Corneal and Refractive Surgery Complications
J. Bradley Randleman, MD; Marcony R. Santhiago, MD, PhD; and William J. Dupps, MD, PhD
A variety of complications are possible after corneal and refractive surgery. Some complications have unique findings on imaging, while others do not. Complications may arise from ablation-related issues, LASIK flap creation and/or positioning issues, LASIK or small incision lenticule extraction (SMILE) interface complications, irregular healing responses following surface ablation, issues arising from incisional refractive surgery, segment extrusion or scarring after intracorneal ring segments (ICRS) placement, and issues arising after phakic intraocular lens (PIOL) implantation. There are also a multitude of complications that can arise after keratoplasty where advanced corneal imaging can prove useful in determining the etiology of the complication and directing appropriate management.
Refractive surgery is exceptionally safe, and vision-threatening complications occur rarely. The images shown in this chapter are, therefore, particularly relevant for practitioners who manage refractive surgery patients postoperatively because the rarity of complication occurrence means that most individuals will see very few of these complications arise in their own practice but must be prepared to diagnose, treat, and/or refer patients appropriately when they do present. Many of these complications have overlapping findings that create further diagnostic and treatment challenges.
Ablation issues can take on multiple forms, including technically correct ablations that nonetheless may reduce optical quality, irregular ablations, decentered ablations, central islands, and ablation errors, where incorrect programming caused incorrect ablation patterns to be employed. Ablation complications that result in irregular astigmatism, including some irregular or decentered ablations and most central islands, are particularly problematic as they typically reduce best corrected visual acuity (BCVA). Central island formation is fortunately an uncommon occurrence with modern excimer lasers. Ablation errors may be reversible depending on the extremity of the induced refractive error.
Basic Ablation Issues
A patient presented complaining of reduced vision quality and night vision issues following high myopic ablation with a conventional ablation profile.
Figure 8-1-1. Scheimpflug composite image. Axial anterior curvature (upper left) displays central flattening in a region just at the edge of the pupil diameter as measured by the imaging device (broken white circle). Tangential curvature (upper right) demonstrates the abruptness of the optical zone change in this treatment, with minimal if any transition zone treatment. Pachymetry map (lower left) demonstrates the focal ablation that was performed, with abruptly reduced central thickness within the pupillary zone. The Zernike image (lower right) shows significant higher-order aberrations, particularly spherical aberration, in this cornea.
A patient presented complaining of reduced visual quality following photorefractive keratectomy (PRK) for high hyperopia (+6 D). The patient lost 2 lines of BCVA in both the right and left eye postoperatively.
Figure 8-1-2. Placido composite image of pre- (upper) and postoperative (lower) topographies. Preoperative topographies are unremarkable. Postoperative topographies are consistent with a high hyperopic ablation, with significant central steepening in both eyes. Central K is more than 50 D in both eyes. Treatment zones appear relatively well centered in both eyes, with possible mild superior decentration in the right eye. Functional optical zones appear small in both eyes (4-mm diameter), which is common for high hyperopic treatments.
A patient who presented for cataract evaluation complained of decreased visual quality for many years following LASIK for high hyperopia.
Figure 8-1-3. Scanning slit imaging from the (A) right and (B) left eyes. Anterior curvature (lower left) is notable for maximal steepening inferior to the center, which appears as a functionally decentered optical zone in both eyes. Corneal thickness (lower right) is significantly thin centrally, which indicates that thickness was low preoperatively, because hyperopic ablations remove tissue peripherally rather than centrally.
Figure 8-1-3. (C) Scheimpflug comparative image of the same patient. Anterior curvature (upper) and corneal thickness (lower) are shown. Both curvature and thickness appear relatively analogous to those shown in scanning slit imaging, but the optical zones appear better centered in Scheimpflug imaging. Central K is more than 50 D in both eyes. Figure 8-1-3. Scheimpflug composite images of anterior curvature in different scales for the (D) right and (E) left eyes from the same patient. Scales shown are [A] Atlas, [B] Oculus, [C] American, and [D] TMS. Note the different appearance of the patterns in each scale, all of which are set in 0. 5 D color scales. Case note: In this case the Atlas scale loses some sensitivity for local curvature changes due to the central curvature exceeding the basic scale, making all central curvature appear relative uniform in red (> 50), when in fact there is central irregularity that is better demonstrated in other scale maps (B to D). Nevertheless, the optical zone appears better centered in Scheimpflug imaging as compared with scanning slit imaging.
