Rotational stability of two different piggyback toric intraocular lenses for correction of high post-keratoplasty pseudophakic ametropia.

We present the case of a 65-year-old man with bilateral keratoconus and history of bilateral penetrating keratoplasty (PK) who developed gradual visual decline in the left eye due to cataract formation. Following successful left eye cataract surgery and monofocal, non-toric intraocular lens (IOL) in-the-bag implantation, the patient experienced persistently low uncorrected distance visual acuity (UDVA) due to high residual refractive error and intolerance to contact lenses. A supplementary toric IOL was placed in the ciliary sulcus, but subsequent rotational instability of the lens required repeated realignment. Despite two attempts at IOL repositioning, the rotational instability persisted, necessitating the replacement of the original Sulcoflex IOL with a toric, implantable Collamer lens. Following the implantation of the toric ICL, the patient achieved excellent UDVA with no adverse events over a 4-year follow-up period. This case highlights the potential rotational instability associated with toric piggyback IOLs in keratoconic, post-PK, pseudophakic eyes and the special considerations on choosing the type of piggyback lens in these eyes.

Subfoveal choroidal thickness increases after excimer laser-assisted penetrating keratoplasty but not after excimer laser-assisted deep anterior lamellar keratoplasty.

To evaluate the impact of excimer laser-assisted deep anterior lamellar keratoplasty (Exc-DALK) and excimer laser-assisted penetrating keratoplasty (Exc-PKP) on subfoveal choroidal thickness (SFCT) in eyes with advanced keratoconus. A retrospective comparative clinical study, which compares the outcomes of 24 eyes treated with Exc-DALK (G1) against matched group of 43 eyes treated with Exc-PKP (G2) at both 2 months (T1) and 2 years (T2) postoperatively. Main outcomes included best-corrected visual acuity (BCVA), central macular thickness (CMT), and SFCT. Preoperatively, there were no significant differences between both groups regarding BCVA, CMT or SFCT (p > 0.05). There were no significant differences between both groups regarding BCVA at both follow-ups (p > 0.05). There were no significant differences between both groups regarding CMT at both follow-ups (p > 0.05). SFCT was higher in G2 than G1 at both follow-ups (p < 0.01). Compared to preoperative SFCT, there were no significant changes in SFCT in G1 at both follow-ups (p > 0.05). In G2, SFCT increased significantly at T1 (p < 0.01) and did not differ significantly at T2 (p = 0.17). SFCT increased significantly after Exc-PKP but not after Exc-DALK, which might indicate that Exc-DALK affects the choroid less and thus could represent a less traumatic approach to ocular tissue than Exc-PKP.

A new technique to implant intracorneal ring-segments from the perilimbal region: one-year prospective pilot study report.

BACKGROUND: Recently a new surgical technique for intracorneal ring-segments (ICRS) assisted by femtosecond laser (FSL) called ByLimB was developed, involving the creation of the incision from a paralimbic region. This study aims to evaluate the safety and efficacy of the ByLimb technique following one year of follow-up. METHODS: A prospective, single-center study was conducted at the Zaldivar Institute in Buenos Aires, Argentina. Keratoconus patients with indication for ICRS-FSL assisted procedure, operated with the ByLimb technique were included. By using the ByLimb technique, the ICRS are placed without affecting the tunnel's roof, and the end of the ICRS is always away from the incision area. Visual acuity, topographic astigmatism, and the occurrence of complications were evaluated. Safety index was the main outcome and efficacy indes was a complimentary outcome. RESULTS: A total of 17 eyes completed the 12-month follow-up period. The safety index was 1.10 (mean postoperative corrected distance visual acuity (CDVA) in decimal: 0.76/preoperative CDVA: 0.69), while the efficacy index was 0.89 (mean postoperative uncorrected distance visual acuity UDVA in decimal: 0.62/preoperative CDVA: 0.69). Mean preoperative astigmatism was 5.3 ± 2.3, decreasing twelve months after surgery at 2.1 ± 1.2 (p < 0.001). No eye loss lines of vision and no intraoperative complications were observed. During the first month after surgery, an improper positioning of the ICRS based on topographic assessment was detected in five cases. A second procedure was performed, which consisted of opening the incision and introducing a Sinsky hook, through which the ICRS was mobilized and placed in its correct position. No incisional alterations, signs of infection, anterior segment anomalies, or fundus alterations were observed. CONCLUSION: FSL-assisted ICRS implantation through the perilimbal region has demonstrated an adequate safety index one year post-surgery. Additionally, this technique has facilitated accurate realignment of ICRS during secondary surgical interventions within one-month post-surgery. While the current findings are promising, continued follow-up of these cases is warranted.

