Corneal Rigidity Research Articles

ANALYSIS OF THE EFFECTIVENESS OF SCLEROPLASTIC OPERATIONS IN CHILDREN WITH PROGRESSIVE MYOPIA WITH LONG-TERM FOLLOW-UP. NEW POSSIBILITIES OF DRUG TREATMENT OF PROGRESSIVE MYOPIA

There were performed a retrospective study of scleroplasty results in patients with progressive myopia (1282 eyes) and a prospective study of patients with myopia after scleroplasty (192 eyes). The age of patients is from 5 to 17 years, mean age is (12,5 ± 0,07) years. The observation period is from 1 to 7 years. The studies showed slowing rate of myopia progression after sclera operations in the majority of operated patients - in 92 % of cases. The maximum stabilizing effect of scleroplasty is observed one year after the operation. After 4 years and 7 years after operation the stabilizing effect is reduced. The combination of weakness of accommodation, constantly redundant tension of accommodation (CRTA) and finding intraocular pressure values in the upper normal range indicate the progression of myopia. The use of 0,005 % solution of Latanoprost (Prolatan) in the complex treatment of patients with myopia leads to normalization of intraocular pressure, increase of corneal hysteresis and rigidity index of corneoscleral membrane, as well as increase in the coefficient of accommodative response and decrease in the coefficient of the ciliary body microfluctuations.

BIOMECHANICAL PROPERTIES OF THE CORNEOSCLERAL MEMBRANE OF THE EYE WITH PROGRESSIVE MYOPIA BEFORE AND AFTER SCREROPLASTICS

There were examined 136 patients with progressive myopia (192 eyes) in the main group and 113 patients (113 eyes) with stationary myopia. The age of patients is from 8 to 17 years, mean age is (12,5 ± 0,07) years. The observation period is from 1 to 7 years. We also examined 46 patients with emmetropia (46 eyes) and 30 patients with low-grade hyperopia (30 eyes) from 6 to 17 years. It was established that the progression of myopia is characterized by an increase in the anteroposterior size of the eye, a decrease in the thickness of the sclera, a decrease in the corneal hysteresis and rigidity of the corneoscleral membrane is accompanied in 83,3 % of cases by an increase in intraocular pressure to the upper norm and above, which eventually leads to an increase in the strain of the corneoscleral membrane, a decrease in the biomechanical properties of the sclera and the progression of myopia.

Reevaluating the Effectiveness of Corneal Collagen Cross-linking and Its True Biomechanical Effect in Human Eyes

ABSTRACT The induction of cross-links in corneal tissue appears to be a promising technique to increase its stiffness and this has been the basis of treatment of keratoconus (KC) and corneal ectatic disease. However, there exists a striking discrepancy between the reported biomechanical effects of corneal collagen cross-linking (CXL) in vitro compared to in vivo, and this has not received much attention in the literature. Despite the documentation of an increase in corneal stiffness in vitro by many investigators, reports that provide evidence of measurable and consistent biomechanical changes in corneal rigidity in vivo after CXL are lacking. Indeed, the absence of documented in vivo biomechanical improvement in CXL-treated corneas is a conundrum, which needs to be further explored. To explain this discrepancy, it has been postulated that biomechanical changes induced by CXL are too subtle to be measured by currently available diagnostic tools or have characteristics not discernible by these technologies. However, the dynamic bidirectional applanation device (Ocular Response Analyzer) and dynamic Scheimpflug analyzer instruments (Corvis ST) have demonstrated the ability to quantify even subtle biomechanical differences in untreated KC corneas of different ectatic degree, and document the reduction in corneal hysteresis (CH) and corneal resistance factor (CRF) in situations where the corneal stiffness is reduced, such as after laser in situ keratomileusis and surface ablation procedures. It has also been possible to demonstrate an altered CH and CRF in patients with diabetes, smoking habit, glaucoma, Fuchs’ dystrophy, and corneal edema. It is puzzling that these diagnostic tools could document subtle biomechanical changes in these situations, yet fail to measure the purported changes induced by CXL on corneas with progressive KC. This failure to document significant and consistent biomechanical changes in corneal rigidity could suggest that CXL does not induce a simple reversal of the particular biomechanical deficits that characterize KC, or make the cornea significantly more resistant to bending forces as has been widely postulated. The absence of measurable biomechanical change in living KC corneas after CXL could be a consequence of biomechanical strengthening which is insignificant compared to the marked weakening caused by preexisting alteration of the collagen structure, disorganization of collagen fiber intertwining, and compromised structural–mechanical homogeneity that are hallmarks of keratoconic disease, especially in corneas with progressive KC. The changes in the cornea induced by CXL that have been described in vivo may instead be driven by a wound healing process in response to the removal of the corneal epithelial layer and subsequent exposure to riboflavin and ultraviolet-A (UVA). This paper will present evidence that sustains this hypothesis. How to cite this article Gatinel D. Reevaluating the Effect­iveness of Corneal Collagen Cross-linking and Its True Biomechanical Effect in Human Eyes. Int J Kerat Ect Cor Dis 2017;6(1):34-41.

