Enucleated Porcine Eyes Research Articles

Imaging of intravitreal injected solution dispersion

PurposeThe extent of activity of an intravitreal injected drug is linked to its dispersion within the vitreous body. Researchers have been trying to visualize dispersion of intravitreal injected solutions using Indian ink or fluorescein, either with subsequent dissection or with endoillumination, both invasive methods that could influence the dispersion pattern. Therefore, this pilot study aims at investigating and identifying the best minimal invasive imaging method for visualizing the dispersion of an intravitreal injected solution.MethodsTo determine the optimal imaging concentration, a series of 5 enucleated porcine eyes were injected with 0.1 cc of 100%, 50%, 25%, 20% and 10% standard iodium contrast medium, respectively. Injections were made using a standard 1 cc syringe and 30 gauge needle at 3.5 mm from the limbus aiming at the center of the globe. Subsequently, the dispersion of the contrast agent was monitored using high resolution imaging methods: mammography and ultra high resolution computed tomography (UHRCT). For the latter, 3D reconstructions were rendered.ResultsA 1:10 dilution mixture combined optimal visualization contrast with low viscosity of the injection solution using radiographic ultrahigh resolution mammography. Both mammography and UHRCT images were taken from two eyes; one with a slow injection, the other with a fast injection.Conclusions3D reconstructed UHRCT images were favored over 2D mammography images for dynamic imaging of the intravitreal solution dispersion.

Cell penetrating peptide constructs: A novel drug delivery to the eye

PurposeIn neovascular age‐related macular degeneration (AMD) blood vessels grow from the choroid under the retina causing macular damage and scarring. Anti‐VEGF drugs such as, ranibizumab or aflibercept are administered by intravitreal injection to treat AMD related neovascularisation, We present a novel cell‐penetrating peptide construct (CPPC) topical delivery system to deliver Ranibizumab to the retina using drops.MethodsPeptides were produced using standard solid‐phase peptide synthesis. They were analysed using mass spectrometry and purified using high‐pressure liquid chromatography and used at a purity of >95%. CPPC were built around the drugs by vortexing for 10 seconds and incubating at room temperature. Drug delivery experiments were carried out ex‐vivo in freshly enucleated porcine eyes. In vivo experiments were carried out in C57 mice. Mice had a three 100 μm laser burns to the choroid to model neo‐vascularisation in AMD. They then received a single intravitreal injection of an anti‐VEGF agent or CPPC/Ranibizumab applied topically to the conjunctival sac twice daily for the duration of the experiment. Choroidal neovascularisation was measured by immunohistochemistry.ResultsEx vivo delivery to enucleated porcine eyes demonstrated that a single 60 μL drop could deliver 1.7 ± 0.4 μg/mL of ranibizumab to the vitreous cavity. Confocal images of immunohistochemistry on retinal wholemounts showed ranibizumab within the retina. In vivo experiments demonstrated both intravitreal injection and CPPC bound Ranibizumab reduced neovascularisation equally, compared to controlsConclusionsCPPC can be used topically to deliver therapeutic levels of Ranibizumab to the posterior segment.

Standard versus accelerated riboflavin–ultraviolet corneal collagen crosslinking: Resistance against enzymatic digestion

PurposeTo examine the effect of standard and accelerated corneal collagen crosslinking (CXL) on corneal enzymatic resistance.SettingSchool of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom.DesignExperimental study.MethodsSixty-six enucleated porcine eyes (with corneal epithelium removed) were assigned to 6 groups. Group 1 remained untreated, group 2 received dextran eyedrops, and groups 3 to 6 received riboflavin/dextran eyedrops. Group 4 had standard CXL (3 mW/cm2 ultraviolet-A for 30 minutes), whereas groups 5 and 6 received accelerated CXL (9 mW/cm2 for 10 minutes and 18 mW/cm2 for 5 minutes, respectively). Trephined central 8.0 mm buttons from each cornea underwent pepsin digestion. Corneal diameter was measured daily, and the dry weight of 5 samples from each group was recorded after 12 days of digestion.ResultsAll CXL groups (4 to 6) took longer to digest and had a greater dry weight at 12 days (P < .0001) than the nonirradiated groups (1 to 3) (P < .0001). The time taken for complete digestion to occur did not differ between the standard and accelerated CXL groups, but the dry weights at 12 days showed significant differences between treatments: standard CXL 3 mW > accelerated CXL 9 mW > accelerated CXL 18 mW (P < .0001).ConclusionsStandard and accelerated CXL both increased corneal enzymatic resistance; however, the amount of CXL might be less when accelerated CXL is used. The precise amount of CXL needed to prevent disease progression is not yet known.Financial DisclosureNo author has a financial or proprietary interest in any material or method mentioned.