Management of Acute Corneal Hydrops Using Compression Sutures and Intracameral Air Injection.

BACKGROUND Acute corneal hydrops, a rare complication of keratoconus, is characterized by sudden onset of corneal stroma edema. It typically manifests as an acute decrease in visual acuity, accompanied by pain and photophobia. Prompt recognition and interventions are critical for effective resolution of hydrops and prevention of corneal vascularization. Herein, we present a case of a patient with keratoconus who developed corneal hydrops, successfully managed using full-thickness compression sutures and intracameral air injection. CASE REPORT A woman in her early 30s, with a history of keratoconus, presented with symptoms of acute hydrops in her left eye. On presentation, best corrected visual acuity was hand motion. Slit-lamp examination revealed marked corneal edema with multiple stromal clefts. The decision was made to perform full-thickness compression sutures combined with intracameral air injection to expedite edema resolution and prevent neovascularization. Three full-thickness sutures were placed across Descemet membrane breaks, and an air bubble was left, filling 50% of the anterior chamber. At 3-month follow-up, a clear, compact cornea was noted, with no evidence of vascularization. The patient was scheduled for penetrating keratoplasty for visual rehabilitation. CONCLUSIONS The combination of full-thickness compression sutures and intracameral air seems to be an effective and safe method for preventing corneal angiogenesis following hydrops. As corneal scaring is often an inevitable complication of acute corneal hydrops, keratoplasty is necessary for improving visual acuity. Hence, the prevention of corneal vascularization should be the major aim in the management of corneal hydrops to ensure successful keratoplasty.

Effect of Corneal Allogenic Intrastromal Ring Segment (CAIRS) Implantation Surgery in Patients With Keratoconus According to Prior Corneal Cross-linking Status.

PURPOSE: To compare the effects of corneal allogenic intrastromal ring segment (CAIRS) implantation on topographical measurements and visual outcomes of patients with keratoconus with and without corneal cross-linking (CXL) prior to the time of implantation. METHODS: Sixty-seven eyes with corneal allograft intrastromal ring segment implantation (KeraNatural; Lions VisionGift) due to advanced keratoconus were included in the study. Thirty-seven eyes had no CXL and 30 eyes had had CXL before being referred to the authors. The changes in spherical equivalent (SE), uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), steep keratometry (K1), flat keratometry (K2), mean keratometry (Kmean), maximum keratometry (Kmax), and thinnest pachymetry were retrospectively analyzed 6 months after the implantation. RESULTS: The median age was 29 years in the CXL group and 24.0 years in the non-CXL group (P > .05), respectively. All topographical and visual parameters before implantation were similar in both groups (P > .05 for all parameters). At 6 months, CDVA, K1, and Kmean showed higher improvement in the non-CXL group than the CXL group (P = .030, .018, and .039, respectively). CONCLUSIONS: CAIRS surgery has a flattening effect on both the corneas with and without CXL. The cornea with prior CXL treatment had less flattening effect due to the stiffening effect of prior CXL. [J Refract Surg. 2024;40(6):e392-e397.].

Risk factors for corneal graft rejection after penetrating keratoplasty for keratoconus.

