Recurrence of keratoconus characteristics: a clinical and histologic follow-up analysis of donor grafts

Characterisation of ectasia after penetrating keratoplasty in keratoconus eyes using anterior segment optical coherence tomography

BACKGROUND/AIMS

Ectasia of the cornea can occur decades after penetrating keratoplasty (PK), especially in keratoconus eyes. The purpose of this study was to characterise ectasia after PK by morphological findings in anterior segment optical coherence tomography (AS-OCT).

METHODS

In this retrospective, single-centre case series, 50 eyes of 32 patients with a history of PK at an average of 25±10 years earlier were included. The eyes were classified either as ectatic (n=35) or as non-ectatic (n=15). The main parameters included central corneal thickness (CCT), lowest corneal thickness at the interface (LCTI), anterior chamber depth, graft-host interface angle at the thinnest point and host cornea-iris angle. Furthermore, steep and flat keratometry readings obtained by AS-OCT (CASIA-2, Tomey) and Scheimpflug tomography (Pentacam, Oculus) were assessed. OCT findings were correlated with clinical grading of ectasia.

RESULTS

There was a highly significant difference in LCTI, graft-host interface angle and anterior chamber depth (in pseudophakic eyes) between the groups. The ratio calculated by the quotient of LCTI divided by CCT was significantly lower in ectatic than non-ectatic eyes (p<0.001). In eyes with an LCTI/CCT ratio of ≤0.7, the OR for the occurrence of a clinical detectable ectasia was 2.4 (CI 1.5 to 3.7). Steep keratometry values were significantly higher in ectatic eyes.

CONCLUSION

AS-OCT is a helpful tool to recognise and quantify ectasia in post-PK eyes objectively.

Corneal cross-linking for treatment of keratoconus relapse in post-keratoplasty eyes

PURPOSE

Keratoconus relapse after penetrating keratoplasty is a rare condition that may result in severe visual deterioration and corneal graft thinning. Therefore, treatment to stabilize the cornea should be considered. The purpose of this study was to evaluate the safety and efficacy of Corneal Cross-Linking (CXL) in eyes with relapse of keratoconus after penetrating keratoplasty for keratoconus.

MATERIALS AND METHODS

A retrospective review of eyes that developed keratoconus relapse following a penetrating keratoplasty and treated with CXL. The main outcome measures were change in maximal keratometry (Kmax), best-corrected distance visual acuity (BCVA), thinnest corneal thickness (TCT) and central corneal thickness (CCT), and complications.

RESULTS

We identified 10 consecutive eyes of 9 patients. Preoperative median BCVA before the CXL and 1 year after the CXL procedure remained stable (p = 0.68). The median (IQR) of Kmax improved from 63.2 (24.9) D before the CXL procedure to 62.2 (27.1) D at 1 year postoperatively (P = 0.028). Median TCT and CCT also remained with no significant change 1 year after CXL. No complications were noted following the procedure.

CONCLUSION

CXL in eyes with keratoconus relapse after keratoplasty is a safe and effective procedure enabling not only visual stabilization but also might bring keratometry improvement. Routine follow-up after keratoplasty should be performed for early detection of keratoconus relapse and CXL is timely advised when such a relapse is documented.

Therapeutic non-ectasia applications of cornea cross-linking

Corneal cross-linking is a photopolymerization technique traditionally used to strengthen corneal tissue. Corneal cross-linking utilizes riboflavin (vitamin B2) as a photosensitizer and ultraviolet-A light (UVA) to create strong covalent bonds within the corneal stroma, increasing tissue stiffness. Multiple studies have demonstrated corneal cross-linking's effectiveness in treating corneal ectasia, a progressive, degenerative, and non-inflammatory thinning disorder, as quantified by key tomographic, refractive, and visual parameters. Since its introduction two decades ago, corneal cross-linking has surpassed its original application in halting corneal ectatic disease and its application has expanded into several other areas. Corneal cross-linking also possesses antibacterial, antienzymolytic and antioedematous properties, and has since become a tool in treating microbial keratitis, correcting refractive error, preventing iatrogenic ectasia, stabilising bullous keratopathy and controlling post keratoplasty ametropia. This review provides an overview of the current evidence base for the therapeutic non-ectasia applications of cornea cross-linking and looks at future developments in the field.

Recurrent keratoconus: an analysis of breaks in Bowman's layer in corneal grafts

OBJECTIVE

To study in a masked fashion whether an objective histological feature associated with keratoconus (KCN) occurs in donor corneas in eyes originally receiving a corneal graft for KCN.

METHODS

Two ocular pathologists performed a retrospective masked histological analysis of slides from donor buttons recovered from 21 eyes with a history of KCN undergoing repeat penetrating keratoplasty (failed-PK-KCN), 11 eyes that underwent their first PK due to KCN (primary KCN), and 11 eyes without history of KCN which underwent PK for other conditions (failed-PK-non-KCN). Breaks/gaps in Bowman's layer served as the pathological feature indicative of recurrent KCN.

RESULTS

Breaks in Bowman's layer were present in 18/21 (86%) of the failed-PK-KCN group, 10/11 (91%) of the primary KCN group, and in 3/11 (27%) of the failed-PK-non-KCN group. Pathological evidence suggests that the prevalence of breaks is significantly higher in grafted patients with a history of KCN than non-KCN controls (OR: 16.0, 95% CI 2.63 to 97.2, Fisher's exact test p=0.0018) with a conservative Bonferroni criterion of p <0.017 to account for multiple group comparisons. There was no statistically significant difference found between the failed-PK-KCN and primary KCN groups.

CONCLUSIONS

This study provides histological evidence that breaks and gaps in Bowman's layer, consistent with those found in primary KCN, may develop within the donor tissue in eyes with a history of KCN.

Analysis of visual and refractive results after wedge resection for high astigmatism after penetrating keratoplasty in keratoconus

PURPOSE

To analyze visual and refractive results after wedge resection to correct high astigmatism after penetrating keratoplasty (PK) for keratoconus.

SETTING

Cornea Unit of the Centro de Oftalmología Barraquer Barcelona, Spain.

DESIGN

A retrospective quasi-experimental, before and after study.

METHODS

Patients who developed high astigmatism or ectasia in the graft-host junction after PK were treated with wedge resection. The following variables were studied before the surgery, 1-year after and at the final visit: uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive and topographic astigmatism and spherical equivalent. Vectorial analysis of the astigmatism changes was performed.