Characterization of Corneal Indentation Hysteresis.

Corneal indentation is adapted for the design and development of a characterization method for corneal hysteresis behavior - Corneal Indentation Hysteresis (CIH). Fourteen porcine eyes were tested using the corneal indentation method. The CIH measured in enucleated porcine eyes showed indentation rate and intraocular pressure (IOP) dependences. The CIH increased with indentation rate at lower IOP (<; 25 mmHg) and decreased with indentation rate at higher IOP (> 25 mmHg). The CIH was linear proportional to the IOP within an individual eye. The CIH was positively correlated with the IOP, corneal in-plane tensile stress and corneal tangent modulus (E). A new method based on corneal indentation for the measurement of Corneal Indentation Hysteresis in vivo is developed. To our knowledge, this is the first study to introduce the corneal indentation hysteresis and correlate the corneal indentation hysteresis and corneal tangent modulus.

A frame-supported ultrathin electrospun polymer membrane for transplantation of retinal pigment epithelial cells

We report on the design and fabrication of a frame-supported nanofibrous membrane for the transplantation of retinal pigment epithelial (RPE) cells, which is a promising therapeutic option for the treatment of degenerative retinal disorders. The membranous cell carrier prepared from 640 nm-thick poly(DL-lactide) fibres uniquely combines high porosity, large pore size and low thickness, to maximize the nutrient supply to the transplanted cells in the subretinal space and thus to enhance the therapeutic effect of the transplantation. The carrier was prepared by electrospinning, which made it easy to embed a 95 μm-thick circular supporting frame 2 mm in diameter. Implantations into enucleated porcine eyes showed that the frame enabled the ultrathin membrane to be handled without irreversible folding, and allowed the membrane to regain its flat shape when inserted into the subretinal space. We further demonstrated that the minimum membrane thickness compatible with the surgical procedure and instrumentation employed here was as low as 4 μm. Primary porcine RPE cells cultivated on the membranes formed a confluent monolayer, expressed RPE-specific differentiation markers and showed transepithelial resistance close to that of the native RPE. Most importantly, the majority of the RPE cells transplanted into the subretinal space remained viable. The ultrathin, highly porous, and surgically convenient cell carrier presented here has the potential to improve the integration and the functionality of transplanted RPE cells.

Porcine Model to Evaluate Real-Time Intraocular Pressure During Femtosecond Laser Cataract Surgery

Purpose: To investigate the changes in intraocular pressure (IOP) in porcine eyes during femtosecond laser-assisted cataract surgery using a liquid-optic interface system.Materials and methods: Femtosecond laser cataract surgery with the Catalys™ was performed on freshly enucleated porcine eyes in Oftalvist Moncloa, Madrid, Spain. Capsulorhexis and lens fragmentation were completed in all the eyes without complications. IOP was measured with a reusable blood pressure transducer connected by direct cannulation to the anterior chamber, recording data before suction (basal), at the beginning of the suction phase, every five seconds during femtosecond procedure and after the removal of the suction ring from the eye.Results: Nine porcine eyes were used in this study. Basal IOP before suction was 5.67 ± 2.39 mmHg, rising to 20.33 ± 4.18 mmHg at the beginning of the suction phase (p < 0.001). During femtosecond procedure, pressure reached a value of 19.74 ± 4.31 mmHg, remaining stable during the entire process. The IOP recorded prior to removal of the suction ring was 21.00 ± 6.93 mmHg, returning to basal values in all the eyes after the suction ring was removed, with no statistical differences between basal and post-suction IOPs. Total femtosecond procedure time was 125.9 ± 15.9 s.Conclusions: Real-time IOP can be measured during surgery using a transducer connected to the anterior chamber. The results showed a significant increase in IOP during the procedure due to the pressure exerted by the suction ring but not by the effect of the femtosecond laser.

Whole vitreous humor dissection for vitreodynamic analysis.