PURPOSE: To evaluate the association between donor-related factors and the risk of rejection in patients undergoing penetrating keratoplasty (PKP) for keratoconus. METHODS: A retrospective review was performed of keratoconus patients with no corneal neovascularization who underwent PKP from November 2014 to December 2016 and completed at least two years of follow-up. Preoperative, donor, operative, and postoperative data were collected and analyzed to identify factors leading to corneal graft rejection. RESULTS: A total of 201 eyes (of 201 patients) that underwent PKP for keratoconus were included. Of these, 22.9% (95% CI 17.6-29.2%) had an episode of graft rejection. The overall graft survival rate was 98.5%. Receipts with a history of corneal transplant in the fellow eye (IRR 1.69, 95% CI 1.01, 2.80; p = 0.044) and those with postoperative stromal neovascularization (IRR 2.51, 95% CI 1.49, 4.21; p = 0.001) had a significantly higher incidence of rejection than those without these features. In univariate analysis, death-to-surgery time and death-to-excision time (DET) showed a weak association with graft rejection (p 0.05 and 0.08 respectively); However, in the multivariable analysis, this significance was lost. Grafts with a death-to-excision time (DET) greater than 8 h had a 0.53X lower risk of rejection compared with grafts with DET within 8 h or less (p = 0.05). Rejection was higher in patients receiving grafts with a preservation time within 7 days or less compared with preservation time greater than 7 days (30.6% vs. 21.2%, respectively, p = 0.291). CONCLUSION: In the multivariable analysis, none of the donor-related factors were significantly associated with graft rejection; however, short death-to-surgery time may be associated with rejection after PKP. Recipients with a history of PKP in the fellow eye and those who developed corneal neovascularization were also at increased risk of developing rejection after keratoplasty.

[Comparative analysis of clinical and functional parameters in patients with stable stage II-III keratoconus after implantation of corneal segments and fitting of scleral rigid contact lenses]. / Sravnitel'nyi analiz kliniko-funktsional'nykh pokazatelei u patsientov so stabil'nym keratokonusom II­III stadii posle implantatsii rogovichnykh segmentov i podbora skleral'nykh zhestkikh kontaktnykh linz.

The modern treatment strategy for keratoconus (KC) involves sequential application of medical technologies aimed at stabilizing pathological changes in the cornea and restoring visual acuity. PURPOSE: This study compares the effect of implantation of intrastromal corneal ring segment (ICRS) and fitting of individual scleral rigid contact lenses (RCLs) on visual functions in patients with stage II-III KC after previously performed corneal collagen cross-linking. MATERIAL AND METHODS: The Helmholtz National Medical Research Center of Eye Diseases examined and treated 34 patients (69 eyes) aged 18 to 33 years with stage II-III KC. The study included patients who had previously undergone standard corneal collagen cross-linking. Depending on the type of optical correction, the patients were divided into two groups: patients in group 1 underwent ICRS implantation using a femtosecond laser; patients in group 2 were fitted with individual scleral RCLs. RESULTS: Improvement in clinical and functional parameters was observed in both groups. A higher clinical and functional result was achieved in group 2. CONCLUSION: For patients with stable stage II-III KC, it is advisable to recommend fitting of individual scleral RCLs for visual rehabilitation.

Combined topography-guided photorefractive keratectomy and corneal collagen crosslinking.

PURPOSE: This study aimed to report the long-term results of combined topography-guided photorefractive keratectomy (PRK) and accelerated corneal collagen cross-linking (CXL) for keratoconus using the Zeiss refractive coordinated system. METHODS: A prospective interventional study was conducted in a tertiary eye care hospital in South India. Patients with mild-to-moderate progressive keratoconus and corneal pachymetry greater than 450 µm were included. They underwent customized topography-guided PRK followed by CXL. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and keratometry readings and complications were evaluated at 1, 3, 6, 12, and 24 months postoperatively. RESULTS: Thirty patients (30 eyes) were included in the study. All study parameters showed a statistically significant improvement postoperatively over baseline values. At 24 months, the mean UDVA improved from 0.8 ± 0.180 logarithm of the minimum angle of resolution (logMAR) to 0.38 ± 0.118 logMAR ( P -value <0.001) and CDVA improved from 0.467 ± 0.142 logMAR to 0.227 ± 0.078 logMAR ( P -value <0.001). The mean flat, steep, and maximum keratometry values were significantly reduced by 2.133, 3, and 4.54 diopters, respectively, at the last follow-up examination ( P -value <0.001). CONCLUSION: The combined topography-guided PRK and accelerated CXL procedure seem to be a promising treatment alternative for early keratoconus. This is the first such study on the Zeiss refractive coordinated system. However, further studies with a larger study population and longer follow-up periods are required to draw final conclusions about the benefits of this procedure in keratoconus.