Irregular Ablations
A patient complained of reduced visual quality in the right eye in the first weeks after LASIK.
Figure 8-1-4. (A) Diagram of peripheral laser ablation that impacted both the stromal bed surface (as anticipated) and the flap undersurface (not anticipated). The arrow shows the location of the peripheral ablation spots hitting both surfaces. (B) Diagram showing the physical result of the double ablation occurring on both the stromal surface and flap undersurface. The result is an additional unintended focal tissue ablation. (C) Placido image from the early postoperative period in the patient’s right eye, with flap undersurface ablation as diagramed in the previous images. There is significant irregular astigmatism, with central steepening in a truncated bowtie pattern adjacent to a peripheral area of excessive flattening (arrow) corresponding to the area of excessive ablation.
A patient complained of poor visual quality with or without correction after undergoing LASIK for high hyperopia (≈4 D) followed by multiple PRK retreatments on the flap surface.
Figure 8-1-5. (A) Scanning slit imaging of the right eye. Anterior curvature is notable for central steepening and significant central irregularity, with some regions being steeper than 50 D. Pachymetry mapping looks abnormal, with significant central thinning and maximal apparent thinning superiorly (artifactual). There are significant focal elevations on anterior and posterior surface maps. (B) Scheimpflug refractive display of the same eye. Anterior curvature appears steep in a pattern somewhat analogous to that seen in scanning slit imaging, but the central irregularity is masked by the scale utilized. Corneal thickness maps show maximal corneal thinning in the periphery in a ring around the center but does not show any focal location of thinning like that shown in scanning slit imaging. Anterior elevation map shows central focal elevation corresponding to the steepest curvature. There is no focal elevation noted on the posterior surface.
Figure 8-1-5. (C) Spectral domain optical coherence tomography (SD-OCT) cross-sectional imaging of the same eye. Total thickness is not displayed in this image, but the cornea does not appear to be thinned to the level shown in scanning slit imaging. There is central superficial scarring with epithelial hypertrophy (central white arrows). The flap interface is visible in the far periphery (single white arrow) but not visible in the mid-periphery because the subsequent surface ablations ablated full thickness through the LASIK flap. (D) Scanning slit imaging of the same eye after LASIK flap excision. Anterior curvature is now significantly more regular, displaying an asymmetric bowtie with-the-rule pattern. Corneal thickness displays artifactual thinning from the peripheral haze, and the posterior surface map is similarly altered artifactually. Anterior elevation is significantly reduced as compared to Figure 8-1-5A. Figure 8-1-5. (E) Scheimpflug refractive display of the same eye after LASIK flap excision. Anterior curvature (upper left) appears analogous to scanning slit imaging with an asymmetric bowtie pattern. Pachymetry map displays a thin but more regular thickness than scanning slit imaging. Maximal anterior elevation has reduced from 38 μm (Figure 8-1-5B) to 19 μm. (F) Scheimpflug difference maps of anterior curvature before (middle) and after (left) flap excision. There has been almost 10 D reduction in focal steepening centrally. Case note: Scanning slit imaging is inherently susceptible to generating pachymetry artifacts in corneas with any significant haze or scarring. As shown in this case, Scheimpflug imaging performs better for those eyes for pachymetry and posterior surface measurements. Anterior curvature is usually relatively accurately represented by the Placido imaging utilized in scanning slit imaging, and anterior elevation is also less sensitive to scarring artifact. A patient presented complaining of reduced visual quality in the right eye. The patient underwent myopic LASIK many years ago and had a PRK retreatment with subsequent conductive keratoplasty (CK) in the far periphery performed within the past year prior to presentation. Figure 8-1-6. (A) Scheimpflug imaging of the right eye. Anterior curvature shows focal flattening displaced nasally outside the pupillary border (dashed line). The focal steep peripheral spots in the far periphery indicate the locations of CK spots. Corneal thickness maps show well-centered corneal thinning