The authors propose an effective technique to isolate whole, intact vitreous core and cortex from post mortem enucleated porcine eyes. While previous studies have shown the results of such dissections, the detailed steps have not been described, precluding researchers outside the field from replicating their methods. Other studies harvest vitreous either through aspiration, which does not maintain the vitreous structure anatomy, or through partial dissection, which only isolates the vitreous core. The proposed method isolates the whole vitreous body, with the vitreous core and cortex intact, while maintaining vitreous anatomy and structural integrity. In this method, a full thickness scleral flap in an enucleated porcine eye is first created and through this, the choroid tissue can be separated from the sclera. The scleral flap is then expanded and the choroid is completely separated from the sclera. Finally the choroid-retina tissue is peeled off the vitreous to leave an isolated intact vitreous body. The proposed vitreous dissection technique can be used to study physical properties of the vitreous humor. In particular, this method has significance for experimental studies involving drug delivery, vitreo-retinal oxygen transport, and intraocular convection.

Real-time ultra-high optical coherence tomography monitoring of optical tissue effects caused by selective retina therapy

Purpose: Selective retina therapy (SRT) has shown great promise compared to conventional retinal laser photocoagulation as it avoids collateral damage and selectively targets the retinal pigment epithelium (RPE). Its use, however, is challenging in terms of therapy monitoring and dosage because an immediate tissue reaction is not biomicroscopically discernibel. To overcome these limitations, real-time optical coherence tomography (OCT) might be useful to monitor retinal tissue during laser application. We have thus evaluated a proprietary OCT system for its capability of mapping optical changes introduced by SRT in retinal tissue. Methods: Freshly enucleated porcine eyes, covered in DMEM upon collection were utilized and a total of 175 scans from ex-vivo porcine eyes were analyzed. The porcine eyes were used as an ex-vivo model and results compared to two time-resolved OCT scans, recorded from a patient undergoing SRT treatment (SRT Vario, Medical Laser Center Lubeck). In addition to OCT, fluorescin angiography and fundus photography were performed on the patient and OCT scans were subsequently investigated for optical tissue changes linked to laser application. Results: Biomicroscopically invisible SRT lesions were detectable in OCT by changes in the RPE / Bruch's complex both in vivo and the porcine ex-vivo model. Laser application produced clearly visible optical effects such as hyperreflectivity and tissue distortion in the treated retina. Tissue effects were even discernible in time-resolved OCT imaging when no hyper-reflectivity persisted after treatment. Data from ex-vivo porcine eyes showed similar to identical optical changes while effects visible in OCT appeared to correlate with applied pulse energy, leading to an additional reflective layer when lesions became visible in indirect ophthalmoscopy. Conclusions: Our results support the hypothesis that real-time high-resolution OCT may be a promising modality to obtain additional information about the extent of tissue damage caused by SRT treatment. Data shows that our exvivo porcine model adequately reproduces the effects occurring in-vivo, and thus can be used to further investigate this promising imaging technique.

Experimental and Numerical Determination of the Local Temperature Distribution during Phacoemulsification and Comparison of Different Surgery Situations within Enucleated Porcine Eyes

Phacoemulsification, a common treatment for cataract, is accompanied by cell damage at the corneal endothelium. Thermal exposure during treatment has been considered a reason for this damage, but a thorough experimental and theoretical assessment of the local temperature distribution inside the eye had not yet been conducted. Measurements in porcine eyes and a finite-element simulation enabled such an assessment and localized the highest temperature rise very close to the probe. The results described in this study indicate that a distance of 1 mm between the probe and the endothelium should be maintained during treatment as a safety margin, especially when fluid flow is blocked. The highest measured temperature rise with surgically reasonable system settings and unblocked fluid flow was 1.11°C. The finite-element simulation described here is able to calculate the temperature rise at the endothelium and could serve as a tool for comparing arbitrary surgical situations with respect to thermal exposure of the endothelium.

