Ratiometric Sensing of Azithromycin and Sulfide Using Dual Emissive Carbon Dots: A Turn On-Off-On Approach.

A novel ratiometric fluorescence probe was developed for the determination of azithromycin (AZM) and sulfide ions based on the differential modulation of red emissive carbon dots (R-N@CDs) and blue emissive carbon dots (B-NS@CDs). The addition of sulfide anion selectively quenched the red emission of R-N@CDs while the blue emission of B-NS@CDs unaffected. Upon subsequent introduction of AZM to this R-N@CDs@sulfide system, the quenched red fluorescence was restored. Comprehensive characterization of the CDs was performed using UV-Vis, fluorescence, FTIR spectroscopy, XPS, and TEM. The proposed method exhibited excellent sensitivity and selectivity, with limits of detection of 0.33 µM for AZM and 0.21 µM for sulfide. Notably, this approach enabled direct detection of sulfide without requiring prior modulation of the CDs with metal ions, as is common in other reported methods. The ratiometric probe was successfully applied for the determination of AZM in biological fluids and sulfide in environmental water samples with high selectivity. This work presents the first fluorometric method for the detection of AZM in biological fluids.

Methylene blue-assisted molecularly-imprinted film modified nitrogen and sulfur co-doped molybdenum carbide for simultaneous electrochemical determination of two hepatotoxic drugs.

A novel electrochemical sensor with a dual-template molecular imprinting technology was fabricated for the simultaneous detection of paracetamol (PAR) and isoniazid (INZ). The sensor was constructed using nitrogen and sulfur co-doped molybdenum carbide (N, S@Mo2C) and a thin layer of electro-polymerized methylene blue was applied onto the surface of the N, S@Mo2C. The electrochemical sensor demonstrated remarkable analytical efficiency for the concurrent PAR and INZ quantification under optimal circumstances. The system achieved an exceptionally low limit of detection (S/N = 3) of  3.7 nM for PAR, with a concentration range  of  0.013 and 140 µM.  A LOD of 7.6 nM was attained for INZ, with a linear range  between 0.025 and 140 µM. Furthermore, the platform's selectivity was evaluated using differential pulse voltammetry  (DPV). The designed platform successfully detected PAR and INZ in authentic samples with recoveries varying between 98.3% and 104.9%. The relative standard deviations (RSD) for these measurements ranged from 2.7 to 4.0%, demonstrating that the proposed sensor is extremely stable, repeatable, and reproducible. These promising results suggest that the sensor holds potential for the detection of various (bio) molecules, paving the way for future applications in sensing fields.

An innovative dual-signal electrochemical ratiometric determination of creatinine based on silver nanoparticles with intrinsic self-calibration property for bimetallic Prussian blue analogues.

An ultrasensitive dual-signal ratiometric electrochemical sensor was developed for creatinine detection utilizing silver nanoparticles (Ag) with intrinsic self-calibration afforded by iron-nickel bimetallic Prussian blue (FeNiPBA) analogues. The Ag@FeNiPBA exhibits two redox signals corresponding to the Ag+/Ag and Fe3+/Fe2+ systems. Adding chloride (Cl-) solution increases the anodic current of the Ag/Ag system significantly due to the formation of silver chloride through solid-state electrochemistry. While the anodic current of the Ag/Ag system decreases in the presence of creatinine due to the competitive reaction, the Fe/Fe system's anodic current remains the same, which enables a ratiometric response. Under optimized conditions, the response ratio (IAg/IFe) decreases while the creatinine concentration increases linearly between 0.015 and 140 µM, with 0.004 µM as a good detection limit (S/N = 3). These results demonstrate superior performance over previously reported methods for electrochemical creatinine determination. The high sensitivity arises from the signal amplification of the Ag/AgCl solid-state electrochemistry, while the selectivity originates from the specific interaction between Ag+ and creatinine. The Ag@FeNiPBA hybrid can quantify creatinine in real samples with good recoveries. This work opens up new opportunities for applying dual-signal nanostructures to develop electrochemical sensors for (bio)molecule detection.

Intereye Differences in the Clinical Assessment of Intraocular Pressure and Ocular Biomechanics.

