Postoperative Patterns After Corneal and Refractive Surgery
J. Bradley Randleman, MD; Marcony R. Santhiago, MD, PhD; and William J. Dupps, MD, PhD
Corneal imaging after corneal and refractive surgical procedures presents with unique patterns otherwise not seen, and with greater variations than are typically seen in unoperated corneas without scars or another surface pathology. Corneal imaging is particularly useful and critical for identifying subtle postoperative complications after corneal surgeries. In order to identify those subtleties, one must first be able to recognize variations of normal patterns after a variety of procedures, including keratoplasty, incisional corneal refractive surgery, excimer laser ablative refractive surgery, and corneal imaging after phakic intraocular lens (PIOL) implantation. Being able to accurately identify whether or not a patient had previous refractive surgery and what type of correction was intended is critical for surgical planning for future refractive retreatments, lens calculations and surgical planning at the time of cataract surgery, and ruling in or ruling out previous refractive correction as a cause of visual disturbance, particularly from irregular astigmatism or subtle corneal opacity.
Penetrating keratoplasty (PKP) induces varied topographic patterns after successful surgery. Many patients have high regular and irregular astigmatism; however, some patients have relatively normal postoperative curvature and thickness. Significant fluctuations in shape are common after PKP and deep anterior lamellar keratoplasty (DALK). In contrast, endothelial keratoplasty induces different shape changes, with less overall changes in curvature but greater alterations in thickness, with frequent thickening in cases of Descemet’s stripping automated endothelial keratoplasty (DSAEK) due to graft tissue thickness and thinning following Descemet’s stripping endothelial keratoplasty (DMEK) due to corneal deturgescence with minimal thickening induced from the transplanted tissue.
Figure 7-1-1. Scheimpflug imaging of the (A) right and (B) left eyes from a patient with high refractive astigmatism (10.0 diopters [D] at 165 OD, 9.25 D at 025 OS) after PKP in both eyes. The anterior curvature maps show regular against-the-rule astigmatism in the right eye and asymmetric oblique astigmatism in the left eye. Corneal and refractive astigmatism correlate well in magnitude and orientation in both eyes. Corneal thickness is roughly 80 μm different between the 2 eyes despite equivalent visual function (corrected distance visual acuity = 20/20 OU) and lack of bothersome visual symptoms in either eye. Therefore, these thickness measurements appear normal, albeit quite different, for both corneal grafts and do not appear suggestive of graft failure in the thicker left eye.
Figure 7-1-2. (A) Scheimpflug imaging of the left eye from a patient who developed ectasia after LASIK and underwent PKP. The anterior curvature map is relatively uniform throughout the central cornea, with less than 1 D of corneal astigmatism within the central 4 mm. Corneal thickness appears within normal limits, and elevation imaging is unremarkable. (B) Spectral domain optical coherence tomography (SD-OCT) imaging of the same left eye showing a similar regular total corneal thickness distribution as seen with Scheimpflug imaging.
