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Identify preoperative risk factors to prevent keratectasia

Treatment for the condition includes both surgical and nonsurgical options.

by William J. Tullo, OD, FAAO

This course is jointly sponsored by PCON, The State University of New York State College of Optometry and Vindico Medical Education. It is COPE-approved for 2 continuing education credits.

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The most devastating and insidious postoperative complication of corneal refractive surgery is keratectasia. Keratectasia, keratoectasia, iatrogenic keratectasia, post-LASIK ectasia and progressive post-LASIK ectasia are all terms used in the literature to describe a progressive thinning of the cornea after corneal refractive surgery.

First described in the literature in 1980, Barraquer detailed a series of patients who developed a keratoconus-like condition after myopic keratomileusis. In 1998 Seiler first described ectasia after LASIK. The reported incidence of ectasia after LASIK surgery is between 1:2000 and 1:10,000.

Keratectasia is characterized by postoperative development of astigmatism or myopia that progressively becomes irregular, resulting in the loss of best corrected visual acuity. Steepening of the cornea can be found on keratometric and topographic analysis. Thinning of the central or paracentral cornea, most often inferotemporal, may also be found.

The mean time to onset after surgery is 16.3 months, ranging from 1 to 45 months. Incidence of keratectasia after PRK is uncertain but is probably much less common than after LASIK surgery. It is now clear that keratectasia can occur after any type of corneal refractive surgery, including myopic keratomileusis, anterior lamellar keratoplasty (ALK), radial keratotomy, PRK and LASIK (both myopic and hyperopic).

Etiology: Two theories

There are two basic theories why patients develop ectasia after corneal refractive surgery. The first theory states that certain patients have a genetically different type of collagen composition of their cornea. This variant composition predisposes patients to progressive corneal thinning. Most experts believe some external factors such as eye rubbing, gas-permeable contact lens wear and corneal refractive surgery may trigger the process of thinning. The genetic theory of keratectasia is supported by a case report by Wang that describes a patient who developed bilateral keratectasia after unilateral LASIK surgery.

While no single gene has been identified as responsible for keratectasia, a positive family history of keratoconus is a significant risk factor for patients seeking corneal refractive surgery. Although much research is ongoing, unfortunately, we do not yet have a genetic test to identify patients predisposed to corneal ectasia. Therefore, identifying the earliest (subclinical) forms of ectasia is the real challenge for the practitioner involved in screening patients for refractive surgery.

A second theory suggests that corneal ectasia results from the compromise of basic corneal biomechanics. Insult to collagen corneal fibrils via surgery, trauma, GP contact lens wear or eye rubbing cause the corneal matrix to lose structural integrity.

The cornea does not exhibit uniform biomechanical strength. The collagen fibrils of the anterior lamellae are smaller (30 µm to 50 µm) and more densely packed and interweave. In contrast, the posterior lamellae are larger and more loosely packed and do not interweave.

This lamellae arrangement allows for the cornea to be divided into strong and weak zones, both anterior-posterior and peripheral-central. Therefore, if excessive tissue is damaged or removed, the cornea would no longer withstand the force of the IOP. This, in combination with possible variations in IOP, may be responsible for postrefractive surgery ectasia.

Unknown variable corneal biomechanical and wound healing properties undermine the safety of corneal refractive surgery. This also explains why there are reports of patients developing keratectasia with no known risk factors. It is likely that a combination of the genetic and biomechanical theory is responsible for the corneal ectasia in the majority of postsurgical refractive surgery patients.

Surface lamellae vs. deep lamellae
Surface lamellae vs. deep lamellae: The collagen fibrils of the anterior lamellae are smaller, more densely packed and interwoven. The posterior lamellae are larger, more loosely packed and not interwoven.

Strong vs. weak cornea
Strong vs. weak cornea: The lamellae arrangement allows for the cornea to be divided into strong and weak zones, both anterior-posterior and peripheral-central.

Images: Journal of Cataract and Refractive Surgery, January 2005

Preoperative risk factors

To prevent ectasia after corneal refractive surgery we must first attempt to identify any preoperative risk factors prospective patients may exhibit. It is evident that all forms of identified ectasia including keratoconus, pellucid marginal degeneration (PMD) and keratoglobus are risk factors for progressive ectasia, and such patients generally should be refused traditional corneal refractive surgery. These conditions are often easy to identify preoperatively with normal screening techniques.