Changes in lens stiffness due to capsular opacification in accommodative lens refilling

Accommodation may be restored to presbyopic lenses by refilling the lens capsular bag with a soft polymer. After this accommodative lens refilling prevention of capsular opacification is a requirement, since capsular opacification leads to a decreased clarity of the refilled lens. It has been hypothesized that capsular fibrosis causing the capsular opacification results in increased stiffness of the lens capsular bag, therewith contributing to a decrease in accommodative amplitude of the lens. However, the change in viscoelastic properties of refilled lenses due to capsular fibrosis has never been measured directly. In this study we examined natural lenses from enucleated porcine eyes and refilled lenses directly after refilling and after three months of culturing, when capsular fibrosis had developed, and determined their viscoelastic properties with a low load compression tester. Control refilled lenses were included in which capsular opacification was prevented by treatment with actinomycin D. We related lens stiffening to the degree of capsular opacification, as derived from the microscopic images taken with a confocal laser scanning microscope. Overall, the refilled lenses directly after refilling were softer than refilled lenses after three months of culturing, and refilled lenses treated with actinomycin D were softer compared with untreated refilled lenses. The degree of capsular opacification as assessed by microscopy corresponds to an increase in lens stiffness. This indicates that the viscoelastic properties of the refilled lens are influenced by capsular fibrosis and modulated by treatment of the lens epithelium. In conclusion, this study shows that the development of capsular fibrosis negatively affects the viscoelastic properties of isolated, cultured refilled lenses.

Accuracy and Reliability of the Icare PRO in Enucleated Porcine Eyes - Upright and Horizontal Positions

Purpose: To compare the accuracy and reliability of intraocular pressure (IOP) measurements in enucleated porcine eyes using the Icare PRO in the upright and horizontal positions. Methods: We designed an enucleated porcine eye model whose anterior chamber was cannulated with a 30-gauge needle, connected in parallel to a pneumatic pressure device. The reference pressure was manipulated by changing the air pressure from 70 to 10 mm Hg at 10 mm Hg intervals, and the IOP of porcine eyes was measured with the Icare PRO at each pressure. Correlation analysis, comparison using the Bland-Altman plot and Wilcoxon signed rank test, was performed to assess the accuracy of IOP measurements. Intraclass correlation coefficients were calculated to assess the intra-observer variability in the upright and horizontal positions, respectively. Results: The IOP value in both upright and horizontal positions was well correlated with the reference pressure (r = 0.992 and 0.985, respectively). The Bland-Altman plot showed good agreement between the two positions. However, all IOP values in both positions were lower than the reference pressures. The IOP values in the horizontal position were significantly lower than those in the upright position at the a reference pressure of 50 mm Hg or greater. Values of intraclass correlation coefficient ranged from 0.911 to 0.984 when measured in the upright position and from 0.707 to 0.914 in the horizontal position. Conclusions: IOP measurements of Icare PRO in porcine eyes were remarkably lower than reference pressures controlled by the pneumatic method even though they showed a good correlation with reference values. The higher was the reference pressure, the greater was the degree of underestimation of IOP measurement in both positions. This trend was more pronounced in the horizontal position, and the reliability of IOP measurements was also lower than that in the upright position. J Korean Ophthalmol Soc 2015;56(2):228-233

Fluctuation of the Intraocular Pressure during Intravitreal Injection

Purpose: To measure fluctuations of intraocular pressure (IOP) during intravitreal injection. Materials and Methods: We worked with enucleated porcine eyes. Different volumes (0.05, 0.075, 0.1, 0.2, and 0.3 ml) of balanced salt solution (BSS) were injected into the vitreous cavity, with sham injection (0) serving as a control. IOPs were measured in real time using a digital manometer connected to a 26-gauge catheter at the anterior chamber. Results: At baseline, the mean IOP was 4.1 ± 0.3 mmHg in the anterior chamber. A transient peak of high pressure was observed when the injection needle penetrated the sclera. A volume effect created a second peak, followed by a return to baseline after the following times (s) corresponding to the following injections: 4.4 ± 2.0 (control), 169.7 ± 6.2 (0.05 ml), 587.7 ± 83.9 (0.075 ml), 1419.2 ± 132.5 (0.1 ml), 2,381.3 ± 149.7 (0.2 ml), and 1,419.2 ± 390.1 (0.3 ml). Conclusions: Two peaks appeared during injection. The height of the second peak and the extent of delay in recovery were dependent upon the injection volume. These results provide baseline values of IOP fluctuations during intravitreal injection.