RESULTS

Fifty-one eyes were included with a mean follow-up of 4.19 ± 3.09 years. Mean refractive astigmatism was 11.47 ± 3.57 diopters (D) pre-operatively and 4.79 ± 3.32 D at the final follow-up (p < 0.001). The mean centroid changed from 2.65 ± 11.82 D at 23 degrees preoperatively to 0.35 ± 5.86 D at 127 degrees postoperatively. Concerning spherical equivalent, the mean preoperative value was -3.10 ± 4.15 D and the mean postoperative value was -1.55 ± 3.41 D (p = 0.002). Mean pre-operative and final follow-up UDVA were 1.25 ± 0.27 and 0.84 ± 0.50 (p < 0.001). Mean Pre-op and final follow-up CDVA were 0.27 ± 0.19 and 0.24 ± 0.24.

CONCLUSIONS

Wedge resection is a useful surgical procedure to correct high astigmatism. It is a safe technique with moderate efficacy and may be considered as initial procedure of choice in high astigmatism due to long-term ectasia in the graft-host junction after PK for keratoconus.

Post Penetrating Keratoplasty Ectasia: Incidence, Risk Factors, Clinical Features, and Treatment Options

BACKGROUND: Corneal transplantation in keratoconus (KC) patients is generally considered to be successful with a high grade of patient satisfaction. Long-term studies suggest a 6% to 11% probability of KC recurrence manifested by keratometric instability and progressive corneal ectasia. METHODS: We propose to review the frequency, risk factors for the development, and the surgical options for the correction of high irregular astigmatism due to late graft ectasia following penetrating keratoplasty (PK). RESULTS: Post-keratoplasty ectasia is characterized by increasing corneal steepening with myopic shift and high irregular astigmatism, developing years or decades after PK, mostly occurring in KC patients. Contact lenses may adequately improve the visual acuity; however, because these patients are often elderly and intolerant to hard contact lenses, ultimately a surgical correction is proposed to the patient. Compressive suture and corneal wedge resection may improve corneal astigmatism, but the outcomes are unpredictable and often temporary. For this reason, a larger PK graft is often proposed for surgical rehabilitation with the consequence of removing more of the recipient’s healthy endothelium and exposing the patient to a renewed immunogenic stimulus and short-term graft failure for endothelial decompensation. More recently, lamellar keratoplasty using various techniques has been proposed as an alternative to PK in order to maximize the visual outcomes and minimize the complications. CONCLUSIONS: Management of advanced corneal ectasia is a significant challenge for corneal surgeons. Many surgical approaches have been developed, so there is a large arsenal of surgical operations to correct post-PK ectasia. Among them, large-diameter anterior lamellar keratoplasty may be a viable, safer, and effective alternative to PK for the correction of post-keratoplasty ectasia.

Anterior pituitary, sex hormones, and keratoconus: Beyond traditional targets

"The Diseases of the Horny-coat of The Eye", known today as keratoconus, is a progressive, multifactorial, non-inflammatory ectatic corneal disorder that is characterized by steepening (bulging) and thinning of the cornea, irregular astigmatism, myopia, and scarring that can cause devastating vision loss. The significant socioeconomic impact of the disease is immeasurable, as patients with keratoconus can have difficulties securing certain jobs or even joining the military. Despite the introduction of corneal crosslinking and improvements in scleral contact lens designs, corneal transplants remain the main surgical intervention for treating keratoconus refractory to medical therapy and visual rehabilitation. To-date, the etiology and pathogenesis of keratoconus remains unclear. Research studies have increased exponentially over the years, highlighting the clinical significance and international interest in this disease. Hormonal imbalances have been linked to keratoconus, both clinically and experimentally, with both sexes affected. However, it is unclear how (molecular/cellular signaling) or when (age/disease stage(s)) those hormones affect the keratoconic cornea. Previous studies have categorized the human cornea as an extragonadal tissue, showing modulation of the gonadotropins, specifically luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Studies herein provide new data (both in vitro and in vivo) to further delineate the role of hormones/gonadotropins in the keratoconus pathobiology, and propose the existence of a new axis named the Hypothalamic-Pituitary-Adrenal-Corneal (HPAC) axis.

The role of environment in the pathogenesis of keratoconus

PURPOSE OF REVIEW

This study was conducted to demonstrate the importance of the environment in keratoconus (KC) genesis.

RECENT FINDINGS

Genetic-related connective tissue disorders demonstrate the inconsistency of theories regarding KC pathogenesis since no corneal steepening was observed in the majority of these patients. Despite recent advances and decades of research into the genetics of KC, the identification of disease-causing KC genes has been frustrating. Variants found based on genome-wide and next-generation sequencing only seem to account for a small number of cases or play a limited role in KC pathogenesis.

SUMMARY

The literature shows that mechanical manipulation may be the common underlying factor or the indispensable act precipitating the cascade of events leading to permanent corneal deformation. Hence, ophthalmologists have the opportunity to increase patient awareness about eye manipulation repercussions and treatment for ocular surface disorders.

VIDEO ABSTRACT

http://links.lww.com/COOP/A42.

Posterior Chamber Phakic Intraocular Lens Implantation for Refractive Correction in Corneal Ectatic Disorders: A Review

PURPOSE

To summarize the indications and outcomes of posterior chamber phakic intraocular lens (PIOL) implantation in corneal ectasias including keratoconus, pellucid marginal degeneration (PMD), post-refractive surgery, and post-keratoplasty ectasias.

METHODS

A review of the literature was conducted using the relevant keywords from various databases up to August 15, 2020. All pertinent studies were reviewed, and the relevant articles were studied in detail for efficacy, stability, predictability, and safety outcomes. In addition, visual quality, corneal biomechanical outcomes, complications, the role of posterior chamber PIOL in combination treatment, and comparison of posterior chamber PIOL with other PIOLs for ectasias were also evaluated.

RESULTS

A total of 30 relevant studies (13 prospective, 13 retrospective, 4 case reports) on the subject were studied and summarized. All studies showed a favorable refractive outcome. Quality of vision remained unaffected and no significant complications were reported in any of the studies.

CONCLUSIONS

Posterior chamber PIOLs represent a viable option in the treatment of mild to moderate and stable corneal ectasia in patients with contact lens intolerance who have low irregular astigmatism, a clear central cornea, and good preoperative corrected distance visual acuity. [J Refract Surg. 2021;37(5):351-359.].