The challenge we face is identifying the keratoconus suspects or patients with forme-fruste keratoconus (FFK) and patients who are genetically predisposed to developing corneal ectasia. With FFK, the patient exhibits abnormal topography with the absence of any other clinical signs of ectasia. FFK is a topographic diagnosis and thought to represent the earliest form of corneal ectasia along a proposed spectrum of ectatic disorders.

In an attempt to limit the risk of keratectasia, the Food and Drug Administration has published a guideline recommending that a minimum of 250 µm be maintained in the residual stromal bed (RSB). Despite these recommendations, many cases of keratectasia have been confirmed with RSB greater than 300 µm and many cases with RSB below 200 µm and no signs of keratectasia. It has become clear that a RSB thickness of 250 µm should not be thought of as a “magic” safety guide for preventing ectasia.

In addition to RSB, other studies have suggested risks of keratectasia, including FFK, corneal thickness, high myopia and young age. Binder recently retrospectively analyzed a cohort of 9,600 LASIK patients and found that individual preoperative and operative factors did not in and of themselves increase the risk of keratectasia, suggesting that other possible unknown confounding factors contribute to confusion in risk analysis.

A more recent retrospective comparative and case-control study by Randleman recommends the development of a grade point scoring system in an attempt to stratify the individual risk for each patient screened for refractive surgery. He ranked the possible risk factors for ectasia in the following order of importance, 1: abnormal preoperative topography (FFK), 2: low RSB thickness, 3: young age, 4: low preoperative corneal thickness and 5: high myopia, assigning each a point value.

Cumulative points place patients in relative risk categories of low, moderate and high. Future validation of such a system would provide a valuable uniform approach to screening patients for corneal refractive surgery.

Visante OCT of Intralase flap
Visante OCT of Intralase flap: The use of femtosecond lasers for LASIK flap creation may reduce the incidence of residual stromal bed surprises.

Image: Tullo WJ

Another common finding in a chart review of patients who experienced postoperative LASIK ectasia is multiple enhancements. This fact suggests that our current methods of calculating RSB by subtraction (preoperative corneal pachymetry – ablation depth – flap thickness = RSB) may be less accurate than previously assumed. It is now clear that mechanical microkeratomes can produce flaps much thicker than the label depth plate. Standard deviations of more than 30 µm have been reported; in fact, one case report by Spadea described that a planned 120-micron flap was really 260 µm. This, combined with errors in preoperative corneal pachymetry (the thinnest point is often not central) may lead to gross over-estimation of RSB thickness.

To reduce these errors in RSB estimation, I would recommend the measurement of intraoperative stromal bed pachymetry in all primary cases when the calculated RSB is less than 300 µm and in all cases of flap lift LASIK enhancement to prevent accidental removal of excessive stromal bed tissue. In addition, extra attention should be paid to topography analysis in all proposed enhancements. The use of difference maps (preoperative topography – postoperative topography) and elevation topography have been useful in identifying patients at risk.

Future studies with ultra high frequency ultrasound measurements may help better estimate flap thickness and residual stromal beds more accurately. The current trend toward using femtosecond lasers for LASIK flap creation will probably reduce these surprises, with standard deviations of 5 µm to 10 µm.

Keratoconus as a risk factor

Keratoconus is a naturally occurring (approximately 1:2000) corneal disorder that exhibits a noninflammatory bilateral asymmetric progressive thinning of unknown etiology. Keratoconus is associated with atopia, asthma, IQ greater than 130, Down’s syndrome, Leber’s congenital amaurosis, connective tissue disorders, mitral valve prolapse, eye rubbing and GP contact lens wear. The onset is usually in the first or second decade of life.

Although no gender preference is found, women who develop keratoconus tend to develop it later in life. In rare cases, progressive ectasia may begin later in life, and the progression may stop at any time.

Although the exact pathophysiological disease process is not understood, abnormalities at many levels in the cornea and keratoconic cornea are apparent. In the past several years a great deal of research has begun to shed light on the pathogenesis of corneal ectasia.

Ku described decreased anterior stromal keratocyte density in keratoconus proportional to severity of disease (decreased corneal thickness and steeper keratometry values). Keratocyte apoptosis results from cytokine activity secondary to increased protease activity. Various triggers for the process are proposed.