Two-dimensional micro-displacement measurement for laser coagulation using optical coherence tomography

To improve the reproducibility of photocoagulation, the ability to quantitatively monitor the thermal change of laser-irradiated retinal tissue is required. Recently, optical coherence tomography has enabled non-invasive and non-contact monitoring of the tissue structural changes during laser irradiation. To further improve the capability of this technique, a method is proposed to measure tissue displacement by simultaneously using Doppler phase shifts and correlation coefficients. The theoretical approach for this method is described, and its performance is experimentally confirmed and evaluated. Finally, lateral and axial displacements in the laser-irradiated retinal tissues of an enucleated porcine eye are observed. The proposed method is found to be useful for further understanding the direct thermal response of laser-irradiated retinal tissue.

Numerical model of optical coherence tomographic vibrography imaging to estimate corneal biomechanical properties.

Most techniques measuring corneal biomechanics in vivo are biased by side factors. We demonstrate the ability of optical coherence tomographic (OCT) vibrography to determine corneal material parameters, while reducing current prevalent restrictions of other techniques (such as intraocular pressure (IOP) and thickness dependency). Modal analysis was performed in a finite-element (FE) model to study the oscillation response in isolated thin corneal flaps/eye globes and to analyse the dependency of the frequency response function on: corneal elasticity, viscoelasticity, geometry (thickness and curvature), IOP and density. The model was verified experimentally in flaps from three bovine corneas and in two enucleated porcine eyes using sound excitation (100–110 dB) together with a phase-sensitive OCT to measure the frequency response function (range 50–510 Hz). Simulations showed that corneal vibration in flaps is sensitive to both, geometrical and biomechanical parameters, whereas in whole globes it is primarily sensitive to corneal biomechanical parameters only. Calculations based on the natural frequency shift revealed that flaps of the posterior cornea were 0.8 times less stiff than flaps from the anterior cornea and cross-linked corneas were 1.6 times stiffer than virgin corneas. Sensitivity analysis showed that natural vibration frequencies of whole globes were nearly independent from corneal thickness and IOP within the physiological range. OCT vibrography is a promising non-invasive technique to measure corneal elasticity without biases from corneal thickness and IOP.

Histological analysis of a cornea following experimental femtosecond laser ablation.

Corneal photorefractive surgery is currently performed by ablation of corneal stroma under the stromal flap. A stromal flap is created using a femtosecond (FS) laser or mechanical microkeratome, although the FS laser procedure is considered safer and more accurate. This review assesses and compares the use of FS laser versus mechanical microkeratome ablation for corneal stromal characteristics mainly examined by histology and cellular biological responses. Supporting data from our studies, using corneas of enucleated porcine eye globes, are included in this review. Histological analysis and experimental studies of cellular/tissue responses to FS laser irradiation should be further investigated, and the equipment used to perform these techniques should be improved.

The relationship between the temperature increase caused by phacoemulsification and the damage to the corneal endothelium

Endothelial cell damage can be found after a phacoemulsification. The reason for this cell damage is not yet known. The temperature rise inside the anterior chamber during the emulsification of the lens is considered as a potential damage mechanism. The aim of this study was to investigate the relationship between the temperature increase and the cell damage. This study was performed with 86 enucleated porcine eyes, which were divided into six groups A-F. Group A served as control group. Phacoemulsification was simulated in the groups B-E with different surgically relevant system settings. The temperature change was measured simultaneously with temperature sensors inside the anterior chamber. Inside the eyes of group F, the instruments were positioned and irrigation and aspiration were activated, but no ultrasound was applied. For all 86 corneas, the endothelial cell damage was quantified with a standardised evaluation protocol using scanning electron microscopy (SEM). A potential correlation was checked between the observed cell damage and the measured temperature rise. The highest temperature increase in group E with an obstructed aspiration line and an output power setting of 50 % was 17.77 °C. The temperature increase in group D with an output power setting of 100 % and unblocked fluid flow was significantly lower (p = 0.006). The highest temperature increase in group D was 8.89 °C. In contrast, the cells in group D were rated with a significantly lower score value than the cells in group E (p < 0.001). No significant correlation between the temperature rise and the cell damage could be obtained in due consideration of all measured data. However, an increase of the output power setting was connected with a non-linear increase of the cell loss. The temperature rise was not the main reason for the endothelial cell damage in the performed experiments. Therefore, there seems to be no causal relationship between the temperature increase inside the anterior chamber during a common phacoemulsification and the endothelial cell damage. Due to the strong dependence between the output power setting and the cell damage, the lowest output power setting should be used during surgery which ensures the emulsification of the nucleus.