[Alternative methods of surgical treatment of keratoconus]. / Al'ternativnye metody khirurgicheskogo lecheniya keratokonusa.

The introduction of early diagnostic methods for keratoconus into clinical practice has become the basis for the development of surgical treatment techniques for this pathology, such as corneal collagen crosslinking and interlamellar keratoplasty with implantation of intrastromal segments. The article analyzes the results of research by Russian and foreign specialists in these areas and presents the data on the combination of SMILE surgery and corneal crosslinking, the Rome protocol of corneal crosslinking, modifications of interlamellar keratoplasty, the use of femtosecond laser technologies, and some pilot studies. Modern requirements for ophthalmological care require a personalized approach to each patient, and therefore the surgeon should have a wide range of surgical methods of treatment applicable to different patient cohorts. The described methods of treatment, according to the authors, are the most promising.

[Effect of keratoplasty on the quality of life of keratoconus patients]. / Effet de la kératoplastie sur la qualité de vie des patients atteints de kératocône.

Corneal deformations caused by keratoconus produce high levels of optical aberration (OA). Despite appropriate optical correction, these alter the quality of vision and diminish the patient's quality of life, especially since the affected population is predominantly young and of working age. When thinning is too severe or corneal transparency too impaired, a corneal transplant may be considered. In this study, we compare the quality of life of patients with keratoconus in the early (stages 1 and 2) or advanced (stages 3 and 4) stages of the Krumeich classification, as well as patients who have had keratoconus treated by keratoplasty. Quality of life was assessed using the NEI-VFQ 25 questionnaire, the most widely used for keratoconus. An aberrometric examination (OQAS®; HD Analyser, Visiometrics, Terrassa, Spain) was also performed to assess patients' quality of vision. Our results show that keratoplasty provides an improvement in quality of life compared with advanced-stage keratoconus in the areas of distance (p=0.0083) and near vision (p=0.029) activities. This improvement also applies to Best-Corrected Visual Acuity (BCVA) (p=0.032) and transparency (OSI) (p=0.049). Our study shows that keratoplasty improves corneal transparency, and it is interesting to note that it improves patients' quality of life over the long term.

Evaluation of dynamic corneal response parameters and the biomechanical E-staging after Intacs® SK implantation in keratoconus.

PURPOSE: This retrospective longitudinal study evaluated the biomechanical E-staging in KC corneas before and after intracorneal ring segment (ICRS) implantation (Intacs® SK, Addition Technology, Illinois, United States). METHODS: Biomechanical E-staging for ectatic corneal diseases was applied retrospectively on 49 KC corneas of 41 patients who underwent ICRS implantation. The main outcome parameters included the Corvis Biomechanical Factor (CBiF, the linearized Corvis Biomechanical Index and the biomechanical parameters included), the resulting biomechanical E-staging, the stress-strain index, thinnest corneal thickness (TCT), maximal anterior keratometry (Kmax), and the anterior radius of curvature (ARC). They were evaluated at 1.9 ± 1.1 months preoperatively and postoperatively after 2.8 ± 0.7, 5.8 ± 1.0, and 10.6 ± 2.3 months. RESULTS: The CBiF decreased (4.9 ± 0.5 | 4.7 ± 0.5, P = 0.0013), and the E-staging increased significantly (2.8 ± 0.8 | 3.1 ± 0.9, P = 0.0012, paired t-test) from preoperatively to the first postoperative follow-up. The difference remained significant after 6 months; however, there was no more difference after 11 months. TCT was stable, whereas Kmax and ARC significantly decreased after ICRS implantation (TCT: 464 ± 49, 470 ± 51, 467 ± 38, 461 ± 48; Kmax: 56.3 ± 4.5, 54.7 ± 4.5, 54.2 ± 4.8, 54.1 ± 4.3; ARC: 51.5 ± 3.4, 48.3 ± 3.8, 48.6 ± 3.0, 48.6 ± 3.2 preoperatively and 3, 6, and 11 months postoperatively, respectively). Besides Kmax and ARC, Ambrósio's relational thickness to the horizontal profile (ARTh) was the only parameter that was significantly lower than preoperatively at any follow-up (P ≤ 0.0024, Wilcoxon matched-pairs test). CONCLUSION: Intacs® SK implantation results in an increasing biomechanical E-staging in the first postoperative months with stabilization near preoperative values after 1 year. Significantly lower ARTh values at any follow-up document the ICRS effect and contribute to a slightly higher postoperative biomechanical E-staging value.