Figure 7-1-3. (A) Placido imaging for a patient who developed postoperative ectasia after multiple corneal refractive surgeries. Note the significant central and paracentral steepening present in additional to central irregular astigmatism within the visual axis. Figure 7-1-3. (B) Placido imaging of the same patient after undergoing PKP. The pattern is more regular now, but there is now nearly 10 D of oblique regular astigmatism. The graft periphery was highly ectatic as well (not shown). Despite a clear graft the patient did not achieve functional visual acuity and repeat PKP was performed. (C) Placido imaging of the same eye after undergoing repeat PKP. The pattern has now shifted from oblique preoperatively to against the rule, but there is still more than 10 D of regular astigmatism and vision quality was poor. (D) Placido imaging of the same eye with difference maps showing [A] change in astigmatism after selective suture removal, with reduction of simulated astigmatism from 14 D to 7 D and [B] increased astigmatism over time due to graft remodeling without further suture adjustment. Figure 7-1-3. (E) Scheimpflug raw image of the same eye after repeat PKP showing the graft–host interface as hyperreflective regions in the periphery (white arrows). (F) Scheimpflug refractive display of the same eye later in the time course. Anterior curvature shows regular against-the-rule astigmatism, with simulated astigmatism reduced to 7 D. Figure 7-1-3. (G) Scheimpflug difference maps of the same eye over the course of 8 months showing continued shape fluctuation, with more than 3 D of focal flattening centrally in some areas despite no intervention between examinations. Figure 7-1-4. Scheimpflug Holladay report image for a patient who underwent PKP for irregular astigmatism after multiple-cut radial keratotomy (RK). Anterior curvature (upper left) displays a truncated bowtie pattern with up to 5 D of with-the-rule corneal astigmatism centrally. Corneal thickness (upper middle) is regular and within normal limits throughout the graft, while relative pachymetry (lower middle) shows peripheral thickening circumferentially in the region adjacent to the graft–host interface. Elevation maps (right) showing output relative to a best-fit toric ellipsoid shape display significant peripheral elevation in the graft–host interface region. Figure 7-1-5. (A) Scheimpflug raw image showing an eye after DALK for keratoconus. The graft–host interface is visible as a focal hyperreflectivity in the periphery on both sides of the image. Sutures are still in place and are also visible (white arrows). (B) Scheimpflug refractive display of the same eye showing high against-the-rule astigmatism (upper left) with relatively normal post-DALK pachymetry and elevation maps. (C) Placido image of the same eye following suture removal and astigmatic keratotomy incisions that were placed in the 3 and 9 o’clock meridians. There is now induced with-the-rule astigmatism. Figure 7-1-6. (A) Scheimpflug raw images showing an eye following DSAEK. The graft is most easily visible in the periphery (white arrow). Figure 7-1-6. (B) SD-OCT image showing a different eye following DSAEK. As compared to raw Scheimpflug imaging, the graft is much more easily identifiable, with a distinct graft–host interface visible throughout the image (white arrows) and graft edges visible on either side of the image. (C) SD-OCT close-up image of an eye following DSAEK showing the graft–host interface (black arrows) and the edge of the DSAEK graft tissue (white arrow). (Reproduced with permission from Jeff Goshe, MD.) Figure 7-1-7. (A) SD-OCT image of an eye following DMEK showing the barely visible graft–host interface throughout the image (white arrows). DMEK tissue cannot be seen on Scheimpflug raw imaging. (B) SD-OCT close-up image of an eye following DMEK showing the graft–host interface (black arrow). (Reproduced with permission from Craig See, MD.) Figure 7-1-8. SD-OCT image showing an eye following DSAEK performed under PKP graft. The edges of the PKP are marked (white arrows) and the extent of the DSEAK graft is visible. Overall corneal thickness (lower left) is above 600 μm centrally due to the presence of the DSAEK tissue. Epithelial thickness measures are artifactually low in the periphery due to measurement artifact. (Reproduced with permission from Jeff Goshe, MD.) Figure 7-1-9. (A) SD-OCT image showing a DMEK graft (white arrows) in an eye with previous LASIK with the LASIK flap visible (black arrows). (Reproduced with permission from Craig See, MD.) (B) SD-OCT image of the same eye. Central total thickness is low due to previous myopic LASIK, and there is compensatory epithelial hypertrophy centrally. There is minimal added tissue thickness from the DMEK graft, in contrast to previous DSAEK images. (Reproduced with permission from Craig See, MD.) Figure 7-1-10. Scheimpflug composite image of the (A) refractive display from a patient with progressive Fuchs’ dystrophy who underwent DSAEK. Anterior curvature (upper left) and anterior elevation (upper right) remain relatively unchanged after surgery, while corneal thickness (lower left) increases significantly as a result of the graft tissue. Figure 7-1-10. Scheimpflug composite image of the (B) ectasia screening display (middle column) from the same eye. Ectasia screening indices (middle column) all become abnormal after DSAEK. Figure 7-1-10. Scheimpflug composite image of the (C) raw images from the same eye. The DSAEK graft is visible in the postoperative raw image. Figure 7-1-11. (A) Scheimpflug anterior curvature difference maps for the left eye of a patient who underwent DSAEK, showing curvatures before (2015) and after (2018) DSAEK. There is inferior-paracentral steepening of 1 D focally. (B) Scheimpflug corneal thickness difference maps for the same eye. There is central thickening of 45 μm or more and peripheral thickening of greater than 100 μm in the far periphery as a result of DSAEK due to the meniscus shape of the graft. Case note: This case nicely demonstrates comparative findings before and after DSAEK. Note that DSAEK did not significantly alter anterior curvature in this case. Figure 7-1-12. (A) Scheimpflug large map showing anterior curvature in a patient with Fuchs’ dystrophy prior to corneal transplantation. There is focal central steepening with a truncated bowtie pattern along with inferior steepening and Kmax of nearly 50 D. (B) Placido image of the same eye following DMEK. The cornea is significantly flattened with no focal steepening and Kmax of 46 D. (C) SD-OCT image showing total corneal thickness before (left) and after (right) DMEK. Total corneal thickness is reduced by more than 100 µm centrally.