SIGNIFICANCE: Clinicians and researchers will have evidence whether intereye differences confound clinical measurements of intraocular pressure or of ocular biomechanical parameters. PURPOSE: The purpose of this study was to determine whether intraocular pressure and biomechanical parameters, as measured by the Ocular Response Analyzer (ORA) and by Cornea Visualization with Scheimpflug Technology (CorVis ST), are different between the first and second eye measured. METHODS: Intraocular pressure and biomechanical parameters were collected from both eyes of healthy participants (N = 139). The ORA measured corneal-compensated intraocular pressure, Goldmann-correlated intraocular pressure, and corneal hysteresis. The CorVis ST measured biomechanically corrected intraocular pressure, stiffness parameter at first applanation, and stiffness parameter at highest concavity. For each measurement, a paired t test compared the value of the first eye measured against that of the second eye measured. RESULTS: For the ORA, Goldmann-correlated intraocular pressure was significantly higher ( P = .001) in the first eye (14.8 [3.45] mmHg) than in the second eye (14.3 [3.63] mmHg). For the CorVis ST, biomechanically corrected intraocular pressure was significantly higher ( P < .001) in the second eye (14.7 [2.14] mmHg) than in the first eye (14.3 [2.11] mmHg). Stiffness parameter at first applanation (intereye difference, 6.85 [9.54] mmHg/mm) was significantly ( P < .001) higher in the first eye than in the second eye. Stiffness parameter at highest concavity was significantly higher ( P = .01) in the second eye (14.3 [3.18] mmHg/mm) than in the first eye (14.0 [3.13] mmHg/mm). CONCLUSIONS: Although there were statistically significant intereye differences in intraocular pressure and in biomechanical parameters for both devices, the variations were small and thus unlikely to affect clinical outcomes.

Sonochemical synthesis of lanthanum ferrite nanoparticle-decorated carbon nanotubes for simultaneous electrochemical determination of acetaminophen and dopamine.

A new nanocomposite consisting of lanthanum ferrite nanoparticles (LaFeO3 NPs) integrated with carbon nanotubes (CNTs) was fabricated via facile sonochemical approach. The engineered nanocomposite was applied to simultaneously determine acetaminophen (ACP) and dopamine (DA) in a binary mixture. The LaFeO3 NPs@CNT probe possesses several advantages such as superior conductivity, large surface area, and more active sites, improving its electrocatalytic activity towards ACP and DA. Under optimized conditions, the anodic peak currents (Ipa) linearly increased with increasing concentration of ACP and DA in the range 0.069-210 µM and 0.15-210 µM, respectively. The sensitivity of LaFeO3 NPs@CNTs/glassy carbon electrode (GCE) for detecting ACP and DA is 7.456 and 5.980 µA·µM-1·cm-2, respectively. The detection limits (S/N = 3) for ACP and DA are 0.02 µM and 0.05 µM, respectively. Advantages of LaFeO3 NPs@CNTs/GCE for the detection of ACP and DA include wide linear ranges, low-detection limits, good selectivity, and long-term stability. The as-fabricated electrode was applied to determine ACP and DA in pharmaceutical formulations and human serum samples with recoveries ranging from 97.7 to 103.3% and an RSD that did not exceed 3.7%, confirming the suitability of the proposed sensor for the determination of ACP and DA in real samples. This study not only presents promising opportunities for enhancing the sensitivity and stability of electrochemical sensors used in the detection of bioanalytes but also significantly contributes to the progress of unique and comprehensive biochemical detection methodologies.

Ratiometric fluorometric determination of sulfide using graphene quantum dots and self-assembled thiolate-capped gold nanoclusters triggered by aluminum.

A ratiometric-based fluorescence emission system was proposed for the determination of sulfide. It consists of blue emissive graphene quantum dots (GQDs) and self-assembled thiolate-protected gold nanoclusters driven by aluminum ion (Al3+@GSH-AuNCs). The two types of fluorophores are combined to form a ratiometric emission probe. The orange emission of Al3+ @GSH-AuNCs at 624 nm was quenched in the presence of sulfide ion owing to the strong affinity between sulfide and Au(I), while the blue GQDs fluorescence at 470 nm remained unaffected. Interestingly, the Al3+@GSH-AuNCs and GQDs were excited under the same excitation wavelength (335 nm). The response ratios (F470/F624) are linearly proportional to the sulfide concentration within the linear range of 0.02-200 µM under the optimal settings, with a limit of detection (S/N = 3) of 0.0064 µM. The proposed emission probe was applied to detect sulfide ions in tap water and wastewater specimens, with recoveries ranging from 95.3% to 103.3% and RSD% ranging from 2.3% to 3.4%, supporting the proposed method's accuracy.