Goldmann tonometer error correcting prism: clinical evaluation.

PurposeClinically evaluate a modified applanating surface Goldmann tonometer prism designed to substantially negate errors due to patient variability in biomechanics.MethodsA modified Goldmann prism with a correcting applanation tonometry surface (CATS) was mathematically optimized to minimize the intraocular pressure (IOP) measurement error due to patient variability in corneal thickness, stiffness, curvature, and tear film adhesion force. A comparative clinical study of 109 eyes measured IOP with CATS and Goldmann prisms. The IOP measurement differences between the CATS and Goldmann prisms were correlated to corneal thickness, hysteresis, and curvature.ResultsThe CATS tonometer prism in correcting for Goldmann central corneal thickness (CCT) error demonstrated a reduction to <±2 mmHg in 97% of a standard CCT population. This compares to only 54% with CCT error <±2 mmHg using the Goldmann prism. Equal reductions of ~50% in errors due to corneal rigidity and curvature were also demonstrated.ConclusionThe results validate the CATS prism’s improved accuracy and expected reduced sensitivity to Goldmann errors without IOP bias as predicted by mathematical modeling. The CATS replacement for the Goldmann prism does not change Goldmann measurement technique or interpretation.

Peculiarities of Biomechanical Properties of Ocular Tissue in Keratoconus

Considerable achievements having been recently made in modern diagnostics and treatment of keratoconus have not diminished the urgency of the given problem as the traditional views of the pathogenesis of keratoconus do not always allow to struggle effectively with this difficult and continuously progressing disease.The objective of the research was to study the peculiarities of biomechanical properties of the cornea in keratoconus.Materials and methods. The article presents the analysis of studying biomechanical properties of the cornea in keratoconus. 44 patients (88 eyes) with keratoconus and emmetropic refraction were examined. To calculate biomechanical indicators of the cornea there was carried out the comparative analysis between the measurements obtained with the use of several methods in the same patients, namely the Oculus Pentacam-Scheimpflug imaging device by a standard technique and the indicators calculated using the method proposed by us and the device for in vivo estimation of corneal rigidity.Results. Considerable advantages of using the developed method and the device for estimation of corneal rigidity in vivo in comparison with keratotopography on the Oculus Pentacam-Scheimpflug camera were registered which allowed us not only to reveal the presence of biomechanical disorders of the cornea, but also to differentiate their character. To describe the degree of changes in biomechanical properties of the cornea in vivo the coefficient of corneal rigidity was developed.Conclusions. Loading tests allow receiving more exact information on biomechanical properties of the cornea in comparison with standard researches on the Oculus Pentacam-Scheimpflug camera.

Displacement of the Lamina Cribrosa in Response to Acute Intraocular Pressure Elevation in Normal Individuals of African and European Descent.

PurposeTo assess if the in vivo mechanical displacement of the anterior laminar cribrosa surface (ALCS) as a response of an acute elevation in intraocular pressure (IOP) differs in individuals of European (ED) and African descent (AD).MethodsSpectral-domain optical coherence tomography (SDOCT) scans were obtained from 24 eyes of 12 individuals of AD and 18 eyes of 9 individuals of ED at their normal baseline IOP and after 60 seconds IOP elevation using ophthalmodynamometry. Change in depth (displacement) of the LC and to the prelaminar tissue (PLT) were computed in association with the change (delta) in IOP (Δ IOP), race, age, corneal thickness, corneal rigidity (ocular response analyzer [ORA]), and axial.ResultsIn the ED group for small IOP elevations (Δ IOP < 12 mm Hg), the ALCS initially displaced posteriorly but for larger increase of IOP an anterior displacement of the lamina followed. Inversely, in the AD group the ALCS did not show a significant posterior displacement for small Δ IOP, while for larger IOP increases the ALCS significantly displaced posteriorly. Posterior displacement of the lamina cribrosa (LC) was also significantly correlated with longer axial length, higher corneal thickness, and ORA parameters. Prelaminar tissue posteriorly displaced for any magnitude of Δ IOP, in both groups.ConclusionsThe African descent group demonstrated a greater acute posterior bowing of the LC after adjustment for age, axial length, Bruch's membrane opening (BMO) area, and ORA parameters. Greater PLT posterior displacement was also seen in the AD group with increasing IOP, which was tightly correlated with the displacement of the LC.