Ten-year outcomes of microkeratome-assisted lamellar keratoplasty for keratoconus

BACKGROUND/AIMS

To report the 10-year outcomes of modified microkeratome-assisted lamellar keratoplasty (LK) for keratoconus.

METHODS

In this single-centre interventional case series, 151 consecutive eyes with keratoconus underwent modified microkeratome-assisted LK. Eyes with scars extending beyond the posterior half of the corneal stroma and preoperative thinnest-point pachymetry value of less than 300 μm were excluded. Outcome measures were best spectacle-corrected visual acuity (BSCVA), refractive astigmatism (RA), endothelial cell density, immunological rejection, ectasia recurrence and graft failure rates.

RESULTS

Baseline BSCVA (0.89±0.31 logarithm of the minimum angle of resolution (logMAR)) significantly improved to 0.10±0.12 logMAR at year 3 (p<0.001), and remained stable up to 10 years. At 10 years, 94% of eyes saw ≥20/40, 61% saw ≥20/25 and 24% saw ≥20/20 Snellen BSCVA. At final follow-up, RA exceeding 4.5 dioptres was observed in 5 cases (4%). Endothelial cell loss was 25±17% at 1 year with an annual decline of 2% over 10 years. The 10-year cumulative risk for immunological rejection and graft failure was 8.5%, and 2.4%, respectively. No case developed recurrent ectasia at 10 years.

CONCLUSION

Modified microkeratome-assisted LK results in stable visual and refractive outcomes with low rates of immunological rejection and graft failure in the absence of recurrence of ectasia for at least 10 years.

Sphere-forming corneal cells repopulate dystrophic keratoconic stroma: Implications for potential therapy

BACKGROUND

Keratoconus is a degenerative corneal disease characterised by aberrant cell behaviour and loss of matrix that can result in vision loss. Cells extracted from peripheral corneas can form stem cell-enriched spheres, which have shown the potential to repopulate the normal peripheral corneal stroma in vitro upon sphere implantation but have not been previously studied in keratoconic tissue.

AIM

To investigate the therapeutic potential of stem cell-enriched spheres formed from extracted peripheral human corneal cells when introduced to keratoconic tissue.

METHODS

Stem cell-enriched spheres were formed from extracts of normal cadaveric human peripheral corneal cells. These spheres were implanted into incisions created in full thickness and onto the surface of 10 µm thin sections of keratoconic and normal stromal tissues in vitro. Tissue sections were used to maximise use of limited keratoconic tissue available for research. Living cells were stained with Calcein-AM and visualised with stereo and fluorescence microscopy to assess survival and behaviours between the time of implantation day 0 and 14 d (D14) from implantation. Sphere cells in implanted tissues were characterised for stem cell and differentiation markers using immunohistochemistry and droplet digital PCR to assess the potential implications of these characteristics in the use of spheres in keratoconus treatment.

RESULTS

Spheres were successfully implanted into full-thickness central corneal tissue and onto the surface of 10 µm thin en face tissue sections. No observable differences were seen in sphere migration, proliferation or differentiation in keratoconic tissue compared to normal between day 0 and D14. Spheres stained positively with Calcein-AM up to D14. Cell migration increased from day 0 to D14, occurring radially in three dimensions from the sphere and in alignment with tissue edges. Cell proliferation marker, EdU, was detected at day 10. Implanted spheres stained positively for putative stem cell markers ∆Np63α and ABCB5, while ABCG2, ABCB5, ∆Np63 and p63α were detectable by droplet digital PCR up to D14. Double immunolabelling revealed absence of ABCB5 staining in migrated cells but positive staining of alpha smooth muscle actin (myofibroblast marker) in some migrated cells. Droplet digital PCR showed similar expression patterns of differentiation markers but a reduction in stem cell markers between normal and keratoconic tissue with an increase in stromal cell markers and a reduction in epithelial cell markers, indicating an appropriate response to repopulating diseased tissue.

CONCLUSION

Cells from implanted stem cell-enriched spheres can repopulate a keratoconic corneal stromal surface in a directed manner and exhibit migratory stromal cell phenotypes.

Genetic Aspects of Keratoconus: A Literature Review Exploring Potential Genetic Contributions and Possible Genetic Relationships with Comorbidities

INTRODUCTION

Keratoconus (KC) is a complex, genetically heterogeneous, multifactorial degenerative disorder that is accompanied by corneal ectasia which usually progresses asymmetrically. With an incidence of approximately 1 per 2000 and 2 cases per 100,000 population presenting annually, KC follows an autosomal recessive or dominant pattern of inheritance and is, apparently, associated with genes that interact with environmental, genetic, and/or other factors. This is an important consideration in refractive surgery in the case of familial KC, given the association of KC with other genetic disorders and the imbalance between dizygotic twins. The present review attempts to identify the genetic loci contributing to the different KC clinical presentations and relate them to the common genetically determined comorbidities associated with KC.

METHODS

The PubMed, MEDLINE, Google Scholar, and GeneCards databases were screened for KC-related articles published in English between January 2006 and November 2017. Keyword combinations of "keratoconus," "risk factor(s)," "genetics," "genes," "genetic association(s)," and "cornea" were used. In total, 217 articles were retrieved and analyzed, with greater weight placed on the more recent literature. Further bibliographic research based on the 217 articles revealed another 124 relevant articles that were included in this review. Using the reviewed literature, an attempt was made to correlate genes and genetic risk factors with KC characteristics and genetically related comorbidities associated with KC based on genome-wide association studies, family-based linkage analysis, and candidate-gene approaches.

RESULTS

An association matrix between known KC-related genes and KC symptoms and/or clinical signs together with an association matrix between identified KC genes and genetically related KC comorbidities/syndromes were constructed.

CONCLUSION

Twenty-four genes were identified as potential contributors to KC and 49 KC-related comorbidities/syndromes were found. More than 85% of the known KC-related genes are involved in glaucoma, Down syndrome, connective tissue disorders, endothelial dystrophy, posterior polymorphous corneal dystrophy, and cataract.

Immunologic Stromal Rejection After Deep Anterior Lamellar Keratoplasty With Grafts of a Larger Size (9 mm) for Various Stromal Diseases

PURPOSE

To evaluate the rate and outcomes of immunologic stromal rejection occurring after large deep anterior lamellar keratoplasty (DALK) and the effect of the underlying disease on the cumulative probability of rejection.