consistent with a myopic ablation. Anterior elevation shows a relatively well-centered focal depression consistent with myopic ablation, while there is no notable pattern in posterior elevation. (B) SD-OCT imaging of the same eye. Total thickness is analogous to Scheimpflug imaging and the thinnest point is well centered. Epithelial mapping shows significant epithelial hyperplasia temporally. Figure 8-1-6. (C) Scheimpflug imaging of the same eye after superficial keratectomy. Anterior curvature is more normalized centrally within the pupillary zone. Corneal thickness is minimally different than before treatment. Anterior and posterior elevations are more centrally located in both maps compared to pretreatment imaging. (D) SD-OCT imaging of the same eye after superficial keratectomy. Epithelial mapping shows a more regularized epithelial thickness across the central 6 mm. Figure 8-1-6. (E) Scheimpflug difference mapping showing anterior curvature before (middle) and after (left) superficial keratectomy. There is flattening up to 3 D temporally. (F) Composite image showing Scheimpflug curvature (left) and SD-OCT epithelial thickness before (upper right) and after (lower right) superficial keratectomy. The change in curvature clearly directly corresponds to epithelial remodeling after superficial keratectomy. Case note: This case is a great example of how regional epithelial thickness impacts corneal curvature. Normalizing epithelial thickness without further stromal ablation resulted in relatively normalized anterior curvature and improved visual acuity (from 20/30 BCVA to 20/20 uncorrected visual acuity [UCVA]).
Decentered Ablations
Figure 8-1-7. Scheimpflug imaging of the right eye from a patient who underwent myopic LASIK. Anterior curvature shows an area of maximal flattening displaced inferotemporally with compensatory steepening superonasally. The curvature changes are not readily apparent because the scale used is 1.5 D. Corneal thickness shows the thinnest point also displaced inferotemporally, coincident with flattest curvature. The anterior elevation depression from myopic ablation is also displaced inferiorly.
A patient who underwent myopic LASIK complained of ghosting and monocular diplopia in the right eye.
Figure 8-1-8. (A) Scanning slit imaging from the patient’s right eye prior to LASIK. Anterior curvature is notable for a mild asymmetric bowtie pattern in with-the-rule orientation. Corneal thickness shows central pachymetry of 600 μm centrally.
Figure 8-1-8. (B) Scanning slit imaging of the same eye after myopic LASIK. The area of maximal flattening on anterior curvature is significantly displaced nasally. Anterior elevation has maximal depression decentered nasally, coincident with flattest curvature. Pachymetry map shows the thinnest point displaced nasally. Peripheral thickness values are also reduced nasally as compared to preoperative values. (C) Placido imaging of the same eye showing maximal flattening displaced nasally. The color scale is a relative one, which masks the area of maximal flattening. Figure 8-1-8. (D) Dual Scheimpflug/Placido imaging of the same eye, showing analogous displacement of maximal flattening in anterior curvature, thinnest pachymetry, and anterior elevation. (E) Scheimpflug imaging of the same eye, showing analogous displacement of maximal flattening in anterior curvature and thinnest pachymetry. In this selectable map elevation data are not shown. A patient who underwent PRK for high myopia (≈-8 D) bilaterally complained of reduced visual acuity, ghosting, and loss of BCVA in the right eye. Figure 8-1-9. (A) Scheimpflug composite image from the patient. The right eye has an apparent decentered ablation based on a displaced area of maximal flattening and mild decentration of thinnest pachymetry. The color scale setting skews the degree of decentration, as all values below 39 D have the same dark blue color. In contrast, there is no apparent ablation decentration in the left eye. (B) Scheimpflug composite image showing anterior curvature in [A] Atlas fixed scale, [B] American style absolute scale, and [C] Oculus absolute scale. In both American and Oculus scales, the focal area of flattest curvature is better appreciated. Figure 8-1-9. (C) Scheimpflug refractive display of the same eye. Anterior curvature and pachymetry are the same as shown in previous figures. Anterior elevation shows focal depression in the region just nasal to pupillary center in the regions corresponding with thinnest pachymetry. (D) Scanning slit