Intraocular Pressure and Trabecular Meshwork Outflow Facility After Descemet Stripping Endothelial Keratoplasty.

Increased intraocular pressure (IOP) is a frequent complication after penetrating keratoplasty and can be due to reduced trabecular meshwork outflow facility. Descemet stripping endothelial keratoplasty (DSEK) is a lamellar technique for replacing pathologic corneal endothelium and may be associated with a lower risk of postoperative IOP rise. In a prospective clinical study we studied IOP and outflow facility before and after DSEK. In 23 eyes of 23 patients before, 1 day, 6 weeks, and 3, 6, and 12 months after DSEK, IOP was measured using Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT). Trabecular meshwork outflow facility (C-value) was assessed by impression tonography with the Schioetz tonometer. Central corneal thickness was measured by Haag-Streit pachymetry. Best spectacle corrected visual acuity, ocular surface fluorescein staining, and corneal sensation were also recorded. Mean IOP showed a trend toward increase from preoperatively to 1 year postoperatively, which was not statistically significant (GAT: 13.5±3.3 to 15.3±4.7 mm Hg; DCT: 13.7±2.9 to 16.7±4.8 mm Hg; Schioetz: 12.4±2.8 to 15.3±2.9 mm Hg). Outflow facility increased significantly from 0.19±0.03 before to 0.29±0.05 mm/Δmm Hg/min at 1 year after DSEK (P=0.002). Best spectacle corrected visual acuity increased significantly from 0.98±0.48 to 0.36±0.17 logMAR (P=0.0004). Corneal sensitivity was unchanged and corneal staining significantly decreased from the preoperative to 1 year postoperative period (P=0.01). Mean central corneal thickness changed significantly from 650±59 to 621±73 μm (P=0.002). IOP as measured by GAT, DCT, and Schioetz tends to increase during the first year after DSEK in eyes without previous glaucoma, whereas trabecular meshwork outflow facility as measured by Schioetz tonography improves. These findings are likely to be due to a progressive increase of corneal rigidity affecting transcorneal pressure measurements of both IOP and trabecular meshwork outflow facility.

Ex vivo human cornea rigidity after UVA/riboflavin induced cross-linking

ObjectiveThe purpose of the current study was to assess changes in human corneal rigidity after treatment with riboflavin and UVA using a new device, the Corneal Displacement Unit (CDU). DesignExperimental study. The CDU was designed to quantitatively measure the effect of cross-linking (CXL) in complete human donor cornea buttons. This apparatus measures the tissue displacement associated to computer-controlled variations in pressure. MethodsBaseline measurements with the CDU were taken from 10 de-epithelialized human corneas. They were exposed to 0.1% riboflavin drops every 2min for 1h with exposure to UVA light during the last 30min after which CDU measurements were taken again. Results were analyzed using a non-parametric test. Significant tests were set at P≤.15 and non-significant correlation coefficients at rho≤.15 to reject abnormal measurements. For each of the 10 corneas, pachymetry values and 1988 CDU measurements were collected before and after treatment. ResultsPressure measurements averaged across the corneas were similar before and after treatment (P≥.99), and were highly correlated (Spearman rho=.88, P<.001). Corneal displacement observations after treatment were significantly different from baseline, showing a reduction of .084 microns on average (P<.001), and thus demonstrating a reduced displacement in cross-linked corneas. ConclusionsThe present study demonstrated a significant increase in the mechanical rigidity of human corneas after CXL. The CDU was able to quantify the mechanical strength of whole corneal buttons ex vivo with minimal damage to the tissue.

Corneal collagen cross-linking combined with simulation of femtosecond laser-assisted refractive lens extraction: an ex vivo biomechanical effect evaluation.