METHODS

This was a retrospective chart review of all eyes that underwent a 9-mm DALK at Ospedali Privati Forlì (Forlì, Italy). On the basis of preoperative diagnosis, eyes were assigned to group 1: keratoconus, group 2: stromal disease with a low risk for rejection, or group 3: stromal disease with a high risk for rejection. The cumulative probability of experiencing a rejection episode over time was assessed by Kaplan-Meier analysis and was compared among the 3 groups using the log-rank test. Values of corrected distance visual acuity, central corneal thickness, and endothelial cell density before and 6 months after rejection were compared.

RESULTS

Twenty of 377 eyes (5.3%) experienced an episode of stromal rejection [17/265 (6.4%) in group 1, 2/71 (2.8%) in group 2, and 1/41 (2.4%) in group 3]. The mean time interval between DALK and the rejection onset was 11.8 months (range 1-24). The cumulative probability of rejection episodes did not differ significantly among the 3 groups. All episodes resolved within 6 months after the onset, with no significant differences between prerejection and 6-month postrejection values of corrected distance visual acuity, central corneal thickness, and endothelial cell density.

CONCLUSIONS

The rate of immunologic stromal rejection after large 9-mm DALK is within the range reported in the literature for conventional DALK, regardless of the indication for surgery.

Use of Donors Predisposed by Corneal Collagen Cross-linking in Penetrating Keratoplasty for Treating Patients With Keratoconus

PURPOSE

To investigate whether use of donors predisposed by corneal collagen cross-linking (CXL) reduced myopic refractive errors for keratoconic eyes after penetrating keratoplasty (PK).

DESIGN

Randomized controlled trial.

METHODS

One hundred sixteen eyes of 116 patients with keratoconus from Zhongshan Ophthalmic Center were enrolled. Using stratified block randomization, we assigned eligible eyes to the CXL graft group (Group 1) or conventional graft group (Group 2). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent (SE), and topographic data were compared 12, 24, and 36 months after surgery.

RESULTS

Group 1 had better UDVA and CDVA than Group 2 after 1 year follow-up. Also, Group 1 had a lesser degree of SE and lower manifest cylinder than Group 2. At 3 years follow-up, mean CDVA was 0.17 ± 0.10 logarithm of the minimum angle of resolution (logMAR) in Group 1 vs 0.23 ± 0.12 logMAR in Group 2 (P = .004). Mean SE was -3.50 ± 2.93 diopter (D) in Group 1 and -4.02 ± 2.57 D in Group 2 (P = .034). Mean manifest cylinder was -5.22 ± 2.64 D and -6.35 ± 2.80 D in Group 1 and Group 2, respectively (P = .013). At 3 years follow-up, simulated keratometry in the steepest meridian (Kmax) was 46.85 ± 2.85 D vs 49.37 ± 2.92 D (P = .036); corneal power was 44.41 ± 2.89 D vs 46.35 ± 2.87 D (P = .001); and keratometric astigmatism was 4.53 ± 1.06 D vs 5.98 ± 1.28 D (P < .001) in Group 1 and Group 2, respectively.

CONCLUSIONS

Use of donors predisposed by CXL could reduce topographic readings after PK for the treatment of keratoconus, and consequently reduce myopic refractive errors and improve visual acuity.

Deep Anterior Lamellar Keratoplasty followed by Toric Lens Implantation for the Treatment of Concomitant Anterior Stromal Diseases and Cataract

Purpose

To evaluate the outcomes of deep anterior lamellar keratoplasty (DALK) followed by phacoemulsification and toric intraocular lens (IOL) implantation for the treatment of concomitant stromal disease and cataract.

Methods

In this retrospective non-comparative interventional case series, ten eyes affected by stromal disease and cataract underwent DALK followed by phacoemulsification with toric IOL implantation after a minimum period of 5 months from complete suture removal. In each case, topographic astigmatism, refraction, visual acuity, and endothelial cell density were recorded before DALK and 1, 6, and 12 months after cataract surgery. In addition, IOL rotation was evaluated using anterior segment optical coherence tomography.

Results

Big-bubble DALK was performed in all eyes but one that received manual dissection. Topographic astigmatism averaged 5.6 ± 2.2 diopters (D) after suture removal; refractive astigmatism decreased to 0.55 ± 0.61 D as early as one month after cataract surgery and did not change substantially throughout the follow-up period. In all patients, one month after phacoemulsification uncorrected and best spectacle-corrected visual acuity were, respectively, ≥20/40 and ≥20/25 with a residual spherical equivalent of 0.00 ± 0.84 D. At the latest follow-up visit, in all cases the IOL rotation was ≤5 degrees from the intended position and the endothelial cell loss within 8.5%. No complications were recorded.

Conclusions

DALK followed by phacoemulsification with toric IOL implantation optimizes visual and refractive outcomes in patients with concomitant stromal disease and cataract. In comparison with a combined procedure, the sequential approach offers better predictability of the postoperative refraction in the absence of an increased risk of complications.

A review of keratoconus: Diagnosis, pathophysiology, and genetics

We discuss new approaches to the early detection of keratoconus and recent investigations regarding the nature of its pathophysiology. We review the current evidence for its complex genetics and evaluate the presently identified genes/loci and potential candidate gene/loci. In addition, we highlight current research methodologies that may be used to further elucidate the pathogenesis of keratoconus.

Corneal Sublayers Thickness in Patients With Mitral Valve Prolapse

OBJECTIVES

The aim of this study was to compare the thickness of each corneal sublayer in patients with mitral valve prolapse (MVP) and healthy individuals.

METHODS

A total of 38 eyes from 38 patients with MVP and 34 eyes from 34 age- and sex-matched healthy individuals were included in this study. The thickness of the corneal epithelium, Bowman layer, stroma, and Descemet membrane-endothelium complex were measured on the central cornea (i.e., corneal apex) and both the inferior and superior halves of the cornea with anterior segment module of spectral domain optical coherence tomography.

RESULTS

No statistically significant differences emerged between the study and control groups in terms of Bowman layer thickness in the central cornea and the cornea's superior half (P=0.092 and P=0.128, respectively). However, in the inferior half of the cornea, Bowman layer thickness among patients with MVP was 11.95±2.34 μm (range 7-16 μm) and in the control group was 13.03±1.62 μm (range 10-16 μm), which made for a statistically significant difference (P=0.025).