Functional Approach to IOL Selection in Eyes With Combined Cataract and Keratoconus With an Option for Refractive Lens Exchange.

PURPOSE: To evaluate spherical intraocular lens (IOL) implantation for cataracts in keratoconic eyes followed by optional refractive toric lens exchange to improve uncorrected visual acuity. METHODS: This retrospective study evaluated cataract surgery outcomes in keratoconic eyes. Eyes treated with a spherical IOL targeted for -2.00 diopters (D) either achieved acceptable manifest refraction and desired exchange with a toric IOL (Group 1); achieved satisfactory manifest refraction and chose to use spectacles or contact lenses (Group 2); or did not achieve acceptable refraction and used contact lenses (Group 3). Group 4 had single-stage toric IOL implantation with plano target. Corrected and uncorrected distance visual acuity (CDVA and UDVA) and keratometry were analyzed. RESULTS: Groups 1 to 4 had 18, 23, 18, and 26 eyes, respectively. A staged toric exchange resulted in significantly better (P = .02) UDVA (mean: 0.15 logMAR; 20/25 Snellen) than initial toric IOL implantation (0.24 logMAR; 20/30 Snellen). All toric IOL exchange eyes achieved 20/30 or better CDVA and 94% had 20/40 or better UDVA. Mean manifest cylinder significantly decreased from 3.39 D before lens exchange to 1.10 D postoperatively. CONCLUSIONS: Initial implantation of a spherical IOL in keratoconic eyes allows basing toric calculations on the manifest refraction, which may be more reliable than keratometry measurements in keratoconic eyes. UDVA after staged toric IOL exchange was significantly better than after initial toric IOL implantation. Importantly, by staging use of toric lenses, the authors avoided cases where patients required a rigid contact lens after a toric IOL was implanted. [J Refract Surg. 2024;40(4):e207-e217.].

Comparison of keratoplasty outcomes at the scar versus edema stages of keratoconus.

PURPOSE: To assess the outcomes of deep anterior lamellar keratoplasty or penetrating keratoplasty at the scar and the edema stages. METHODS: Forty-five patients (45 eyes) with keratoconus scar stage (scar group, n=26; penetrating keratoplasty a subgroup, n=7; deep anterior lamellar keratoplasty b subgroup, n=19) and keratoconus edema stage (edema group, n=19; penetrating keratoplasty c subgroup, n=12; deep anterior lamellar keratoplasty d group, n=7) who received penetrating keratoplasty or deep anterior lamellar keratoplasty from 2000 to 2022 were retrospectively studied. At 1, 6, and 12 months after surgery, the best-corrected visual acuity, astigmatism, spherical equivalent, corneal endothelial cell density, and complications were analyzed. RESULTS: The best-corrected visual acuity and average corneal endothelial cell loss rate were not significantly different between the scar and edema groups (p>0.05). At 6 and 12 months after surgery, the astigmatism and spherical equivalent in the scar group were significantly lower than those in the edema group (p<0.05). The spherical equivalent of the deep anterior lamellar keratoplasty b subgroup was lower than that of the penetrating keratoplasty a subgroup in the scar group 6 months after surgery (p<0.05). In the edema group, there was no significant difference in spherical equivalent between subgroups (p>0.05). There were no significant differences in best-corrected visual acuity and astigmatism between subgroups within the two groups (p>0.05). In comparison to the scar group, the edema group experienced more complications. According to a survival analysis, there was no statistically significant difference between the scar group and the edema group regarding the progression of vision. CONCLUSIONS: In terms of the outcomes and prognosis for vision after keratoplasty with edema stage and scar stage, deep anterior lamellar keratoplasty may be as effective as penetrating keratoplasty.