SECTION 2: INCISIONAL REFRACTIVE SURGERY
While less common today, incisional refractive surgery was the primary surgical method for refractive correction for many years; thus, numerous patients present with varying postoperative patterns for evaluation. Many patients remain satisfied with their vision following incisional procedures; however, up to 50% experience a significant hyperopic refractive shift over time and seek out further surgical alternatives for their ametropia. There are classic, recognizable patterns after RK, such as the cloverleaf pattern, but many eyes display remarkably variable patterns after incisional surgery.
Figure 7-2-1. Slit lamp image of an eye with 16-cut RK. (A) Broad illumination highlights the prominent scars and a faint iron deposition centrally, while (B) retroillumination highlights the irregularity of some of the incisions and varied spacing of incisions relative to one another.
Figure 7-2-2. (A) Placido image showing the typical cloverleaf pattern of central flattening commonly present following RK that is seen in axial curvature, mean curvature, elevation, and irregularity maps.
Figure 7-2-2. (B) Dual Scheimpflug/Placido image of an eye with RK showing the same cloverleaf pattern in axial curvature and elevation maps, while the pachymetry map has a normal appearance. (C) Scheimpflug image of an eye with RK showing the same cloverleaf pattern in axial curvature and elevation maps, while the pachymetry map has a normal appearance. Figure 7-2-2. (D) SD-OCT image of an eye with RK showing one of the RK incisions in the raw cross-sectional image (white arrow) and typical epithelial remodeling after RK, with central epithelial hypertrophy due to curvature change despite no removal of corneal tissue. Figure 7-2-3. Placido imaging from a patient who had RK in both eyes. There is central flattening noted in both eyes in axial maps (upper images) with a mildly irregular appearance (a partial cloverleaf-type pattern) in the right eye. A central flattening pattern is more pronounced in tangential maps (lower images), as is the somewhat irregular nature of the optical zone due to the separated radial incisions. Figure 7-2-4. Placido imaging of a left eye from a patient who had RK. A shows the axial map, B shows the tangential map, and C shows the raw ring image. The mild central optical zone irregularity seen in axial imaging is accentuated in tangential mapping. Note there are slight differences in steep K, flat K, and astigmatism between maps due to the differences in calculating these numbers based on axial vs tangential mapping. In the raw ring map, focal discontinuities in the rings (white arrow) highlight the location of the radial incisions. Figure 7-2-5. Scheimpflug anterior curvature imaging of the (A) right and (B) left eyes from a patient who had 8-cut RK in both eyes more than 20 years prior. Both eyes had the same number of incisions, but the resulting topographic patterns are highly disparate. In the right eye, there is significant central flattening that appears decentered inferiorly, with a truncated astigmatic bowtie pattern centrally. In the left eye, there is minimal flattening notable in the axial image; only when viewing the tangential image does the treatment become obvious. Despite these differences, both eyes had minimal residual refractive error and the patient reported visual quality was subjectively good and equal in both eyes. Figure 7-2-5. Scheimpflug refractive displays of the same (C) right and (D) left eyes. In the right eye, there are clear changes in anterior and posterior elevations that correspond well with the central flattening induced by RK and displayed in the anterior curvature map. In the left eye, elevation maps both display indistinct, irregular patterns. Corneal thickness is thinner than average and roughly equivalent between eyes. (E) Dual Scheimpflug/Placido imaging of the right eye from the same patient. Placido tangential curvature (upper left) has a similar appearance to the tangential Scheimpflug map. There is artifactual inferior corneal thinning (lower left) that also transmits to an artifact displayed in the posterior elevation map (lower right). Figure 7-2-6. (A) Scheimpflug refractive display of the left eye from a patient who had 8-cut RK with 2 astigmatic keratotomy incisions. There is central flattening with a cloverleaf type of edge appearance that is typical for RK in the anterior curvature map. Corneal thickness is normal and relatively unaltered, although there is some inferior displacement of the thinnest point. (B) SD-OCT imaging of the same eye. The patient’s total thickness (left) displays a typical distribution pattern for a normal cornea, while the epithelial map shows central hyperplasia resulting from the change in curvature from the myopic incisional surgery and artifactually highlights the irregularities along the incisions (paracentral dark blue areas). In cross section (upper), one of the RK incisions is visible (white arrow). Figure 7-2-7. (A) Slit lamp and (B) Placido imaging of a patient who had hexagonal keratotomy performed to treat hyperopia by inducing central corneal steepening. Note the interconnected paracentral incision creating a hexagonal appearance. Placido topography shows the central steepening of up to 8 D. The optical zone appears relatively well centered, but an extreme overcorrection occurred, leaving the patient with myopia with irregular astigmatism that required a specialty contact lens to correct.