Trauma (eye rubbing), surgery and inflammation cause upregulation of interleukin-1-alpha, resulting in insufficient oxidative defense (SOD3 synthesis) in keratoconic corneas, according to Olofsson. This leads to a relative loss in collagen cross-linking and inter- and intralamellar slippage, causing corneal thinning and protrusion. This cell mediated theory of keratoconus is further supported by the fact recurrence of keratoconus is seen in eyes after penetrating keratoplasty.

Many of the histological findings in keratoconus are also found in postrefractive surgery patients with keratectasia. Maguen found an abnormal epithelial basement membrane structure with increased proteinase activity (MMP-3 and MMP-10), suggesting ongoing epithelial basement membrane lysis and remodeling.

Lema found increased levels of interleukin-6, TNF-alpha and MMP-9 in the tear film of patients with keratoconus. This increase in proteinase activity and presence of inflammatory molecules puts into question the long held theory that keratoconus and keratectasia are noninflammatory processes.

GP contact lens warpage, serial topography
GP contact lens warpage, serial topography: This condition, which is included in the differential diagnosis for keratectasia, will tend to improve with the discontinuance of contact lens wear.

Image: Tullo WJ

Signs, symptoms of keratoconus

Symptoms of keratoconus include progressive blurred vision (not correctable with spectacles), monocular diplopia/polyopia (shadows), photophobia, glare, poor contrast, blinking and eye rubbing. Clinical signs of keratoconus include:

Differential diagnosis includes contact lens corneal warpage, due to soft or hard contact lenses. It is most commonly seen in patients who wear their lenses overnight. This diagnosis is made via serial topography. Contact lens related warpage will tend to improve with the discontinuance of the contact lenses. Pathologic ectasia will stay the same or worsen over time.

I recommend special attention be paid to all refractive surgery candidates who wear contact lenses and have topographic irregularities. Performing serial topography until stability is proven is essential for the safety of the patient. If any question remains regarding the normalcy of the topography, LASIK should be avoided, and repeating the topographic studies annually is a safe precaution, particularly in younger patients.

PMD is thought to be a variant of keratoconus characterized by a bilateral asymmetric focal thinning of the corneal stroma 1 mm to 2 mm above the inferior limbus between 5 and 7 o’clock with no evidence of scarring, vascularization or lipid infiltration. This progressive ectasia results in the development of against-the-rule astigmatism (sometimes more than –10 D) with minus cylinder axis 90. Rare cases may lead to corneal hydrops.

PMD often shows normal central pachymetry because the ectasia is restricted to the inferior limbal area. Early PMD will show against-the-rule astigmatism with mild topographic “crossover” and skewed radial axis. More advanced PMD shows the classic “kissing doves” or “crab claw” topography with superior flattening and a small island of inferior central flattening.

Corneal topography crucial in diagnosis

Pellucid marginal degeneration
Pellucid marginal degeneration: PMD often shows normal central pachymetry because the ectasia is restricted to the inferior limbal area.

Placido disc topography
Placido disc topography: This is a typical axial forme fruste keratoconus map.

Topography shape classification
Topography shape classification: This figure shows the range of possible topographical shapes.

Corneal topography is probably the most important factor in the diagnosis of corneal ectasia, but topography alone is not sufficient to make a clinical diagnosis. The physician must use all patient information available, including patient history, retinoscopy, manifest refraction with BCVA, ultrasound pachymetry, wavefront aberrometry and a full understanding of all associated risk factors to clinically diagnose keratectasia.

Two basic types of corneal topography are available today. The most common type that optometrists use is called placido disc topography. These maps are based on changes in anterior corneal curvature (slope) and produce the characteristic axial or tangential maps. While very useful for contact lens fitting, these maps may not be sensitive enough to pick up early ectasia thought to first occur on the posterior surface of the cornea.

Most modern placido disc topographers use a variety of mathematical algorithms developed to help differentiate suspect keratoconus from normal eyes. Common corneal shape indices such as the Rabinowitz/McDonnell I/S ratio, Maeda/Klyce KCI%/KPI indices, KISA% index, shape factor (SF), corneal irregularity measurements (CIM) and mean toric keratometry (TKM) are helpful metrics in screening patients for refractive surgery. Although highly sensitive for diagnosing keratoconus, these indices are much less sensitive and specific for early keratoconus suspects, resulting in false positives and false negative findings (6% to 29% of keratoconus suspects).