imaging of the same eye. Anterior curvature and anterior elevation show focal flattening (depression) similar in degree and location as those shown in Scheimpflug imaging. The pachymetry map shows a particularly focal thinnest point that is significantly thinner (260 μm) than that displayed in Scheimpflug imaging (386 μm). (E) Scheimpflug raw image showing a focal area of corneal haze (white arrow) corresponding to the location of thinnest pachymetry seen in scanning slit imaging. Case note: This case nicely demonstrates a pseudodecentered ablation created in appearance by focal corneal haze resulting in irregular astigmatism after surface ablation. This haze negatively impacts the quality of scanning slit imaging and anterior curvature with multiple technologies, with relatively less impact on Scheimpflug pachymetry or elevation displaying. This differentiation is critical as the treatment for visually significant haze and a decentered ablation are markedly different. A patient who underwent SMILE for moderate myopia bilaterally complained of reduced visual acuity, ghosting, glare, and halos in the left eye postoperatively. Figure 8-1-10. Scheimpflug refractive display of the (A) right and (B) left eyes after SMILE. Anterior curvature is notable for a well-centered region of maximal flattening in the right eye consistent with a well-centered myopic treatment and superiorly decentered maximal flattening in the left eye consistent with a decentered treatment. Anterior elevation shows a well-centered maximal depression in the right eye and a superiorly displaced depression in the left eye. Pachymetry maps show an apparently well-centered thinnest point in both eyes. However, thickness 4 mm from center is similar when comparing superior to inferior values and nasal to temporal values in the right eye, while in the left eye there is a significant difference between superior and inferior thicknesses at 4 mm, with superior thinning relative to inferior values. (C) Scheimpflug composite difference maps showing anterior curvature of the right (upper) and left (lower) eyes before (middle) and after (left) SMILE and the total change (right). Difference maps show a well-centered flattening in the right eye and a superiorly decentered maximal flattening in the left eye. Figure 8-1-10. (D) Scheimpflug composite difference maps showing corneal thickness of the right (upper) and left (lower) eyes before (middle) and after (left) SMILE and the total change (right). Difference maps show a well-centered maximal pachymetry reduction in the right eye and a superiorly decentered maximal pachymetry reduction in the left eye. (E) SD-OCT cross section of the left eye. The SMILE interface is easily seen as a continuous hyperreflective line across the cornea. The image is oriented with the superior cornea at the left of the image and the inferior cornea at the right. Superiorly (left) there is slight thickening of the hyperreflectivity in the region corresponding to the tunnel through which the lenticule was removed. Inferiorly (right) there is no change in the thickness or morphology of the hyperreflective band, indicating that there is no retained lenticule tissue. The area of most importance, where retained lenticule tissue could be causing the appearance of decentration, is marked (white arrows). Case note: This case highlights the value of difference maps in determining true treatment decentration from pseudodecentration. In this case, postoperative thinnest pachymetry seemed to indicate a well-centered tissue reduction and therefore a pseudodecentration; however, on examination of pachymetry difference maps the true decentration became clear. SD-OCT imaging confirms the absence of retained lenticule tissue that could potentially cause a pseudodecentration appearance.
Central Islands
Figure 8-1-11. Placido image of the right and left eyes from a patient who underwent myopic LASIK ablation. Anterior curvature is notable for general central flattening within a 6-mm radius consistent with a myopic ablation, but with focal central steepening of ≈2 D in a round pattern in both eyes (black arrow highlights this feature in the left eye). This focal steepening indicates central island formation in both eyes.
Figure 8-1-12. Scanning slit imaging of the left eye from a patient who underwent myopic LASIK ablation. Anterior curvature is notable for focal steepening of 5 D or more within the central 2 mm. Anterior elevation and pachymetry maps are irregular and thus convey no specific information.