To evaluate biomechanical changes induced by in situ corneal cross-linking (CXL) with stromal pocket delivered enhanced concentration riboflavin and high-fluence, high-energy UV-A irradiation. Eight human donor corneas were subjected to intrastromal lamellar corneal tissue removal of anterior 140-μm deep, 80-μm thick × 5-mm diameter central stromal buttons, extracted through a 3.5-mm width tunnel, surfacing in the superior cornea periphery. Enhanced concentration riboflavin solution (0.25%) was instilled in the pocket. In study group A (CXL), superficial high-fluence UV-A irradiation was applied, whereas in control group B (no CXL), none. To comparatively assess changes in corneal rigidity, corneal specimens were subjected to transverse biaxial resistance measurements by application of a unidirectional tangential shear force. Biomechanical differences were evaluated through stress and Young shear modulus. Stress at 10% strain was 305 ± 24 kPa in study group A versus 157 ± 11 kPa in control group B (relative difference Δ = 107%, P = 0.021). Stress at 20% strain was 1284 ± 34 kPa in study group A versus 874 ± 29 kPa in control group B (Δ = 47%, P = 0.043). Average shear modulus in study group A at 10% strain was 6.98 ± 1.12 MPa versus 4.04 ± 0.85 MPa in control group B (Δ = 73%, P = 0.036). Average shear modulus in study group A at 20% strain was 11.46 ± 0.75 MPa versus 8.80 ± 0.72 MPa in group B (Δ = 30%, P = 0.047). Adjunct CXL in this ex vivo simulation refractive lens extraction procedure seems to provide significant increase in corneal rigidity, up to +107%. These findings also support our previous reported work on laser in situ keratomileusis combined with CXL.

High-irradiance CXL combined with myopic LASIK: flap and residual stroma biomechanical properties studied ex-vivo

Background/aimsTo evaluate ex vivo biomechanical and enzymatic digestion resistance differences between standard myopic laser in-situ keratomileusis (LASIK) compared with LASIK+CXL, in which high-irradiance cross-linking (CXL) is added.MethodsEight human donor corneas...

Short-term comparison of accelerated and standard methods of corneal collagen crosslinking

To compare the 6-month results of accelerated and standard collagen crosslinking (CXL) treatment of progressive keratoconus. Noor Eye Hospital, Tehran, Iran. Prospective randomized clinical trial. Two groups of eyes (intervention and control) received corneal collagen crosslinking (CXL) treatment. The intervention group received accelerated CXL (18 mW/cm(2), 5 minutes), and the control group received standard CXL (3 mW/cm(2), 30 minutes). The eyes were evaluated for changes in the visual indices, refraction, and topography preoperatively and 1, 3, and 6 months postoperatively and regarding corneal rigidity indices and the endothelial cell count (ECC) preoperatively and at 6 months. The study evaluated 62 eyes (31 patient) in 2 groups. The mean changes in uncorrected (P = .733) and corrected (P = .646) distance visual acuities and manifest refraction spherical equivalent (P = .598) did not differ statistically significantly between the 2 groups. The central corneal thickness was higher in the standard group than the accelerated group (P = .025). The mean decrease in the maximum keratometry (K) (P = .865) and mean K (P = .974) and the mean changes in the asphericity (P = .272) were not statistically significantly different between the 2 groups. The mean changes in corneal hysteresis (CH) (P = .548) and the corneal resistance factor (CRF) (P = 1.000), CH-CRF (P = .282), and the area under the peak 2 (P = .260) were similar in both groups. The mean decrease in the ECC was not statistically significantly different between the 2 groups (P = .218). Based on 6-month results, accelerated and standard corneal CXL arrested the progression of keratoconus similarly. No author has a financial or proprietary interest in any material or method mentioned.