Interpreting placido axial/sagittal topography

When interpreting corneal topography it is important to follow the steps outlined in the “Topography analysis” table. Decisions should be made only by considering all historical patient data, careful comparison with contralateral eyes and serial data analysis.

The “Topography shape classification” figure and “Relative distribution” table show the shapes and relative distribution of the axial map in the normal population as reported by Rabinowitz. More than 65% of screened patients fall into the normal category and are safe for LASIK or PRK surgery. This infers that almost 35% of the patients we screen for refractive surgery are either abnormal or suspicious, warranting further scrutiny. Recommendations of the Joint American Academy of Ophthalmology/International Society of Refractive Surgery/American Society for Cataract and Refractive Surgery Committee on Corneal Ectasia after LASIK included that LASIK should be avoided in patients having patterns with asymmetrical inferior steepening or asymmetric bowtie with skewed steep radial axes.

Based on the available data in the literature, I propose a risk stratification method outlined in the “Relative risk classification” table. Abnormal patients should clearly not have corneal refractive surgery.

Relative risk classification: A method for stratifying risk

Relative distribution of the axial map in the normal populationSteps to follow in topographical analysis

Patients with skewed radial axis greater than 30 degrees with symmetric bowties or asymmetric bowties and patients with significant inferior steepening with I-S ratio greater than 1.4 are clearly abnormal. This represents between 10% and 15% of screened patients. I-S ratio is a measure of topographic asymmetry, measured at points 3 mm off center as described by Rabinowitz.

The remaining 20% to 25% of suspicious topographies must be risk stratified based on serial testing and examination of all other available patient data. While many suspicious topographies are in themselves safe for PRK, all other relevant risk factors must be considered before any corneal surgery is recommended. Additionally, many patients with contact lens warpage may exhibit suspicious topographies that are not at risk for keratectasia.

In addition to serial axial topography, elevation topography can often help differentiate contact lens warpage from FFK. Ultimately, if any refractive surgery is to be performed on patients with suspicious topographies, an extensive additional informed consent should be given, including discussing the possibility of inducing keratectasia and the potential need for corneal transplantation.

Axial topography false negatives
Axial topography false negatives: The indices used in placido disc topographers are less sensitive and specific for early keratoconus, resulting in false positives and false negative findings.

Image: Tullo WJ

Elevation topography

Elevation topographers such as the Orbscan (Bausch & Lomb, Rochester, N.Y.), Pentacam (Oculus, Lynnwood, Wash.) and Gallilei (Ziemer, Wood River, Ill.) are capable of providing elevation (not curvature) float maps of the anterior and posterior corneal surface. These devices may help in the early diagnosis of corneal ectasia and help differentiate anterior corneal surface abnormalities due to contact lens warpage from corneal ectasia.

Orbscan IIz topography uses a placido disc to measure anterior cornea curvature and a scanning slit to measure 18,000 points of surface elevation directly. A typical quad map will provide anterior and posterior float, pachymetry map and axial curvature data.

The accompanying table lists Orbscan red flags for keratoconus or keratoconus suspects. Although not all red flags carry equal weight, any patient with three red flags should not be considered for corneal refractive surgery. Patients exhibiting one or two flags have a higher relative risk, and it may be safer to consider PRK.

Advantages of this type of topography include accurate description of posterior corneal surface on nonoperated eyes, anterior curvature and elevation mapping and pachymetry mapping. Disadvantages include poor posterior corneal description after LASIK surgery, technician dependence and inter-test variability.

Pentacam HR topography uses a single rotating Scheimpflug camera and a second fixed camera to obtain a 3-D model of the anterior segment including 138,000 points of elevation. For refractive surgery screening, the typical Pentacam map is similar to the Orbscan map showing full corneal pachymetry, anterior/posterior surface elevation data and anterior axial topography.

Some of the advantages of Pentacam studies include autofocus, low inter-test variability, accurate whole corneal pachymetry and anterior/posterior elevation measurements on both preoperative and postoperative corneas. Keratoconus detection graphs of corneal thickness progression from the thinnest point may help differentiate keratoconus from normal corneas.

A study by Luz has shown that keratoconus corneas have a faster rate of progression to thinner values as compared to normal corneas. This may be an indirect index of corneal biomechanical stability. Current limitations include lack of modern keratoconus detection algorithms (current algorithms are based on curvature data) and no validated data set.