The vast majority of patients who have undergone refractive surgery have had LASIK, so postoperative patterns after LASIK are critical to recognize. While less baseline variability exists between patterns as compared to incisional surgery, there are still a wide variety of patterns that fall within the context of normal postoperative findings.
There are 2 important practical caveats that differentiate incisional and ablative refractive procedures. First, with incisional surgery, incision location (radial vs hexagonal vs tangential) determines the refractive correction; thus, one could predict to some extent the topographic pattern based on slit lamp examination alone. This is not the case with ablative procedures, which all have similar flap dimensions and optical zones. Thus, simply knowing someone had LASIK in the past does not predict the pattern to be found. Second, one can make these topographic pattern predictions after incisional surgery because the incisions are always visible at the slit lamp to the careful observer, and typically are not subtle findings. In contrast, LASIK flaps frequently heal in a manner that makes them nearly imperceptible, even if the observer knows they are there. Thus, recognizing postoperative ablative patterns using corneal imaging is even more critical, as the observer may otherwise not have any other clues that ablation occurred.
Myopic Ablations
Figure 7-3-1. (A) Placido imaging of the left eye from a patient who underwent LASIK for the correction of myopia (myopic LASIK). Axial curvature (left) shows a generalized flat pattern centrally, while tangential curvature (right) shows distinct central flattening surrounded by focal steepening in the periphery around the edge of the treatment zone.
Figure 7-3-1. (B) Placido difference maps of the same left eye show preoperative curvature (upper left), postoperative curvature (lower left), and the resulting curvature difference due to ablation (right). This patient had 2 D of myopic ablation. Figure 7-3-2. (A) Scheimpflug comparative imaging from a patient who underwent myopic LASIK in both eyes. This patient had significantly higher myopia in the left eye than the right eye. While one needs difference maps to be able to accurately determine the difference in ablation, postoperative central curvature values and flattening pattern (upper images) provide some clues to the extent of the ablation performed, as do differences in central corneal thickness (lower images). (B) Scheimpflug refractive display of the right eye from the same patient. Axial curvature shows central flattening, central corneal thickness is thin, and anterior elevation is flat (negative) centrally. These findings are all consistent with a myopic ablation, where tissue is ablated centrally to reduce central corneal curvature and, thus, central corneal refractive power. Figure 7-3-2. Scheimpflug difference maps of the (C) right and (D) left eyes from the same patient before and after myopic ablation. Comparing preoperative (middle image) to postoperative (left image) curvature, in the right eye, 2 D of refractive change was induced (right image), while in the left eye, 6 D of myopic correction was performed. Figure 7-3-2. SD-OCT imaging of the (E) right and (F) left eyes from the same patient before and after myopic ablation. In the right eye, total central corneal thickness was reduced by 28 μm, while in the left eye, almost 90 μm of ablation was performed. Differences in ablations are apparent in the epithelial maps, where minimal epithelial remodeling has occurred in the right eye (3 to 5 μm of central thickening across the optical zone) as compared to the left eye (8 to 10 μm of central thickening across the optical zone). Figure 7-3-2. Scheimpflug Zernike composite images of the (G) right and (H) left eyes [A] before and [B] after LASIK. The major aberrations that have been reported to affect vision quality are highlighted in the right boxes (trefoil, coma, and spherical aberration). There are minimal differences in any of these aberrations following wavefront-optimized LASIK. Figure 7-3-3. (A) Dual Scheimpflug/Placido imaging of a patient who underwent myopic LASIK. Note the typical central flattening pattern (upper left), with central thinning (upper right). (B) Dual Scheimpflug/Placido difference maps showing before (middle) and after (left) ablation, with the resulting difference in curvature displayed (right). Preoperatively, the patient had approximately 1.5 D of corneal astigmatism. The difference map shows a compound myopic and astigmatic treatment, with a central reduction of approximately 6 D, with approximately 7.5 D of maximal change in the 90-degree meridian as compared to 6 D in the horizontal meridian. The resulting postoperative pattern (left) is a nearly spherical cornea.