Figure 8-1-13. Scanning slit imaging of the left eye from a patient who underwent myopic LASIK ablation. Anterior curvature is notable for general flattening surrounding focal steepening of ≈4 D within the central 2 mm. Anterior elevation is irregular, while pachymetry map shows a well-centered thinnest point consistent with myopic ablation. Figure 8-1-14. (A) Scanning slit imaging of the right eye from a patient who underwent myopic LASIK ablation. Anterior curvature (lower left) is notable for focal steepening of ≈3 D within the central 2 mm. Anterior elevation (upper left) shows a well-centered central depression, and pachymetry mapping (lower right) shows a well-centered thinnest point, both consistent with myopic ablation. (B) Scheimpflug refractive display of the same eye. The findings are analogous to those seen in scanning slit imaging, but it is more challenging to see any focal central steepening in the Scheimpflug anterior curvature map. Figure 8-1-14. (C) Scheimpflug anterior curvature map of the same eye in Atlas fixed scale (left) and Oculus relative 0.25 D scale (right). The focality of the focal steepening (central island) is visible in both scales but easier to identify and quantify in the relative scale. Case note: This case highlights the potential benefit of viewing images in different scales to gain the maximum diagnostic information available.
Ablation Errors
A patient had LASIK for myopia (-8 D in both eyes) with excimer laser ablation stopped and restarted during treatment of the right eye. Postoperatively the patient complained of blurred vision in both eyes, worse in the right eye, and reported frequent headaches. On presentation, UCVA was 20/40 in both eyes. Manifest refraction of -1.00 +0.75 × 095 yielded corrected acuity of 20/25 in the right eye and -4.00 sphere yielded corrected acuity of 20/20 in the left eye. Cycloplegic refraction of +3.00 sphere yielded corrected acuity of 20/20 in the right eye and -0.25 sphere yielded corrected acuity of 20/20 in the left eye.
Figure 8-1-15. (A) Scheimpflug composite image of the patient’s right and left eyes postoperatively. Anterior curvature of the right eye shows a well-centered region of maximal flattening, with central K ≈35 to 36 D, while the left eye shows a mildly decentered region of maximal flattening, with central K ≈39 to 40 D. Pachymetry maps of the right eye show a well-centered thinnest point, with thinnest pachymetry measuring ≈320 μm, while the left eye shows a relatively well-centered thinnest point, with thinnest pachymetry measuring ≈390 μm.
Figure 8-1-15. (B) SD-OCT imaging of the right (upper) and left (lower) eyes from the same patient. Total thickness appears similar to Scheimpflug imaging, with minimum values of 305 μm in the right eye and 381 μm in the left eye. Epithelial mapping shows significantly greater epithelial hypertrophy in the right eye centrally as compared to the left eye. (C) SD-OCT cross-sectional image of the right eye showing a flap thickness of ≈100 to 110 μm and a residual stromal bed (RSB) thickness of ≈210 to 223 μm centrally. Case note: Even without the availability of preoperative corneal imaging, postoperative topographies clearly demonstrate an erroneous overtreatment of the right eye, resulting in significant central flattening, thinning, and resultant hyperopia. The patient’s residual accommodative ability has resulted in their fluctuating refraction and difference between manifest and cycloplegic refractions. Corneal imaging allows for the appropriate diagnosis and thus facilitates making an appropriate subsequent treatment plan. A 45-year-old patient with emmetropia had LASIK performed to improve near vision, with a planned final target of -2 D. However, a -2 D myopic ablation was programmed instead of a hyperopic ablation, resulting in induced hyperopia of +2 D. The patient had retreatment performed and complained of reduced visual quality postoperatively. Figure 8-1-16. (A) Scanning slit imaging of the patient’s right eye following retreatment after initial erroneous ablation. Anterior curvature shows a focal central steepening pattern with a truncated bowtie pattern oriented with the rule. Anterior elevation shows focal elevation corresponding with the area of maximal steepening. Corneal pachymetry shows a relatively well-centered thinnest point of 461 μm. (B) Scheimpflug refractive display of the same eye following retreatment after initial erroneous ablation. Anterior curvature shows a more focal steepening pattern as compared to the Placido map from scanning slit imaging, with steepest K ≈47 to 48 D. Corneal thickness maps are analogous to those from scanning slit imaging. Anterior elevation shows a focal elevation ≈15 μm centrally. A 45-year-old patient with emmetropia underwent LASIK in the right eye only to improve near acuity by inducing monovision but was unable to read