The newest elevation topography technology, the Gallilei, uses dual rotating Scheimpflug cameras to reduce artifacts due to decentration and advanced keratoconus detection methods to maximize both sensitivity and specificity of patient screening. Similar to the Pentacam, the Gallilei can produce accurate reproducible elevation mapping of both the anterior and posterior corneal surface along with full corneal pachymetry mapping.

Orbscan red flags for keratoconus or keratoconus suspects

Corneal hysteresis and keratoconus

Corneal hysteresis is a biomechanical property of the cornea that can be measured by a commercially available device called the Ocular Response Analyzer (Reichert, Depew, N.Y.). This devise applanates the cornea with a puff of air and measures IOP, corneal hysteresis (CH) and corneal resistance factor (CRF).

Although Ortiz found that both CH and CRF are reduced in patients with keratoconus, the current device does not appear to be sensitive and specific enough to differentiate keratoconus suspects from normal eyes. The hope is that future research in the area of corneal biomechanics (corneal elasticity and viscosity) will produce a device that can identify early corneal ectasia and corneas at risk before changes apparent on topographic analysis.

In summary, the physician screening patients for refractive surgery must use all the diagnostic tools at his or her disposal to minimize the chance of postoperative keratectasia. Patient history, refraction with BCVA, retinoscopy, slit-lamp examination, corneal topography, pachymetry and wavefront aberrometry are all important diagnostic tests necessary to properly screen patients for potential ectatic conditions before recommending refractive surgery.

Typical Orbscan map post-LASIK ectasia
Typical Orbscan map post-LASIK ectasia: A typical quad map will provide anterior float, posterior float, pachymetry map and axial curvature data.

Image: Tullo WJ

Elevation topogrophy identifies keratoconus suspect
Elevation topogrophy identifies keratoconus suspect: In this patient with an asymmetric bowtie, the Pentacam shows abnormal values for the anterior and posterior apices and displacement inferotemporally of the apices and the thinnest point on the pachymetry map. This patient can be clearly identified as a keratoconus suspect. The excellent reproducibility of the Pentacam facilitates comparison with follow-up studies.

Image: Tullo WJ

Post-LASIK ectasia corneal thickness progression
Post-LASIK ectasia corneal thickness progression: Some of the advantages of Pentacam studies include autofocus, low inter-test variability, accurate whole corneal pachymetry and anterior/posterior elevation measurements on both preoperative and postoperative corneas. Keratoconus detection graphs of corneal thickness progression from the thinnest point may help differentiate keratoconus from normal corneas.

Image: Tullo WJ

False-positive
False-positive: Asymmetry on the curvature map as seen is suspicious for forme fruste keratoconus, but the elevation data shows a normal anterior and posterior surface and pachymetry map. This is a normal cornea with a displaced anterior apex and a false positive on axial placido mapping.

Image: Speaker M

Nonsurgical management of corneal ectasia

The first options to consider for all patients with corneal ectasia after refractive surgery should be nonsurgical, beginning with pharmacologic reduction in IOP. Studies by Hiatt have demonstrated improvements in UCVA, BCVA, manifest refractions and topographic studies after IOP is reduced with topical glaucoma medications.

If reducing IOP pharmacologically fails, the next nonsurgical treatment is spectacle and traditional soft contact lenses. Although these options may often provide good corrected vision initially, the progressive nature of this condition often leads to reduced BCVA due to irregular astigmatism.

The next form of correction is GP and specialized custom contact lenses. While GP lenses often provide good vision, they can be difficult to fit for the average practitioner and difficult to tolerate for the patient due to physical discomfort. The Collaborative Longitudinal Evaluation of Keratoconus study taught us that GP contact lens wear is a risk factor for corneal scarring, and flat fitting GP lenses should be avoided.

Other options for contact lens wear include custom soft lenses, custom GP designs, piggyback lenses (GP on top of soft), SoClear corneal-scleral lenses (formally Macrolens, C&H Contact Lens Inc.) and SynergEyes lenses (SynergEyes Inc). The SynergEyes lenses have a unique hybrid design, a GP center with a soft skirt, unlike a previous hybrid lens, the SoftPerm by CIBA Vision. Specific designs are available for both naturally occurring keratoconus (SynergEyes KC) and LASIK-induced keratectasia (SynergEyes PS).