Highly selective and sensitive electrochemical determination of cysteine based on complexation with gold nanoparticle-modified copper-based metal organic frameworks.

A gold nanoparticle-modified copper-based metal organic framework (Au NPs@Cu-BDC) was fabricated for the electrochemical determination of cysteine (Cys-SH). The nanocomposites were characterized using different techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), powder X-ray spectroscopy (PXRD), thermogravimetry (TGA), nitrogen adsorption-desorption isotherms, and Fourier transform infrared spectroscopy (FTIR). Formation of a new anodic peak of Cu(II)-Cys complex at + 0.43 V was used to detect Cys-SH. Cyclic and square wave voltammetric studies proved that the Au NPs enhanced the conductivity of Cu-BDC. The proposed electrode exhibited a linear range of 0.0015-10.5 µM and low detection limit of 0.0004 µM with a good sensitivity of 0.78 ± 0.01 µA µM. The as-fabricated electrode was successfully used for the estimation of Cys-SH in real samples (human plasma, urine, and saliva) with recovery % of 99-100% and RSD % of 2.7-3.6%, respectively.

Double-signal quantification of amoxicillin based on interaction with 4-aminoantipyrine at copper and nitrogen co-doped carbon quantum dots as an artificial nanozyme.

An one-pot hydrothermal method was developed for synthesis of carbon quantum dots co-doped with copper and nitrogen (Cu, N@CQDs). The synthesized Cu, N@CQDs has unique advantages such as high fluorescence quantum yield (39.1%) and high catalytic activity. Oxidative coupling of amoxicillin (AMX) with 4-aminoantipyrine (4-NH2-APE) in the presence of H2O2 as an oxidant to produce pink quinoneimine chromogen was carried out with the aid of Cu, N@CQDs as a peroxidase-like catalyst. This system was used for the colorimetric and fluorometric assays of AMX with reliable results. Colorimetric method is based on the measurement of a pink-colored product at λmax = 505 nm while the fluorometric assay is based on the quenching of the fluorescence emission of Cu, N@CQDs at 440 nm after excitation at 370 nm. For the colorimetric method, the absorption intensity linearly increased over the concentration range 4.3-110.0 µM with LOD (S/N = 3) of 1.3 µM. For the fluorometric method, the emission intensity of Cu, N@CQDs linearly decreased upon addition of AMX in the concentration range 0.2-120.0 µM with a limit of detection (LOD, S/N = 3) of 0.06 µM. The proposed system was applied to the determination of AMX in different real samples such as pharmaceutical capsules, human serum, milk, and conduit water samples with recoveries in the range 95.8-104.1% and relative standard deviation (RSD %) less than 4.1%.

Effect of penetration enhancer with novel corneal cross-linking using recombinant human decoron in porcine eyes.

The aim of the study was to investigate the effectiveness of exogenous recombinant human decoron and an accompanying penetration-enhancing solution in stiffening ex-vivo porcine corneas both transepithelially and after de-epithelialization. Eight porcine paired eyes were treated transepithelially: one eye with a pre-treatment solution (Pre-Tx), penetration enhancing solution (PE), and decoron while the fellow eye was treated by the same protocol but without decoron. A second group included 4 de-epithelialized pairs treated identically. The final group included 4 de-epithelialized pairs with one eye treated with Pre-Tx, PE, and decoron while the fellow eye was treated without PE. Uniaxial tensile testing was used to compare the corneal stiffness between the different treatment conditions. Residual tissue underwent immunohistochemistry analysis to evaluate the depth of penetration of decoron into the corneal stroma. There was no stiffening effect exhibited among corneas treated transepithelially with decoron compared to control (P > 0.05) and poor stromal penetration was exhibited on tissue analysis. Among de-epithelialized corneas, there was a significant stiffening effect seen in those treated with decoron at 3%, 4%, 5%, & 6% strain (P < 0.05) compared to control. Among de-epithelialized corneas there was also a significant stiffening effect seen in those treated with the PE and decoron at 4%, 5%, & 6% strain (P < 0.05) with improved stromal penetration confirmed by immunohistochemistry, versus without PE. De-epithelialization is necessary for effective stromal penetration of decoron. Depth of penetration and subsequent corneal stiffening may be improved with a penetration enhancing solution. Compared to riboflavin, decoron requires shorter treatment time and spares UV light exposure.