Evaluation of corneal biomechanics before and after up-to-date keratoplasty in patients with bullous keratopathy

Aim - to study biomechanical properties of the cornea in patients with bullous keratopathy before and after keratoplasty. Ocular response analyzer (ORA, Reichert) indices were studied in 37 patients (37 eyes) with bullous keratopathy before and after surgery - in 1, 2, and 6 months and then in 1, 2, 3, and 5 years. The following keratoplasty modifications were performed: ultrathin Descemet's stripping automated endothelial keratoplasty (UTDSAEK) - in 17 cases, microkeratome-assisted posterior keratoplasty (MAPK) - in 13 cases, half top-hat penetrating keratoplasty (HTH PK) - in 7 cases. Corneal hysteresis (CH) and corneal resistance factor (CRF) values were significantly decreased in non-operated bullous keratopathy eyes as compared to healthy ones (p<0.05). By the 6-month follow-up these parameters have been found to be partially recovered and stabilized in all groups, however, still lower than normal (p<0.05). Differences between the groups were never statistically reliable, not at any time after surgery. Moreover, in eyes with bullous keratopathy, the mean corneal-compensated intraocular pressure (IOPcc) exceeded the mean Goldman-related IOP (IOPg) by 2.4 mmHg. One month after keratoplasty the difference between IOPcc and IOPg was 2.7, 4.3, and 3.6 mmHg in the MAPK, UTDSAEK, and HTH PK group, respectively; in 6 months - 2.6; 2.4 and 3.6 mmHg, respectively (p<0.05). In the fellow healthy eyes the two IOP measurements were not statistically different. Chronic edema of the cornea results in alteration of its viscoelastic properties. It has been shown that CH and CRF values decrease significantly in the eye involved as compared to the fellow healthy eye. After keratoplasty, regardless of the exact modification, these parameters partially recover, but remain lower than normal for at least 5 years as it was in our study. Neither before the surgery (when the cornea is chronically swollen), nor after, does corneal thickness correlate with its biomechanical indices. Postoperative reduction in corneal rigidity in eyes with bullous keratopathy may be confusing and lead to underestimation of the true level of IOP, thus, causing delays in diagnosis of concomitant glaucoma.

Progressive hyperopic shift after radial keratotomy: possible causes

To describe possible causes of progressive hyperopia in patients who underwent radial keratotomy. The study enrolled 33 subjects who underwent radial keratotomy earlier in their lives, of them 15 controls (29 eyes, group 1) with no refractive error and 18 patients (35 eyes, group II) with progressive hyperopia. The number and type of keratotomy scars was determined during biomicroscopy. Biomechanical properties of the cornea were assessed by means of bidirectional applanation (Ocular Response Analyzer). Dynamic contour tonometry (Pascal) was also used for intraocular pressure (IOP) measurement. Evaluation of the optic nerve head and retina included standard automated perimetry (Humphrey Field Analyzer) and confocal scanning laser ophthalmoscopy with Heidelberg Retinal Tomograph (HRT III). Group II showed reliable signs of low corneal rigidity, namely reduction of CH and CRF values (by 2.4 and 1.6 mmHg respectively) and central corneal thickness (by 56 microns) as compared to the controls. Tonometry results differed inconsiderably showing a tendency toward hypertension in both groups. The interquartile range of IOP was 17.8 ÷ 22.4 mmHg in group II and 16.3 ÷ 20.6 mmHg in group I. Changes in retinal light sensitivity and optic nerve head parameters were more pronounced in the controls. Several reasons for lowering of corneal rigidity can be suggested: initial biomechanical parameters of the cornea, surgical interference, and age-related changes. We think that hyperopic shift results from the combination of low corneal rigidity and increased IOP, i.e. not the lamina cribrosa but the cornea becomes the target of ocular hypertension. Thus, patients with weakened corneal refraction after radial keratotomy are at risk for developing glaucoma in the late postoperative period.

Collagen Cross-linking for the Treatment of Keratoconus in Pediatric Patients

ABSTRACT Keratoconus (KC) is a bilateral noninflammatory, ectatic corneal disorder. It is the most common primary ectasia affecting approximately 1 in 2,000 in the general population. Classically, the disease starts in puberty and progresses throughout the 3rd or 4th decades of life. Ocular signs and symptoms vary depending on disease severity. As the disease progresses, approximately 20% of KC eyes require penetrating keratoplasty. Collagen cross-linking (CXL) with ultraviolet-A (UVA) light and riboflavin is a new treatment that has emerged in the recent years. It is reported to slow the progression of the disease in its early stages, by increasing corneal rigidity and biomechanical stability. As the number of adult KC patients treated using this procedure grew, proving its safety and high efficacy, the pediatric KC patients population has started to receive special attention. In the pediatric KC patients’ eyes, corneas have been shown to be significantly steeper at the time of diagnosis compared to adults, and the severity of KC seems inversely correlated with age. Since treating KC in earlier age may be beneficiary, before developing an advanced disease that may require corneal transplantation, CXL in the pediatric age group has been advocated by many practitioners. The aim of this review is to collect and consolidate all known data regarding the efficacy and safety of CXL in the pediatric population. How to cite this article Hanna R, Berkwitz E, Castillo JH, Tiosano B. Collagen Cross-linking for the Treatment of Keratoconus in Pediatric Patients. Int J Kerat Ect Cor Dis 2015;4(3):94-99.