Hyperopic Ablations
Figure 7-3-4. Placido imaging of the right and left eyes from a patient who underwent LASIK for the correction of hyperopia (hyperopic LASIK). Axial curvature (upper) shows a generalized steep pattern centrally in both eyes, much more pronounced in the left eye, while mean curvature values (lower) show a similar pattern but with a more pronounced central focal steepening in both eyes.
Figure 7-3-5. Scheimpflug refractive displays of the (A) right and (B) left eyes from a patient who underwent hyperopic LASIK. While some variation in pattern exists between eyes, axial curvature shows central steepening, central corneal thickness is minimally altered, peripheral corneal thickness does appear irregular as compared to a typical unoperated cornea in both eyes and anterior elevation is steep (positive) centrally. These findings are all consistent with a hyperopic ablation, where tissue is ablated, peripherally to increase central corneal curvature and, thus, central corneal power.
Figure 7-3-5. Scheimpflug difference maps of the (C) right and (D) left eyes from the same patient before and after hyperopic ablation. Comparing preoperative (middle image) to postoperative (left image) curvature, in the right eye, approximately 2 to 3 D of refractive change was induced (right image), while in the left eye, approximately 2.5 D of hyperopic correction was performed. The treatment appears well centered in the left eye but slightly displaced temporally in the right eye. Figure 7-3-5. Scheimpflug Zernike displays of the (E) right and (F) left eyes postoperatively. There are no preoperative maps for comparison. As compared to the myopic ablation seen earlier (Figures 7-3-2G and H), there is higher trefoil and lower spherical aberration after this hyperopic LASIK case, with negative spherical aberration in the right eye. Figure 7-3-6. (A) Scheimpflug refractive displays of the right eye from a patient who underwent hyperopic LASIK. The pattern is similar to the previous case, with axial curvature showing central steepening, central corneal thickness appears minimally altered, and anterior elevation is steep (positive) centrally. Scheimpflug difference maps of the (B) right and (C) left eyes from the same patient at 2 postoperative time points 4 years apart. In both eyes, there has been regression of the treatment effect. Comparing preoperative (middle image) to postoperative (left image) curvature, in the right eye, approximately 1 D of refractive change occurred (right image, shown as -1 D centrally, indicating flattening), while in the left eye, approximately 1.5 D of refractive change occurred (right image, shown as -1.5 D centrally, indicating flattening).
Astigmatic Ablations
Figure 7-3-7. (A) Placido difference maps of the left eye of a patient who underwent LASIK for the correction of astigmatism. Preoperative curvature (upper left) shows high with-the-rule astigmatism, postoperative curvature (lower left) shows minimal residual with-the-rule astigmatism, and the resulting difference in curvature due to ablation (right) shows approximately 3 D of ablation resulting in flattening of the steep meridian. (B) Placido imaging showing longitudinal difference maps of the same left eye at 3 time points. The first 2 top images are pre (left) and post (middle) ablation, with the resulting difference shown in the lower left image. The lower right image shows no change in curvature over 2 years postoperatively (difference between top middle and right images).
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