Simultaneous electrochemical detection of azithromycin and hydroxychloroquine based on VS2 QDs embedded N, S @graphene aerogel/cCNTs 3D nanostructure.

In this research paper, an innovative electrochemical sensor was suggested for simultaneous voltammetric analysis of azithromycin (AZM) and hydroxychloroquine (HCQ) for the first time. The sensor based on hydrothermal synthesis of vanadium disulfide quantum dots (VS2 QDs) and insertion within 3D N, S graphene aerogel (3D N, S @ GNA) and carbon nanotubes nanaostructure as a new and widely group of carbon nanomaterials. The nanocomposites were characterized morphologically using different techniques. In addition, the nanomaterials were characterized electrochemically using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The proposed electrochemical sensor showed wide dynamic linear ranges of 0.28-30 × 10-8 M and 0.84-22.5 × 10-8 M for analysis of AZM and HCQ, respectively. The limits of detection (LODs) based on signal to noise (S/N) 3:1 were found to be 0.091 × 10-8 M and 0.277 × 10-8 M for AZM and HCQ, respectively. Briefly, the electrochemical sensor had good stability, selectivity, reproducibility and feasibility for simultaneous detection of AZM and HCQ in presence of different interfering species.

Facile one pot sonochemical synthesis of layered nanostructure of ZnS NPs/rGO nanosheets for simultaneous analysis of daclatasvir and hydroxychloroquine.

In this study, zinc sulfide nanoparticles were loaded on reduced graphene oxide (ZnS NPs/rGO) using simple sonochemical method. The nanocomposite was characterized using different morphological and electrochemical techniques such as TEM, SEM, PXRD, EDX, Raman spectroscopy, FTIR, N2-adsorption-desorption, CV, and EIS. The ZnS NPs/rGO modified glassy carbon electrode (GCE) was used to simultaneously estimate hydroxychloroquine (HCQ) and daclatasvir (DAC) in a binary mixture for the first time. The modified nanocomposite exhibited good catalytic activity towards HCQ and DAC detection. In addition, it showed higher sensitivity, good selectivity and stability; and high reproducibility towards HCQ and DAC analysis. The activity of the modified electrode was noticeably improved due to synergism between ZnS NPs and rGO. Under optimum conditions of DPV measurements, the anodic peak currents (Ipa) were obviously increased with the increase of HCQ and DAC amounts with linear ranges of 5.0-65.0 and 7.0-65.0 nM with LODs of 0.456 and 0.498 nM for HCQ and DAC, respectively. The ZnS NPs/ rGO modified GCE was used to quantify HCQ and DAC in biological fluids with recoveries of 98.7-102.7% and 96.9-104.5% and RSDs of 1.89-3.57% and 1.91-3.70%, respectively.

Ultrasensitive and selective molecularly imprinted electrochemical oxaliplatin sensor based on a novel nitrogen-doped carbon nanotubes/Ag@cu MOF as a signal enhancer and reporter nanohybrid.

A sensitive and selective molecular imprinted polymeric network (MIP) electrochemical sensor is proposed for the determination of anti-cancer drug oxaliplatin (OXAL). The polymeric network [poly(pyrrole)] was electrodeposited on a glassy carbon electrode (GCE) modified with silver nanoparticles (Ag) functionalized Cu-metal organic framework (Cu-BDC) and nitrogen-doped carbon nanotubes (N-CNTs). The MIP-Ag@Cu-BDC /N-CNTs/GCE showed an observable reduction peak at -0.14 V, which corresponds to the Cu-BDC reduction. This peak increased and decreased by eluting and rebinding of OXAL, respectively. The binding constant between OXAL and Cu-BDC was calculated to be 3.5 ± 0.1 × 107 mol-1 L. The electrochemical signal (∆i) increased with increasing OXAL concentration in the range 0.056-200 ng mL-1 with a limit of detection (LOD, S/N = 3) of 0.016 ng mL-1. The combination of N-CNTs and Ag@Cu-BDC improves both the conductivity and the anchoring sites for binding the polymer film on the surface of the electrode. The MIP-based electrochemical sensor offered outstanding sensitivity, selectivity, reproducibility, and stability. The MIP-Ag@Cu-BDC /N-CNTs/GCE was applied to determine OXAL in pharmaceutical injections, human plasma, and urine samples with good recoveries (97.5-105%) and acceptable relative standard deviations (RSDs = 1.8-3.2%). Factors affecting fabrication of MIP and OXAL determination were optimized using standard orthogonal design using L25 (56) matrix. This MIP based electrochemical sensor opens a new venue for the fabrication of other similar  sensors and biosensors.