CONCLUSIONS

Our study revealed thinning of Bowman layer in the inferior half of the cornea in patients with MVP.

Corneal surgery in keratoconus: which type, which technique, which outcomes?

Keratoconus is a disease characterized by progressive thinning, bulging, and distortion of the cornea. Advanced cases usually present with loss of vision due to high irregular astigmatism. A majority of these cases require surgical intervention. This review provides an update on the current treatment modalities of corneal surgery available for the management of advanced corneal ectasias.

Comparison of refractive outcomes in three corneal transplantation techniques for keratoconus

BACKGROUND

Deep anterior lamellar keratoplasty (DALK) has a much lower incidence of immunologic reactions than penetrating keratoplasty (PK) for patients with keratoconus. However, it is unclear whether DALK is better on refractive outcomes than PK, due to its high postoperative myopia.

METHODS

We retrospectively studied the clinical records of keratoconus patients who underwent PK, DALK, or predescemetic DALK (pre-DALK, DALK with residual stroma) between June 2004 and September 2008. The main outcome measures included refractive sphere, manifest cylinder, corneal power, keratometric astigmatism, and best-corrected visual acuity (BCVA) at the latest visit and the methods of visual correction. Postoperative manifest refractions and topography data were compared at postoperative 3, 5, 7, and 9 years among the three groups. Additionally, the final BCVA and the methods of vision correction were compared.

RESULTS

A total of 172 subjects (172 eyes) screened out of 207 keratoconus patients underwent PK (79 eyes), DALK (68 eyes), or pre-DALK (25 eyes). Postoperative myopic refractive sphere increased in all groups, but the most obvious increase was noted in the pre-DALK group. At the 9-year follow-up, both the pre-DALK group (-6.5 ± 1.7 D) and DALK group (-6.1 ± 1.8 D) had higher myopic refractive sphere than the PK group (-5.0 ± 1.5 D, p < 0.05). Postoperative myopic manifest astigmatism progressively increased in 5 years, but there were no differences among the groups. The progressive increases in postoperative corneal power were recorded in all groups, with the highest one in the pre-DALK group and the lowest in the PK group. At the 9-year follow-up, both the pre-DALK (49.8 ± 2.7 D) and DALK (48.8 ± 2.1 D) groups had higher corneal power than the PK group (47.3 ± 2.0 D); meanwhile, the corneal power was higher in the pre-DALK group than the DALK group (p < 0.05). No differences were noted with respect to keratometric astigmatism among the groups. Mean LogMAR BCVA was 0.12 ± 0.12 in the DALK group, 0.17 ± 0.10 in the pre-DALK group, and 0.1 ± 0.11 in the PK group (p = 0.325) at 9 years after surgery. Moreover, the methods of achieving BCVA seem to be similar among the treatment groups.

CONCLUSIONS

Although DALK has a slightly higher degree of myopic refraction than PK, DALK and PK have comparable visual acuity outcomes and similar methods of vision correction. DALK is recommended for the treatment of keratoconus.

Treatment options for advanced keratoconus: A review

Traditionally, the mainstay of treatment for advanced keratoconus (KC) has been either penetrating or deep anterior lamellar keratoplasty (PK or DALK, respectively). The success of both operations, however, has been somewhat tempered by potential difficulties and complications, both intraoperatively and postoperatively. These include suture and wound-healing problems, progression of disease in the recipient rim, allograft reaction, and persistent irregular astigmatism. Taken together, these have been the inspiration for an ongoing search for less troublesome therapeutic alternatives. These include ultraviolet crosslinking and intracorneal ring segments, both of which were originally constrained in their indication exclusively to eyes with mild to moderate disease. More recently, Bowman layer transplantation has been introduced for reversing corneal ectasia in eyes with advanced KC, re-enabling comfortable contact lens wear and permitting PK and DALK to be postponed or avoided entirely. We offer a summary of the current and emerging treatment options for advanced KC, aiming to provide the corneal specialist useful information in selecting the optimal therapy for individual patients.

The use of Bowman's layer vertical topographic thickness map in the diagnosis of keratoconus

PURPOSE

To evaluate the use of Bowman's layer (BL) vertical topographic thickness maps in diagnosing keratoconus (KC).

DESIGN

Prospective, case control, interventional case series.

PARTICIPANTS

A total of 42 eyes: 22 eyes of 15 normal subjects and 20 eyes of 15 patients with KC.

INTERVENTION

Bowman's layer 2-dimensional 9-mm vertical topographic thickness maps were created using custom-made ultra high-resolution optical coherence tomography.

MAIN OUTCOME MEASURES

Bowman's layer average and minimum thicknesses of the inferior half of the cornea, Bowman's ectasia index (BEI; defined as BL minimum thickness of the inferior half of the cornea divided by BL average thickness of the superior half of the cornea multiplied by 100), BEI-Max (defined as BL minimum thickness of the inferior half of the cornea divided by BL maximum thickness of the superior half of the cornea multiplied by 100), keratometric astigmatism (Ast-K) of patients with KC, and average keratometric (Avg-K) readings.

RESULTS

In patients with KC, BL vertical thickness maps disclosed localized relative inferior thinning of the BL. Inferior BL average thickness (normal = 15±2, KC = 12±3 μm), inferior BL minimum thickness (normal = 13±2, KC = 7±3 μm), BEI (normal = 91±7, KC = 48±14), and BEI-Max (normal = 75±8; KC = 40±13) all showed highly significant differences in KC compared with normal subjects (P< 0.001). Receiver operating characteristic (ROC) curve analysis showed excellent predictive accuracy for BEI and BEI-Max with 100% sensitivity and specificity (area under the curve [AUC] of 1) with cutoff values of 80 and 60, respectively. The AUC of inferior BL average thickness and minimum thickness were 0.87 and 0.96 with a sensitivity of 80% and 93%, respectively, and a specificity of 93% and 93%, respectively. Inferior BL average thickness, inferior BL minimum thickness, BEI, and BEI-Max correlated highly to Ast-K (R = -0.72, -0.82, -0.84, and -0.82, respectively; P< 0.001) and to Avg-K (R = -0.62, P< 0.001; R = -0.59, P = 0.001; R = -0.60, P< 0.001; and R = -0.59, P = 0.001, respectively).