Long-term safety and efficacy of high-fluence collagen crosslinking of the vehicle cornea in Boston keratoprosthesis type 1.

The aim of this study was to evaluate the safety and efficacy of very high-fluence collagen crosslinking (CXL) as a means of achieving increased corneal rigidity and reduced enzymatic digestion in the vehicle cornea of Boston keratoprosthesis (KPro) type 1. Eleven consecutive patients fitted with a KPro (5 with a previous repeat cornea graft failure, 4 with ocular cicatricial pemphigoid, and 2 with chemical burn) underwent donor vehicle cornea pretreatment with very high-fluence prophylactic CXL in a 2-step procedure. First, the donor cornea was crosslinked with an intrastromal riboflavin instillation through a femtosecond laser-created pocket. This was followed up with a superficial CXL treatment. On the completion of the CXL pretreatment, the cornea center was trephined with the femtosecond laser, and the KPro was fitted onto the crosslinked donor cornea. Visual acuity, corneal surface, and donor vehicle cornea stability were evaluated. Follow-up evaluations were conducted over the next 9 years with a mean of 7.5 years. Mean uncorrected visual acuity improved from light perception to 20/60. One patient required a follow-up surgery, because of significant melt in the host cornea. None of the eyes developed melts and/or infection, especially on the vehicle cornea on which the KPro was fitted. Pretreatment with intrastromal and superficial very high-fluence CXL in conjunction with Boston type 1 KPro seems to be a safe and effective adjunctive treatment for achieving increased vehicle donor cornea rigidity. Additionally, there is an increased resistance to enzymatic degradation. This application may serve to enhance the biomechanical stability and external disease resistance of the donor vehicle cornea in patients with advanced external disease.

Effect of Ocular Biomechanics on Intraocular Pressure Measurement in Mucopolysaccharidosis I-S (Scheie’s Syndrome)

Purpose: To study the effect of biomechanical properties of the cornea on the intraocular pressure in eyes affected with Mucopolysaccharidosis type I-S (Scheie's syndrome). Methods: Four eyes of two patients in their mid-fifties diagnosed with Scheie's syndrome were investigated for corneal biomechanical properties. The corneal biomechanical profile was assessed by the use of Ocular response analyzer (ORA, Reichert Inc., of Buffalo, NY). Intraocular pressures were also checked using various tonometry devices to check for variability in the readings due to the corneal changes. Results: The intraocular pressure (IOP) measurements were noted to be high in both the patients at their initial presentation. Both the patients were put on topical anti glaucoma treatment and one underwent glaucoma filteration surgery as well for IOP control. Both the patients underwent successful bilateral deep anterior lamellar keratoplasty (DALK) procedures. The post procedure IOP measurement had a dramatic improvement in both the patients. Corneal biomechanical profile was noted to be high pre DALK and reduced significantly after the lamellar surgery. The intraocular pressure readings were also measured using different tonometry devices and were noted to be lower after graft surgeries. Conclusion: Corneal rigidity and hysteresis is high in patients with MPS type I-S. This is reflected in the raised intraocular pressures checked by use of applanation or indentation tonometry. Use of the ocular response analyzer has helped study the biomechanical properties of such corneas and helped in assessment of true values of intraocular pressures thus preventing inappropriate intervention options especially surgical options.

Imaging mass spectrometry by matrix-assisted laser desorption/ionization and stress-strain measurements in iontophoresis transepithelial corneal collagen cross-linking.