Deep anterior lamellar keratoplasty and penetrating keratoplasty in macular corneal dystrophy: comparison of visual and topographic outcomes and complications.

PURPOSES: This study aims to assess and compare the postoperative visual and topographic outcomes, complications, and graft survival rates following deep anterior lamellar keratoplasty and penetrating keratoplasty in patients with macular corneal dystrophy. METHODS: In this study we enrolled 59 patients (23 male; and 36 female) with macular corneal dystrophy comprising 81 eyes. Out of these, 64 eyes underwent penetrating keratoplasty, while 17 eyes underwent deep anterior lamellar keratoplasty. The two groups were analyzed and compared based on best-corrected visual acuity, corneal tomography parameters, pachymetry, complication rates, and graft survival rates. RESULTS: After 12 months, 70.6% of the patients who underwent deep anterior lamellar keratoplasty (DALK) and 75% of those who had penetrating keratoplasty (PK) achieved a best-corrected visual acuity of 20/40 or better (p=0.712). Following surgery, DALK group showed lower front Kmean (p=0.037), and Q values (p<0.01) compared to the PK group. Postoperative interface opacity was observed in seven eyes (41.2%) in the DALK group. Other topography values and other complications (graft rejection, graft failure, cataract, glaucoma, microbial keratitis, optic atrophy) did not show significant differences between the two groups. The need for regrafting was 9.4% and 11.8% in the PK and DALK groups, respectively (p=0.769). Graft survival rates were 87.5% and 88.2% for PK and DALK; respectively (p=0.88 by Log-rank test). CONCLUSION: Both PK and DALK are equally effective in treating macular corneal dystrophy, showing similar visual, topographic, and survival outcomes. Although interface opacity occurs more frequently after DALK the visual results were comparable in both groups. Therefore, DALK emerges as a viable surgical choice for patients with macular corneal dystrophy without Descemet membrane involvement is absent.

Management of corneal melting after collagen cross-linking for keratoconus: a case report and a review of the literature.

PURPOSE: We describe the management of a case of severe corneal melting after corneal cross-linking (CXL) treated with a staged approach using a conjunctival flap followed by deep anterior lamellar keratoplasty (DALK). METHODS: A 12-year-old male developed severe corneal melting with pending perforation after an accelerated epithelium-off CXL protocol. We initially treated the patient with a conjunctival flap to prevent perforation. Three months later, we performed DALK to restore vision. RESULTS: Conjunctival flap surgery allowed us to avoid corneal perforation and penetrating keratoplasty (PK) à chaud. Once the inflammation had resolved, we recessed the conjunctiva and performed DALK for optical purposes. Twelve months later, the graft was clear and the corrected visual acuity was 20/25 (Snellen). No complications occurred after surgery. CONCLUSIONS: Although CXL is considered a safe procedure, in rare cases it can lead to serious complications, such as corneal haze, infectious and non-infectious keratitis, stromal melting and perforation. Corneal melting and perforation are usually managed by emergency PK. Herein we suggest a staged approach involving an emergency conjunctival flap followed by DALK at a later time that allowed us to avoid PK à chaud.

Congenital stromal corneal dystrophy in a Spanish family: Clinical, genetic and histological analysis.