Facile fabrication of a novel disposable pencil graphite electrode for simultaneous determination of promising immunosuppressant drugs mycophenolate mofetil and tacrolimus in human biological fluids.

An innovative electrochemical sensor was proposed for simultaneous determination of mycophenolate mofetil (Mph) and tacrolimus (TAC) for the first time. A novel sensor based on electro-polymerization of multi-walled carbon nanotubes (MWCNTs) and a novel Cu-1N-allyl-2-(2,5-dimethoxyphenyl)-4,5-diphenyl-1H-imidazole metal organic framework (Cu-ADPPI MOF) on disposable pencil graphite electrode (dPGE). Many techniques were used to characterize the electrochemical activity and surface structure of the fabricated sensor. The proposed sensor exhibited good catalytic performance towards Mph and TAC oxidation due to the synergistic effect. Under optimal conditions, the proposed sensor has achieved a linear range of 0.85-155 × 10-8 M and 1.1-170.0 × 10-8 M with LODs of 0.28 × 10-8 M and 0.36 × 10-8 M for Mph and TAC, respectively. The designated sensor showed good reproducibility, repeatability, stability, and selectivity for the determination of Mph and TAC. Moreover, the simultaneous determination of Mph and TAC in different human biological fluids was carried out with acceptable results. As a result, the proposed sensor opens a new venue for the use of electro-polymerized MOFs in combination with other conductive materials such as MWCNTs for electrochemical sensing of different analytes with the desired sensitivity and selectivity. Graphical abstract Construction of disposable graphite electrode, based on electro-deposition of multilayer films of multi-walled carbon nanotubes and a new generation of Cu-MOFs, for simultaneous analysis of tacrolimus and mycophenolate mofetil for the first time.

Modification of N,S co-doped graphene quantum dots with p-aminothiophenol-functionalized gold nanoparticles for molecular imprint-based voltammetric determination of the antiviral drug sofosbuvir.

A molecularly imprinted polymer (MIP) was developed for the electrochemical determination of the antiviral drug sofosbuvir (SOF). The MIP was obtained by polymerization of p-aminothiophenol (p-ATP) on N,S co-doped graphene quantum dots (N,S@GQDs) in the presence of gold nanoparticles to form gold-sulfur covalent network. The presence of quantum dots improves the electron transfer rate, enhances surface activity and amplifies the signal. The nanocomposites were characterized by FTIR, TEM, EDX, and SEM. The electrochemical performance of the electrode was investigated by differential pulse voltammetry and cyclic voltammetry. The sensor uses hexacyanoferrate as the redox probe and is best operated at a potential of around 0.36 V vs. Ag/AgCl. It has a linear response over the concentration range of 1-400 nM SOF, with a detection limit of 0.36 nM. Other features include high selectivity, good reproducibility and temporal stability. The sensor was applied to the determination of SOF in spiked human plasma. Graphical abstract Novel sofosbuvir imprinted p-ATP polymer was synthesized by the aid of gold nanoparticles on N,S co-doped graphene quantum dots as a good conductive support. The imprinted polymer was used for detection of sofosbuvir in real samples by using the ferri/ferrocyanide redox probe.

A Validated High-Throughput Fluorometric Method for Determination of Omeprazole in Quality Control Laboratory via Charge Transfer Sensitized Fluorescence.