Purpose. To compare biomechanical effect, riboflavin penetration and distribution in transepithelial corneal collagen cross-linking with iontophoresis (I-CXL), with standard cross linking (S-CXL) and current transepithelial protocol (TE-CXL). Materials and Methods. The study was divided into two different sections, considering, respectively, rabbit and human cadaver corneas. In both sections corneas were divided according to imbibition protocols and irradiation power. Imaging mass spectrometry by matrix-assisted laser desorption/ionization (MALDI-IMS) and stress-strain measurements were used. Forty-eight rabbit and twelve human cadaver corneas were evaluated. Results. MALDI-IMS showed a deep riboflavin penetration throughout the corneal layers with I-CXL, with a roughly lower concentration in the deepest layers when compared to S-CXL, whereas with TE-CXL penetration was considerably less. In rabbits, there was a significant increase (by 71.9% and P = 0.05) in corneal rigidity after I-CXL, when compared to controls. In humans, corneal rigidity increase was not significantly different among the subgroups. Conclusions. In rabbits, I-CXL induced a significant increase in corneal stiffness as well as better riboflavin penetration when compared to controls and TE-CXL but not to S-CXL. Stress-strain in human corneas did not show significant differences among techniques, possibly because of the small sample size of groups. In conclusion, I-CXL could be a valid alternative to S-CXL for riboflavin delivery in CXL, preserving the epithelium.

Evaluation of iridociliary and lenticular elasticity using shear-wave elastography in rabbit eyes.

A previous study has employed shear-wave ultrasound elastographic imaging to assess corneal rigidity in an ex-vivo porcine eye model. This study employs the same modality in vivo in a rabbit eye model in order to assess lens, ciliary body and total ocular rigidity changes following the instillation of atropine and pilocarpine. Ten non-pigmented female rabbits were examined. Measurements of the lens, ciliary body and total ocular rigidity as well as lens thickness and anterior chamber depth were taken with the Aixplorer system (SuperSonic Imagine, Aix-en-Provence, France) with the SuperLinear™ SL 15-4 transducer in both eyes at baseline as well as after pilocarpine and atropine instillation. The IOP was also measured with the TonoPen tonometer. Changes in rigidity in the examined areas following atropine instillation were statistically not significant. Ciliary body rigidity was significantly increased whereas lens and total ocular rigidity were significantly reduced following pilocarpine instillation. The decrease in lens rigidity following pilocarpine was significantly associated with the respective increase in ciliary body rigidity. Shear-wave ultrasound elastography can detect in vivo rigidity changes in the anterior segment of the rabbit eye model and may potentially be applied in human eyes, providing useful clinical information on conditions in which rigidity changes play an important role, such as glaucoma, pseudoexfoliation syndrome or presbyopia.

Device for Calibration of the TVGD-01 Dynamic Tonometer

A device for calibration of a dynamic tonometer was developed. The principle of operation of the device is based on measurement of the rigidity of a dynamic system comprising a vibrator and the elastic surface of the eye. The rigidity is determined by monitoring the oscillation period of the system. The rigidity of the cornea is mathematically correlated with eye pressure. A flat spring with given parameters is suggested as a model of corneal rigidity at a given intraocular pressure. The error of determination of the flat spring rigidity was found to be due to imperfect manufacture and the error in measurement of the period of its free oscillation.

Contributing Factors to Corneal Deformation in Air Puff Measurements

Air puff systems have been presented recently to measure corneal biomechanical properties in vivo. In our study we tested the influence of several factors on corneal deformation to an air puff: IOP, corneal rigidity, dehydration, presence of sclera, and in vivo versus in vitro conditions. We used 14 freshly enucleated porcine eyes and five human donor eyes for in vitro experiments; nine human eyes were used for in vivo experiments. Corneal deformation was studied as a function of: IOP ranging from 15 to 45 mm Hg (in vitro); dehydration after riboflavin-dextran instillation (in vitro); corneal rigidity after standard ultraviolet (UV) corneal crosslinking (CXL, in vitro); boundary conditions, that is effect of the presence of the sclera (comparing corneal buttons and whole globes in vitro in pigs); and effect of ocular muscles (comparing human whole globes in vitro and in vivo). The temporal corneal deformation was characterized by the apex indentation across time, the maximal indentation depth, and the temporal symmetry (comparing inward versus outward deformation). The spatial corneal profile was characterized by the peak distance at maximal deformation. Temporal and spatial deformation profiles were very sensitive to the IOP (P < 0.001). The sclera slightly affected the temporal symmetry, while the ocular muscles drastically changed the amount of corneal recovery. CXL produced a significant (P = 0.001) reduction of the cornea indentation (by a factor of 1.41), and a change in the temporal symmetry of the corneal deformation profile (by a factor of 1.65), indicating a change in the viscoelastic properties with treatment. Corneal deformation following an air puff allows the measurement of dynamic properties, which are essential for the characterization of corneal biomechanics.