PURPOSE: To present the clinical, genetic, and histopathological features of the ninth family affected by congenital stromal corneal dystrophy (CSCD) to date. METHODS: Twelve cases of a Spanish family affected by CSCD were analyzed regarding history, visual acuity (VA, decimal scale), an ophthalmologic exam and specular microscopy. Five eyes were treated by deep anterior lamellar keratoplasty (DALK), and thirteen eyes by penetrating keratoplasty (PK). In the two last generations, a genetic study was performed. RESULTS: Most of the patients affected were born with opaque corneas except for three, whose corneas were clear at birth. Biomicroscopy showed a whitish diffuse stromal opacity with an unaltered epithelium, causing poor VA (from hand motions to 0.4). Patients treated with PK presented mean postoperative VA of 0.19±0.20 over a follow-up time of 235.3±101.4months with 38% recurrences. Patients who underwent DALK experienced VA improvement to 0.17±0.11 over a follow-up time of 10.8±2.6months without signs of recurrence. In the latter, the big bubble technique was not achieved, so a manual technique was performed. The genetic study showed heterozygosis for a 1-bp deletion at nucleotide 962 in exon 8 of the decorin gene. CONCLUSIONS: CSCD is a rare entity, which should be treated by DALK whenever possible, obtaining better results than PK. Close monitoring of children of affected individuals is important, because CSCD can progress during the early years of life.

Corneal biomechanics and diagnostics: a review.

PURPOSE: Corneal biomechanics is an emerging field and the interest into physical and biological interrelations in the anterior part of the eye has significantly increased during the past years. There are many factors that determine corneal biomechanics such as hormonal fluctuations, hydration and environmental factors. Other factors that can affect the corneas are the age, the intraocular pressure and the central corneal thickness. The purpose of this review is to evaluate the factors affecting corneal biomechanics and the recent advancements in non-destructive, in vivo measurement techniques for early detection and improved management of corneal diseases. METHODS: Until recently, corneal biomechanics could not be directly assessed in humans and were instead inferred from geometrical cornea analysis and ex vivo biomechanical testing. The current research has made strides in studying and creating non-destructive and contactless techniques to measure the biomechanical properties of the cornea in vivo. RESULTS: Research has indicated that altered corneal biomechanics contribute to diseases such as keratoconus and glaucoma. The identification of pathological corneas through the new measurement techniques is imperative for preventing postoperative complications. CONCLUSIONS: Identification of pathological corneas is crucial for the prevention of postoperative complications. Therefore, a better understanding of corneal biomechanics will lead to earlier diagnosis of ectatic disorders, improve current refractive surgeries and allow for a better postoperative treatment.

Severe ulcerative keratopathy following implantation of an acellular porcine corneal stromal lenticule in a patient with keratoconus.

PURPOSE: To report a case of ulcerative keratopathy following implantation of acellular porcine corneal stroma (APCS) in a patient with keratoconus (KC). METHODS: A 58 year-old patient initially presented with an ulcerative keratopathy in the left eye. Previously, several corneal procedures (including radial keratotomy, laser-in-situ keratomileusis, crosslinking) were performed for KC. Eight months ago, an APCS lenticule (Xenia corneal implant, Gebauer Medizintechnik GmbH, Neuhausen, Germany) was implanted into a stromal pocket because of progressive keratectasia. Visual acuity was hand movement. Anterior segment optical coherence tomography showed a space between the APCS lenticule and the host stroma. Excimer laser-assisted penetrating keratoplasty (PKP, 8.0/8.1 mm) was performed in the left eye. The corneal explant was investigated by light and transmission electron microscopy. RESULTS: Best-corrected visual acuity was 20/40 six weeks after PKP. Light microscopy demonstrated a stromal ulceration down to the APCS lenticule. No stromal cells could be found within the APCS lenticule eight months after implantation. The APCS lenticule did not show a green stain of the collagens with Masson-Goldner staining and exhibited a strong Periodic acid-Schiff positive reaction. Electron microscopy of the APCS lenticule revealed cross-linked collagen lamellae without cellular components. Close to the interface, corneal collagen lamellae of the host cornea were disorganized. Few vital keratocytes were present on the surface of the lenticule and appeared to cause mechanical disruption of the host stroma along the lenticule-stroma interface. CONCLUSION: APCS implantation may lead to severe complications such as ulcerative keratopathy in otherwise uncomplicated KC corneas. In such cases, excimer laser-assisted PKP or Deep Anterior Lamellar Keratoplasty are the methods of choice to restore visual acuity.