postoperatively. There was some confusion as to what caused the vision complaints. Figure 8-1-17. (A) Dual Scheimpflug/Placido difference maps displaying anterior curvature preoperatively (middle), postoperatively (left), and the functional ablation performed through the difference between the 2 (right). Postoperative curvature demonstrates a relative flattening in a symmetric bowtie pattern in against-the-rule orientation. Central flattening induced was -2 D. This confirmed that a myopic ablation pattern had been performed. (B) Scheimpflug refractive display comparison image of the same eye demonstrating the course of events. Preoperative anterior curvature (upper left) became flatter as a result of the erroneous myopic ablation performed (upper middle). Prior to retreatment the patient was monitored to confirm stability over the course of 3 additional months (lower left). After retreatment utilizing a hyperopic ablation pattern (lower middle) the patient ultimately had a net change in corneal power of +2 D (far right) when comparing preoperative (upper left) to final postoperative (lower middle) images. Case note: Difference maps were able to determine the cause of blurred vision (ablation error) and facilitate subsequent treatment planning in this case. A patient had inadvertent ablation error, with a flipped axis resulting in doubling of corneal and refractive astigmatism. Figure 8-1-18. (A) Scheimpflug refractive display of the patient’s left eye. Anterior curvature is notable for a partially truncated bowtie pattern of steepening in an oblique orientation. Simulated anterior corneal astigmatism was measured at 4.5 D, steepest in the 120-degree meridian. Corneal thickness maps displayed a thinnest point of 462 μm. (B) SD-OCT imaging of the same eye. Total thickness was analogous to Scheimpflug imaging, with central thickness of 463 μm and mid-peripheral thickness of 485 to 487 μm. Epithelial maps showed no significant irregularity in epithelial remodeling pattern, with mild thinning in the region of maximal steepening as expected. (C) SD-OCT cross-sectional image displaying regional flap thickness measurements of 106 to 116 μm through most of the flap and RSB thickness more than 350 μm throughout the cornea. Figure 8-1-18. (D) Simulated ablation profile for the same eye. Maximal ablation up to 77 μm would occur in the periphery, with no ablation centrally. (E) Scheimpflug difference map image showing anterior curvature after primary LASIK with incorrect ablation (middle), after LASIK retreatment (left), and the resulting curvature change after ablation (right). Maximal curvature change of 5 D occurred in the periphery. Case note: The combination of Scheimpflug curvature data and SD-OCT regional pachymetry and high-resolution cross-sectional view with flap thickness measurements allows for a safe and successful retreatment in this patient.
SECTION 2: LASIK FLAP COMPLICATIONS
Intraoperative LASIK flap–related complications include the inadvertent creation of excessively thick or thin flaps, buttonhole flaps, free caps, incomplete flaps, and irregular flaps. Femtosecond laser flaps are more predictable in their thickness and morphology than flaps created with a mechanical microkeratome, but flap thickness variation can still occur with any device. Buttonhole flaps and free caps are typically not found in femtosecond laser–created flaps. Postoperative flap complications include flap striae and flap opacities; these complications are also more commonly encountered with microkeratome flaps but can occur with any LASIK procedure.
Thick LASIK Flap
A patient had LASIK for moderate myopia bilaterally 6 months prior with resulting residual myopia in the right eye and sought retreatment for -2.5 D of myopia.
Figure 8-2-1. (A) SD-OCT imaging of the right eye. Total corneal thickness map displays a well-centered thinning pattern consistent with myopic ablation, with a central thickness of 455 μm. Epithelial mapping displayed a regular epithelial pattern with centrally thick values likely due to epithelial hypertrophy after myopic LASIK. Given an estimated flap thickness of 120 μm, the predicted RSB thickness would be more than 330 μm. (B) SD-OCT cross-sectional image displaying regional flap thickness measurements of 190 to 224 μm through the flap and RSB of 240 to 245 μm centrally.
Case note: In this case, SD-OCT flap and RSB thickness measurements were critical to determine that repeat LASIK was less desirable due to excessive flap thickness and low RSB.
Buttonhole Flap
Figure 8-2-2. (A) Slit lamp image of a patient who underwent LASIK flap creation. The case was aborted due to the occurrence of a buttonhole flap (black arrow). (B) Placido image of the same eye in the early postoperative period. There was a focal curvature irregularity in the region of the buttonhole.
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