CONCLUSIONS

Bowman's layer vertical topographic thickness maps of patients with KC disclose characteristic localized relative inferior thinning. Inferior BL average thickness, inferior BL minimum thickness, BEI, and BEI-Max are qualitative and quantitative indices for the diagnosis of KC that accurately correlate with the severity of KC. In our pilot study, BEI and BEI-Max showed excellent accuracy, sensitivity, and specificity in the diagnosis of KC.

Central and peripheral corneal thinning in keratoconus

PURPOSE

Recent data regarding the mid-peripheral portion of the removed corneal button in transplant surgery indicate histopathologically that keratoconus was present also in the peripheral portion of the button. The intent of this study was therefore to investigate if peripheral changes could also be detected clinically by measuring the central and peripheral corneal thickness of KC patients.

METHODS

Corneal pachymetry was measured with the Visante optical coherence tomography and Orbscan II. Of 52 subjects, 26 were KC subjects and 26 were age- and sex-matched control subjects.

RESULTS

Corneal thickness, in KC patients, was significantly reduced in all areas compared with corneal thickness among controls with both the Visante optical coherence tomography and Orbscan II.

CONCLUSION

The results of the present study have provided clinical evidence that KC is a disease affecting a wider area of the cornea. Although the KC cornea shows the greatest change in thickness in the ectatic region, this attenuation declines toward the periphery. The presence of peripheral thinning indicated that KC may be a "pancorneal" pathology and not limited to the ectatic portion.

Expression of SFRP Family Proteins in Human Keratoconus Corneas

We investigated the expression of the secreted frizzled-related proteins (SFRPs) in keratoconus (KC) and control corneas. KC buttons (∼8 mm diameter) (n = 15) and whole control corneas (n = 7) were fixed in 10% formalin or 2% paraformaldehyde and subsequently paraffin embedded and sectioned. Sections for histopathology were stained with hematoxylin and eosin, or Periodic Acid Schiff's reagent. A series of sections was also immunolabelled with SFRP 1 to 5 antibodies, visualised using immunofluorescence, and examined with a Zeiss LSM700 scanning laser confocal microscope. Semi-quantitative grading was used to compare SFRP immunostaining in KC and control corneas. Overall, KC corneas showed increased immunostaining for SFRP1 to 5, compared to controls. Corneal epithelium in all KC corneas displayed heterogeneous moderate to strong immunoreactivity for SFRP1 to 4, particularly in the basal epithelium adjacent to cone area. SFRP3 and 5 were localised to epithelial cell membranes in KC and control corneas, with increased SFRP3 cytoplasmic expression observed in KC. Strong stromal expression of SFRP5, including extracellular matrix, was seen in both KC and control corneas. In control corneas we observed differential expression of SFRP family proteins in the limbus compared to more central cornea. Taken together, our results support a role for SFRPs in maintaining a healthy cornea and in the pathogenesis of epithelial and anterior stromal disruption observed in KC.

Morphology of graft-host junction in cases with postkeratoplasty corneal ectasia

PURPOSE

We analyzed the central corneal and graft-host junction (GHJ) thickness profiles in cases with signs of corneal ectasia after penetrating keratoplasty for keratoconus.

METHODS

Anterior segment optical coherence tomography (ASOCT) was performed in cases with clinical or topographic signs of ectasia after complete suture removal. Corneal thickness was measured on the GHJ and at 1 mm on either side of the GHJ. Corneal thickness maps using Scheimpflug imaging were obtained.

RESULTS

Eight patients (11 eyes) with an average age of 52.55 ± 10.13 years were included. Mean age of the corneal grafts was 25.83 ± 12.37 years. Mean central corneal thickness was 577.45 ± 78.52 (range, 486-704) μm. Mean thickness 1 mm inside the GHJ, at the GHJ, and 1 mm outside the GHJ was 511.81 ± 66.15 (range, 380-600), 438.18 ± 86.35 (range, 260-550), and 465.45 ± 110.93 (range, 320-690) μm, respectively. Thinning of the graft, GHJ, or the host cornea was seen on ASOCT in all eyes. The central graft thickness was significantly higher compared with the graft thickness at and around the GHJ (P < 0.05 for all). The inferonasal quadrant was the thinnest in 7 eyes (63.63%).

CONCLUSIONS

Corneal thinning beyond the GHJ and subsequent ectasia can occur many years after initial keratoplasty in cases with keratoconus. Long-term follow-up of these cases may be desirable after corneal transplantation surgery. ASOCT is a useful tool for monitoring corneal thickness at and around the GHJ.

Quantified histopathology of the keratoconic cornea

PURPOSE

This study systematically investigated and quantified histopathological changes in a series of keratoconic (Kc) corneas using a physiologically formulated fixative to not further distort the already distorted diseased corneas.

METHODS

Twelve surgically removed Kc corneal buttons were immediately preserved and processed for light and transmission electron microscopy using an established corneal protocol. Measurements were taken from the central cone and peripheral regions of the host button. The sample size examined ranged in length from 390 to 2608 μm centrally and 439 to 2242 μm peripherally.

RESULTS

The average corneal thickness was 437 μm centrally and 559 μm peripherally. Epithelial thickness varied centrally from 14 to 92 μm and peripherally from 30 to 91 μm. A marked thickening of the epithelial basement membrane was noted in 58% of corneas. Centrally, anterior limiting lamina (ALL) was thinned or lost over 60% of the area examined, whereas peripheral cornea was also affected but to a lesser extent. Histopathologically, posterior cornea remained undisturbed by the disease. Anteriorly in the stroma, an increased number of cells and tissue debris were encountered, and some of these cells were clearly not keratocytes.

CONCLUSIONS

It is concluded that Kc pathology, at least initially, has a distinct anterior focus involving the epithelium, ALL, and anterior stroma. The epithelium had lost its cellular uniformity and was compromised by the loss or damage to the ALL. The activity of the hitherto unreported recruited stromal cells may be to break down and remove ALL and anterior stromal lamellae, leading to the overall thinning that accompanies this disease.

Longterm follow-up of penetrating keratoplasty for keratoconus

PURPOSE

This study aims to describe the current visual and refractive status of patients who underwent penetrating keratoplasty (PK) for keratoconus > 20 years ago and to report on the current status of their grafts.

METHODS

A total of 138 eyes in 103 patients were grafted for keratoconus between August 1968 and December 1985. Patients who had not undergone retransplantation were invited to attend a clinical examination. Forty-eight patients (with 61 grafts) accepted the invitation and were examined.