It has been my experience with more than 250 patients that those who develop ectasia naturally (keratoconus) will often tolerate GP contact lens correction very well (more than 90% successful full-time wear). Alternatively, patients who develop ectasia after corneal surgery are much more difficult patients to fit with spectacles and contact lenses.

Even if you achieve good comfort and good vision they often resist contact lens or spectacle wear. They will remind you several times during the fitting process “the whole reason I did refractive surgery was to get rid of these glasses or contact lenses.” Their anger and disappointment over experiencing a post-surgical complication must be dealt with before you attempt to prescribe glasses or contact lenses.

According to Potter, patients who are still grieving their vision loss will resist all forms of nonsurgical intervention. If you wait until this grieving process is completed and the patient is ready for visual correction, your chances of successfully fitting them with spectacles and contact lenses increases dramatically.

Surgical management of corneal ectasia

Surgical intervention includes replacing all or part of the cornea, adding donor tissue or supportive material to the cornea and strengthening the weakened tissue. Traditional penetrating keratoplasty (PKP) uses a manual trephine to transplant 7 mm to 8 mm full thickness human donor tissue.

Donor buttons are sutured into place with interrupted and running sutures. While postoperative complications are rare, they include wound leak, secondary glaucoma, infectious keratitis, graft rejection and endophthalmitis. Despite a high success rate, long visual recovery, significant residual refractive error and often irregular astigmatism can reduce patient satisfaction.

Many surgeons feel that patients with corneal ectasia are better off having partial corneal replacement. Because most patients with corneal ectasia have normal corneal endothelium, anterior lamellar (ALK) is often a better option. ALK is less invasive as compared to PKP, because no full thickness cuts are made in the recipient cornea.

Prepared with a mechanical microkeratome, a donor disc of about 250 µm of stromal tissue is sutured and glued onto the recipient corneal stromal bed. Complications are generally less compared to PKP, and suture removal and visual recovery are faster (3 to 6 months). Unfortunately, significant astigmatism is still common, requiring further visual rehabilitation, often with GP contact lens.

PKP with femtosecond laser

A new procedure modification for full PKP is the use of the femtosecond laser to prepare the recipient and harvest donor tissue. Intralase enabled keratoplasty (IEK), approved by the FDA in July 2005, uses shaped penetrating cuts to produce a better-fitting, tighter-adhering donor button.

This method uses a femtosecond laser to remove the diseased host tissue and to harvest the donor tissue. The use of the laser allows for a complex edge designs (mushroom or zigzag) resulting in a more precise fit. The technique is easier to perform and less surgeon dependent. Less suturing (often only eight interrupted sutures) and faster suture removal (3 to 4 months) allow for rapid visual recovery. Complications common in PKP such as wound leaks and high irregular astigmatism are reportedly dramatically reduced.

Initial reports by Naranjo-Tackman described nine eyes exhibiting less postoperative astigmatism (range -0.75 D to -2.00 D, mean -1.33 D), faster visual recovery (suture removed at 3 months) and better UCVA (all nine eyes between 20/50 and 20/100 at 1-day postoperative).

Other new surgical techniques described by Tan, including femtosecond laser-assisted deep anterior lamellar, intralamellar keratoplasty (ILK) and peripheral tectonic lamellar keratoplasty (PTLK) have shown to improve and restore the structural integrity of the ectatic cornea, decrease corneal astigmatism and improve BCVA and UCVA.

Intralase-enabled keratoplasty
Intralase-enabled keratoplasty: IEK uses a femtosecond laser to remove the diseased host tissue and to harvest the donor tissue in penetrating keratoplasty.

Image: Tullo WJ

Intacs for ectasia

Intracorneal ring segments (Intacs, Addition Technology Inc.) are another option to help patients with corneal ectasia. Although originally intended for the correction of myopia in normal eyes, Intacs can be used to reduce the irregularity of the astigmatism by raising the thinned area of protrusion.

One inferior ring or two rings are inserted at the steep axis of cylinder. The channels for the rings are made with a manual trephine approximately two-thirds the depth of the peripheral cornea. A minimum of 400 µm of tissue must be present at the site of the channel.

This manual technique can be surgically challenging even for the experienced corneal surgeon. Recently the procedure of creating the channels has been simplified and automated by the use of the femtosecond laser. Colin has reported that more than 80% of patients have contact lens tolerance restored after Intacs insertion.

