappy with monovision, and those
with realistic expectations; also hyperopic presbyopes for beginning surgeons and those with <1.0 D of corneal astigmatism;
management of expectations—determination of patient’s expectations key; Dell questionnaire useful (question 7,
which asks patient to describe personality, most important); patient education—educate patients before consultation
with, eg, brochures, videos; remember adage “undersell and overperform”; with original ReSTOR IOLs, speaker advises
patient that vision possibly limited (due to decreased contrast sensitivity and basic design of IOLs; however, this weakness
drastically improved with ReSTOR Aspheric IOL) and glare halos possible (occur in ≈5% of participants in clinical
trials); intermediate vision possibly not perfect but improves with time; bilateral procedure (due to bilateral summation)
|
| Surgical planning: schedule eyes 2 to 3 wk apart; treat dominant eye first; astigmatism goal <0.5 D; advise patient of
limitations of measurements and potential for enhancement; accurate keratometry important—speaker believes manual
keratometry readings most reliable; consider corneal topography as “tie breaker”; do not be misled by lenticular astigmatism;
accurate biometry—immersion US and optical biometry (IOL Master) performed on every patient undergoing cataract
surgery; speaker uses Holiday I formula for emmetropic, normal, and longer-sized eyes, and Hoffer Q formula for
shorter eyes; personalize A-constant; management of astigmatism—speaker prefers limbal-relaxing incision because
coupling ratio remains 1:1, and less irregular astigmatism, less axis shift, and less overcorrection seen; pick nomogram;
variability in constructing incision, angulation, incision size, and limbus diameter of eye; mark eye preoperatively; surgical
technique—round centered capsulorrhexis important, especially with ReSTOR Aspheric IOLs (larger capsulorrhexis
necessary with Crystalens); remove all viscoelastic from behind lens to avoid trapped viscoelastic that may cause myopic
shift; more meticulous cortical removal; position lens at 12- and 6 o’clock positions, with slight nasal decentration to center
on pupil; lens centered in temporal bag almost always temporal to pupil; postoperative counseling—maintain communication
with unhappy patients; test distance and near vision with both eyes together; -3.00 trial lens test (with
ReSTOR lens) allows patients to experience what they would have missed if monofocal lens placed; important to determine
reason for patient’s unhappiness; most common reason residual astigmatism; look for dry eyes, posterior capsular
opacification, and cystoid macular edema; treat potential complaints as observations; reassure patients and advise them
that time needed to heal; let patients know option available if unhappy about replacing or exchanging lenses
|
| Toric IOLs: correct astigmatism; in clinical trials, results excellent for rotational stability, reduction of absolute residual refractive
cylinder, improved uncorrected vision, and percentage of patients spectacle-free; easy procedure that requires only
minor variation from standard procedure; 3 steps include IOL calculation (Toric IOL calculator), marking of eye preoperatively,
and alignment of IOL; to determine lens power, utilize AcrySof Toric IOL calculator (available online); place reference
marks (at 3- and 9 o’clock positions) while patient sitting up; do not reverse direction of lens for rotation (instead, rotate
lens in clockwise direction almost 180° [leave short ≈20°])
|
Suggested Reading
Ang LP et al: Autologous cultivated conjunctival transplantation for pterygium surgery. Am J Ophthalmol 139:611,
2005; Bloom JN et al: A light-activated surgical adhesive technique for sutureless ophthalmic surgery. Arch Ophthalmol
121:1591, 2003; Cooper BA et al: Case-control study of endophthalmitis after cataract surgery comparing scleral tunnel
and clear corneal wounds. Am J Ophthalmol 136:300, 2003; Faulkner W: Inflow of ocular surface fluid into the anterior
chamber after phacoemulsification through sutureless corneal cataract wounds. Am J Ophthalmol 141:781; author reply
781, 2006; Küçükerdönmez C et al: Vascularization is more delayed in amniotic membrane graft than conjunctival autograft
after pterygium excision. Am J Ophthalmol 143:245, 2007; Epub 2006 Nov 27.Olson RJ et al: New intraocular
lens technology. Am J Ophthalmol 140:709, 2005; Parmar P et al: Anterior chamber contamination during phacoemulsification
and manual small-incision cataract surgery. Am J Ophthalmol 141:1160, 2006; Pepose JS et al: Visual performance
of patients with bilateral vs combination Crystalens, ReZoom, and ReSTOR intraocular lens implants. Am J
Ophthalmol 144:347, 2007; Ritterband DC et al: Laboratory model of tissue adhesive (2-octyl cyanoacrylate) in sealing
clear corneal cataract wounds. Am J Ophthalmol 140:1039, 2005; Taban M et al: Acute endophthalmitis following
cataract surgery: a systematic review of the literature. Arch Ophthalmol 123:613, 2005; Taban M et al: Ingress of India
ink into the anterior chamber through sutureless clear corneal cataract wounds. Arch Ophthalmol 123:643, 2005; Wormald
RP: Phacoemulsification vs small-incision manual cataract surgery: an expert trial. Am J Ophthalmol 143:143, 2007;
Yeh DL et al: Treatment of traumatic LASIK flap dislocation and epithelial ingrowth with fibrin glue. Am J Ophthalmol
141:960, 2006.
|