RESULTS

The average length of time since PK was 26.9 years (standard deviation [SD] 4.2 years, range 20.8-38.0 years, n = 61). The average graft age at examination was 82.1 years (SD 19.9 years, range 41-115 years). A total of 80% (49 of 61 grafts) of the examined eyes had a clear graft and 46% (28 of 61 eyes) had best spectacle-corrected visual acuity (BSCVA) > or = 0.5. The mean endothelial cell density per mm(2) was 894 (SD 4.6, range 470-1775). The mean central corneal thickness of the clear grafts was 0.565 mm (SD 0.048 mm).

CONCLUSIONS

Penetrating keratoplasty for keratoconus has a good longterm prognosis; half of the eyes examined in this study had BSCVA > or = 0.5 at > 20 years after surgery.

Recurrence of keratoconic pathology in penetrating keratoplasty buttons originally transplanted for keratoconus

PURPOSE

Study aimed to examine buttons removed from patients originally grafted for KC (group 1) for signs of recurrence at a cellular level and compare them with buttons removed from patients originally grafted for other conditions (group 2). The study further aimed to compare buttons from group 1 exhibiting high astigmatism (group 3) with the other buttons in the study (group 4).

METHODS

Together with clinical data, corneal buttons were collected at repeat penetrating keratoplasty and labeled immunohistochemically with a panel of antibodies to structural proteins to assist microanatomical interpretation. Image analysis of montaged images of many individual sections was performed using custom software. The resulting data were analyzed statistically for significant differences between groups 1/2 and 3/4.

RESULTS

Little evidence of KC recurrence could be found despite statistically significant differences between groups 1/2 in corneal thinning at both graft-host junction (GHJ) (P = 0.035) and within the graft (P = 0.001), epithelial thickening at the GHJ only (P < 0.001), high astigmatism (P = 0.028), and history of high intraocular pressure (P = 0.032) or rejection (P = 0.002) and between groups 3/4 in corneal thinning at both GHJ (P = 0.002) and within the graft (P = 0.003), epithelial thickening at the GHJ only (P = 0.003), and high astigmatism (P < 0.001).

CONCLUSION

This study has highlighted the rarity of recurrence of KC in transplanted donor corneas and the corresponding difficulty in detecting early signs of the disease.

Long-term keratometric changes after penetrating keratoplasty for keratoconus and Fuchs Endothelial dystrophy

PURPOSE

To compare long-term keratometric changes after penetrating keratoplasty (PK) for keratoconus and Fuchs endothelial dystrophy.

DESIGN

Retrospective, comparative case series.

METHODS

We retrospectively analyzed 168 corneas after PK for keratoconus (85 eyes of 63 subjects) and Fuchs dystrophy (83 eyes of 60 subjects). Patients were examined after final suture removal at 12 months after PK to 30 years after surgery. Operations were performed by one surgeon (W.M.B.) using the same suturing technique in all cases. Eyes were excluded from further analysis after regrafting or after relaxing incisions. Mean keratometric corneal power and astigmatism were measured by manual keratometry. Data were assessed by using generalized estimating equation models to determine change over time.

RESULTS

Mean keratometric corneal power and astigmatism increased through 30 years after PK for keratoconus (P < .001 and P < .001), but did not change through 20 years after PK for Fuchs dystrophy (P = .55 and P = .55) The change in keratometric corneal power and astigmatism after PK in keratoconus patients only differed from the change in Fuchs dystrophy patients 10 or more years after PK (P = .002 and P = .003).

CONCLUSIONS

Corneal curvature and regular astigmatism increase progressively after PK for keratoconus, but remain stable after PK for Fuchs dystrophy. Our data suggest that keratometric instability after PK for keratoconus is attributable to delayed, progressive ectasia in the host corneal rim.

Recurrent ectasia in corneal grafts and outcomes of repeat keratoplasty for keratoconus

AIM

To analyse cases of recurrent ectasia in donor corneas after penetrating keratoplasty (PK) for keratoconus.

METHODS

Data on 25 patients (36 eyes) with recurrent ectasia were retrospectively analysed in this study. The main outcome measures were time to development of recurrent ectasia after first PK for keratoconus, change in keratometric sphere and astigmatism between final suture removal and development of recurrent ectasia, status of regrafts for recurrent ectasia, and histopathology of grafts excised for recurrent ectasia.

RESULTS

The age at first PK was 32.6 (SD 8.5) years, and ectasia developed 21.9 (7.0) years after PK. The mean keratometric sphere and cylinder increased by 4.2 D and 3.0 D, respectively, between final suture removal and diagnosis of recurrent ectasia. Ectasia was often preceded by thinning without bulging of the recipient stroma at the graft-host junction. Fifteen eyes (13 patients) were regrafted for recurrent ectasia, and histopathology of the excised grafts showed changes characteristic of keratoconus in the donor tissue in all cases. Two regrafts (two eyes of one patient) developed ectasia again, with one eye requiring a third PK to improve vision.

CONCLUSIONS

Recurrent ectasia was diagnosed on average two decades after PK. Ectatic changes were often bilateral and occasionally recurred after regrafting, suggesting that host cellular and/or biochemical factors may be responsible. Repeat PK for recurrent ectasia is successful in the intermediate term.

Late corneal hydrops after penetrating keratoplasty for keratoconus

PURPOSE

To report 2 cases of corneal hydrops occurring in eyes with previously healthy corneal grafts.

METHODS

Retrospective case series. A report of 2 presenting cases. Both patients underwent a full ophthalmic clinical examination and anterior segment optical coherence tomography (OCT).

RESULTS

Two patients with longstanding corneal grafts for keratoconus presented with an acute painful red eye and reduced vision. They were found to have acute hydrops with breaks in and detachments of Descemet membrane.

CONCLUSIONS

Keratoconic patients with longstanding corneal grafts who present acutely with corneal edema must be carefully examined not only for signs of graft rejection or failure but also for acute hydrops. Important differentiating signs may be a Descemet break or detachment and the presence of stromal edema across the donor-host corneal interface.

Recurrence of Keratoconus in Two Corneal Grafts After Penetrating Keratoplasty

PURPOSE

To report the recurrence of postkeratoplasty keratoconus in 2 corneal grafts harvested from the same donor.

DESIGN

Interventional case reports.