The primary goal of this procedure is to improve the BCVA with subsequent spectacle correction or improve tolerance of and ease of contact lens fit. While UCVA may sometimes improve, it is important to educate patients undergoing this procedure that they may not see any better with their “naked eyes” to avoid significant disappointment. This procedure is often a method to put off inevitable corneal replacement surgery.

Complications from this procedure may include anterior chamber or epithelial perforation, segment extrusion, infectious/sterile keratitis, channel haze, photophobia, glare/halo, neovascularization of incision site and adverse physical appearance.

Conductive keratoplasty for ectasia

Conductive keratoplasty (CK) uses a low energy radiofrequency current to thermally shrink corneal collagen. Although originally FDA approved for correcting low to moderate hyperopia and presbyopia, CK can be used to reduce astigmatism in eyes with keratectasia.

The surgeon will initially apply one or two spots in the flat axis on the 7 mm optic zone. If greater effect is desired, one or two additional spots are added on the 8 mm optic zone. Alio described visual improvement and normalization of topography after CK application to eyes with keratoconus. CK’s effect can be additive to the effects of Intacs corneal ring segments on corneas with keratectasia.

C3-R: Similar to PRK

C3-R is a method of collagen cross-linking of the cornea using riboflavin and ultraviolet (UV) light. Initial technique involved removal of the central 7 mm of epithelium similar to PRK surgery with subsequent topical application of riboflavin with UVA exposure for 30 minutes (equivalent to less than 1 hour at the beach).

A newer more patient friendly method by Brian Boxer-Wachler, MD, involves repeated 30-minute applications of 0.1% riboflavin every 3 minutes over intact epithelium with 0.5% tetracaine every 10 minutes to increase epithelial permeability. The combination of the vitamin B2 (riboflavin) and the UVA light causes photopolymerization, increasing the rigidity of the corneal collagen, enabling the cornea to biomechanically resist keratectasia.

While many initial studies show a halt in the progression of the ectasia, many eyes also show regression towards a more normal corneal shape. Wollensak was able to stop the progression of keratoconus in 100% of 60 eyes with 5-year follow-up. He described flattening of 2.87 D of the steep keratometry reading in 52% of eyes treated. No significant side effects have yet been reported. A possible side effect may include stromal hazing.

Although this method is not yet FDA approved, many international users are reporting remarkable initial results. Chan describe a synergistic effect of inferior Intacs segments when pre-treating keratoconic corneas with C3-R. Kanellopoulos in Athens, Greece, performs corneal cross-linking with sequential topography-guided PRK as an alternative to PK surgery. This technique has reportedly reduced his need for performing PK surgery by more than 90%.

Well controlled prospective studies are underway, and it is hoped that they will prove the safety and efficacy of this remarkable procedure.

Increased interest, awareness high

The dramatic increased interest and awareness of ectasia after refractive surgery is currently at an all-time high. Our desire to keep our patients safe and “do no harm” is the integral mindset of all physicians screening patients for refractive surgery.

Any optometrist or ophthalmologist who has had a patient develop keratectasia after refractive surgery will tell you they hope never to have to manage another patient like that again. It is often a difficult emotional experience for everyone involved. Because of the difficult nature of managing these patients, a breakdown in the doctor-patient relationship often develops, leading to a cessation of productive medical care and an increased risk of litigation for the physicians involved.

The incidence of post-refractive surgery ectasia has decreased over the past several years. The peak number of cases of keratectasia originates from surgery performed prior to 2003.

The cause of the decreased incidence of keratectasia over the past 3 to 5 years is likely due to several factors. Improved screening of refractive surgery candidates, particularly our better understanding of corneal topography and the commercial availability of elevation topography, has improved our ability to identify FFK. In addition, more precise microkeratomes (mechanical and femtosecond laser) producing thinner, less variable flaps is likely responsible for the decreasing incidence.

Better understanding of the underlying pathogenesis, corneal biomechanics and genetic predilection of corneal ectasia along with continued improvement in diagnostic screening and testing will help further reduce the incidence of keratectasia. Possible refinement and validation of a neural network using all known risk factors may someday give doctors screening patients for refractive surgery a more accurate risk assessment of ectasia development. Better treatment modalities such as collagen cross-linking and IEK promise a better future for patients currently suffering from this most unfortunate condition.

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