A high-throughput 96-microwell plate fluorometric method was developed and validated to determine omeprazole (OMZ) in its dosage forms. The method was based on the charge-transfer (CT) sensitized fluorescence reaction of OMZ with 2, 3-dichloro-5, 6-dicyano-1, 4-benzoquinone (DDQ). This fluorescence reaction provided a new approach for simple, sensitive and selective determinations of OMZ in pharmaceutical preparations. In the present method, the fluorescence reaction was carried out in 96-microwell plates as reaction vessels in order to increase the automation of the methodology and the efficiency of its use in quality control laboratories. All factors affecting the fluorescence reaction were carefully studied and the conditions were optimized. The stoichiometry of the fluorescence reaction between OMZ and DDQ was determined and the reaction mechanism was suggested. Under the optimum conditions, the linear range was 100-6000 ng/ml with the lowest LOD of 33 ng/ml. Analytical performance of the proposed assay, in terms of accuracy and precision, was statistically validated and the results were satisfactory; RSD was <2.6 % and the accuracy was 98.6-101.6 %. The method was successfully applied to the analysis of OMZ in its dosage forms; the recovery values were 98.26-99.60 ± 0.95-2.22 %. The developed methodology may provide a safer, automated and economic tool for the analysis of OMZ in quality control laboratories.

Visual outcomes following optic nerve sheath fenestration via the medial transconjunctival approach.

This article determines the safety of optic nerve sheath fenestration (ONSF) for the treatment of patients with intracranial hypertension in the immediate 6-month post-operative period and its efficacy in reducing optic disk edema. Retrospective, non-comparative interventional case series. 207 eyes in 104 patients undergoing ONSF between the years 2005 and 2014. Papilledema grade based on modified Frisen scale and mean deviation of Humphrey visual field. 207 eyes of 104 patients (102 IIH, 2 IH due to dural sinus thrombosis) were included in the study. The patients were 96.1% female (N = 100) and 3.9% male (N = 4). The average patient age was 28.8 years (SD ± 9.5 years) and had a mean opening pressure of 39.85 cmH2O (SD ± 8.4 cmH2O). Mean follow-up period was 6.0 months (SD ± 5.9 months). Papilledema resolved in 76.1% of eyes at 1 week (N = 102 eyes), 75% of eyes at 1 month (N = 90 eyes), and 71% of eyes at 6 months (N = 94 eyes). Visual field comparison had a mean of the paired differences in MD at 1 week, 1 month, and 6 months of 1.59dB (P = 0.006), 2.53dB (P < 0.001), and 1.30dB (P = 0.016), respectively. ONSF is effective in reducing optic disk edema and does not cause vision loss in the 6-month post-operative period regardless of severity of IIH (as judged by elevation of opening pressure measured at pre-operative assessment).

Keratoconus cone location influences ocular biomechanical parameters measured by the Ocular Response Analyzer.

BACKGROUND: Keratoconus is characterized by asymmetry in the biomechanical properties of the cornea, with focal weakness in the area of cone formation. We tested the hypothesis that centrally-measured biomechanical parameters differ between corneas with peripheral cones and corneas with central cones. METHODS: Fifty participants with keratoconus were prospectively recruited. The mean ± standard deviation age was 38 ± 13 years. Axial and tangential corneal topography were analyzed in both eyes, if eligible. Cones in the central 3 mm of the cornea were considered central, and cones outside the central 3 mm were considered peripheral. Each eye was then measured with the Ocular Response Analyzer (ORA) tonometer. T-tests compared differences in ORA-generated waveform parameters between cohorts. RESULTS: Seventy-eight eyes were analyzed. According to the axial topography maps, 37 eyes had central cones and 41 eyes had peripheral cones. According to the tangential topography maps, 53 eyes had central cones, and 25 eyes had peripheral cones. For the axial-topography algorithm, wave score (WS) was significantly higher in peripheral cones than central cones (inter-cohort difference = 1.27 ± 1.87). Peripheral cones had a significantly higher area of first peak, p1area (1047 ± 1346), area of second peak, p2area (1130 ± 1478), height of first peak, h1 (102 ± 147), and height of second peak, h2 (102 ± 127), than central cones. Corneal hysteresis (CH), width of the first peak, w1, and width of the second peak, w2, did not significantly differ between cohorts. There were similar results for the tangential-topography algorithm, with a significant difference between the cohorts for p1area (855 ± 1389), p2area (860 ± 1531), h1 (81.7 ± 151), and h2 (92.1 ± 131). CONCLUSIONS: Cone location affects the biomechanical response parameters measured under central loading of the cornea. The ORA delivers its air puff to the central cornea, so the fact that h1 and h2 and that p1area and p2area were smaller in the central cone cohort than in the peripheral cone cohort suggests that corneas with central cones are softer or more compliant centrally than corneas with peripheral cones, which is consistent with the location of the pathology. This result is evidence that corneal weakening in keratoconus is focal in nature and is consistent with localized disruption of lamellar orientation.