METHODS

A 21-year-old-man with advanced keratoconus in his right eye and a 28-year-old-woman with corneal leucoma in her right eye underwent penetrating keratoplasty with 2 grafts coming from the same donor. Approximately 1.5 years after grafting, corneal irregularity and astigmatism caused visual acuities of the patients to decrease to counting fingers. Clinical findings and corneal topography suggested the recurrence of keratoconus. A repeat keratoplasty was performed in both patients.

RESULTS

Histopathology of the excised corneal grafts was consistent with keratoconus and confirmed the preoperative diagnosis.

CONCLUSIONS

Recurrence of keratoconus in a patient who had no preexisting keratoconus and in 2 corneal grafts coming from the same donor suggested transmission of the disorder from the donor instead of true recurrence.

Histopathological and immunohistochemical studies of lenticules after epikeratoplasty for keratoconus

AIMS

To examine histopathological and immunohistochemical changes in lenticules and host of corneal buttons from patients who previously underwent epikeratoplasty for keratoconus.

METHODS

12 penetrating keratoplasty specimens from patients with keratoconus who had previously undergone epikeratoplasty, eight keratoconus, and seven normal corneas were examined. Immunostaining for Sp1, alpha1-proteinase inhibitor (alpha1-PI), and alpha2-macroglobulin (alpha2M) were performed.

RESULTS

In nine of the 12 lenticules, the keratoconus-like disruptions were found in Bowman's layer. Peripheral and posterior keratocyte repopulation of the lenticules was observed in all cases. Keratocyte repopulation in the anterior and mid-stromal regions of the lenticules appeared related to the time since epikeratoplasty. Sp1 nuclear staining of the basal and wing epithelial cells was more intense in lenticules and keratoconus corneas than in normal corneas. Lenticular, host, and keratoconus keratocytes showed positive Sp1 staining, whereas staining was absent in normal corneas. Compared to normal corneas, alpha1-PI and alpha2M immunostaining was lower in the lenticules, host, and keratoconus specimens.

CONCLUSIONS

The epithelial cells and keratocytes repopulated in the lenticules retain keratoconus-like biochemical abnormalities such as upregulation of Sp1 and downregulation of alpha1-PI and alpha2M. The authors speculate that both keratocytes and the corneal epithelium may participate in the development of keratoconus.

PAX6 expression identifies progenitor cells for corneal keratocytes

Keratocytes of the corneal stroma produce a transparent extracellular matrix required for vision. During wound-healing and in vitro, keratocytes proliferate, becoming fibroblastic, and lose biosynthesis of unique corneal matrix components. This study sought identification of cells in the corneal stroma capable of assuming a keratocyte phenotype after extensive proliferation. About 3% of freshly isolated bovine stromal cells exhibited clonal growth. In low-mitogen media, selected clonal cultures displayed dendritic morphology and expressed high levels of keratan sulfate, aldehyde dehydrogenase 3A1, and keratocan, molecular markers of keratocyte phenotype. In protein-free media, both primary keratocytes and selected clonal cells aggregated to form attachment-independent spheroids expressing elevated levels of those marker molecules. The selected clonal cells exhibited normal karyotype and underwent replicative senescence after 65-70 population doublings; however, they continued expression of keratocyte phenotypic markers throughout their replicative life span. The progenitor cells expressed elevated mRNA for several genes characteristic of stem cells and also for genes expressed during ocular development PAX6, Six2, and Six3. PAX6 protein was detected in the cultured progenitor cells and a small number of stromal cells in intact tissue but was absent in cultured keratocytes and fibroblasts. Cytometry demonstrated PAX6 protein in 4% of freshly isolated stromal cells. These results demonstrate the presence of a previously unrecognized population of PAX6-positive cells in adult corneal stroma that maintain the potential to assume a keratocyte phenotype even after extensive replication. The presence of such progenitor cells has implications for corneal biology and for cell-based therapies targeting corneal scarring.

Morphological changes in keratoconus: pathology or pathogenesis

Keratoconus was first discriminated from other corneal ectatic diseases in 1854. Since that time the morphological characteristics of keratoconic progression have been invaluable in the diagnosis of the condition. The key clinical features used to identify keratoconus have remained essentially the same since the introduction of the slit-lamp biomicroscope. Only relatively recently has the development of computerized corneal topography revolutionized the diagnosis of early keratoconus. Analysis of peer-reviewed literature databases revealed a steady chronological increase in pathological research into the progress of keratoconus. This overview describes the recent advances in our understanding of keratoconic pathology and highlights the interactions within the cornea that may be important in the pathogenesis of this condition.

Late-Stage Progressive Corneal Astigmatism After Penetrating Keratoplasty for Keratoconus

PURPOSE

Progressive corneal astigmatism occurring at least 10 years after penetrating keratoplasty for keratoconus is a late-phase complication of surgery. This report characterizes this condition in a series of patients from three corneal referral centers in the United States.

METHODS

Charts were retrospectively reviewed which met the following criteria: penetrating keratoplasty performed for keratoconus at least 10 years ago, keratometry or simulated keratometry from topography as well as manifest refraction recorded at least 6 months after the last suture removal ("baseline"), and an increase in corneal astigmatism of at least three D over baseline recorded at least 5 years later. Patients who had any other corneal or intraocular surgery performed were excluded.

RESULTS

Data from 15 patients (11 males and 4 females) who had penetrating keratoplasties performed by 8 different surgeons are included in this descriptive series. Postoperative follow-up averaged 17.27 years (range 11-24 years). The average donor button size was 7.83 mm (range 7.25-8.5 mm). Baseline corneal astigmatism was obtained an average of 5.2 years after penetrating keratoplasty (range 1.5-16 years) and was on average 3.57 +/- 1.8 D (10 with-the-rule [WTR], 3 against-the-rule [ATR], 2 oblique). Corneal astigmatism significantly increased to an average of 11.23 +/- 3.56 D (range 8.00-19.37 D, P < 0.0001) and most astigmatism was regular and WTR (9 WTR, 3 ATR, 3 oblique) 15.3 years (range 10-22 years) after surgery. Inferior steepening on topography was often noted, even those with oblique and ATR axes.

CONCLUSIONS

High, late-stage, regular astigmatism after penetrating keratoplasty for keratoconus is described in a series of patients occurring at least 10 years after surgery. Possible mechanisms of this progressive astigmatism are recurrence of keratoconus in the graft, progressive corneal thinning of the host cornea, or progressive misalignment of the graft-host interface over time.