Comparative study of corneal tangent elastic modulus measurement using corneal indentation device

The aim of this study is to examine the corneal tangent modulus measurement repeatability and performance of the corneal indentation device (CID). Twenty enucleated porcine eyes were measured and the eyes were pressurized using saline solution-filled manometer to 15 and 30mmHg. Corneal tangent moduli measured using the CID were compared with those measured using high precision universal testing machine (UTM). The within-subject standard deviation (Sw), repeatability (2.77×Sw), coefficient of variation (CV) (Sw/overall mean), and intraclass correlation coefficient (ICC) were determined. The mean corneal tangent moduli measured using UTM and CID were 0.094±0.030 and 0.094±0.028MPa at 15mmHg, and 0.207±0.056 and 0.207±0.055MPa at 30mmHg, respectively, with a difference less than 0.13%. The 95% limit of agreement was between −0.009 and 0.009MPa. The Sw, repeatability, CV and ICC of corneal tangent moduli measured by the CID were 0.006MPa, 0.015MPa, 4.3% and 0.993, respectively. The results showed that the corneal tangent moduli measured by the CID are repeatable and are in good agreement with the results measured by the high precision UTM.

Traumatic eye injuries as a result of blunt impact: computational issues

The detachment or tearing of the retina in the human eye as a result of a collision is a phenomenon that occurs very often. Reliable numerical simulations of eye impact can be very useful tools to understand the physical mechanisms responsible for traumatic eye injuries accompanying blunt impact. The complexity and variability of the physical and mechanical properties of the biological materials, the lack of agreement on their related experimental data as well as the unsuitability of specific numerical codes and models are only some of the difficulties when dealing with this matter. All these challenging issues must be solved to obtain accurate numerical analyses involving dynamic behavior of biological soft tissues. To this purpose, a numerical and experimental investigation of the dynamic response of the eye during an impact event was performed. Numerical simulations were performed with IMPETUS-AFEA, a new general non-linear finite element (FE) software which offers non uniform rational B-splines (NURBS) FE technology for the simulation of large deformation and fracture in materials. IMPETUS code was selected in order to solve hourglass and locking problems typical of nearly incompressible materials like eye tissues. Computational results were compared with the experimental results on fresh enucleated porcine eyes impacted with airsoft pellets.

A simple ex vivo model for teaching Descemet membrane endothelial keratoplasty.

To describe a simple ex vivo porcine model for teaching Descemet Membrane Endothelial Keratoplasty (DMEK). Twenty freshly enucleated porcine eyes were used to create a pseudo-graft from the porcine lens capsule and implant it into an intact porcine globe using the standardized 'no-touch' technique of the Netherlands Institute for Innovative Ocular Surgery (NIIOS). The DMEK pseudo-graft could be inserted, centred, unfolded and appositioned in all cases. Practicing DMEK surgery under wetlab conditions was feasible by the described simple and low-cost model. This new tool may facilitate the adaptation of DMEK by cornea surgeons.

Preservation of enucleated porcine eyes for use in a wet laboratory

To design a method to preserve enucleated porcine eyes for use in a wet laboratory. Laboratory of Experimental Ophthalmology, University Medical Center Groningen, the Netherlands. Experimental study. Porcine eyes were preserved using 15 methods including salt solutions, anterior chamber infusion fluids, tap water, mineral water, air, and topical glycerol on the cornea. The central corneal thickness (CCT) was measured by A-scan ultrasound over 3 days. Differences between increases in CCT were compared using repeated-measures multivariate analyses of variance. Also, lenses from eyes preserved in tap water were extracted and the lens epithelial cell morphology was studied. There was a significant interaction between the preservation method and CCT over 3 days (P<.001). Post hoc tests showed that the CCT in the sodium chloride (NaCl) 10.0% and tap-water groups increased significantly less than with 4 other preservation methods. However, preservation in NaCl 10.0% resulted in unusable shrunken coriaceous lenses. Addition of glycerol did not decrease the CCT. Lens epithelial cells from eyes preserved in tap water for 48 hours appeared to be intact but lost cell organization. Of the 15 tested methods to preserve porcine eyes, tap water (mineral content 1.79 mmol/L) resulted in the least corneal swelling. It is not necessary to use more expensive anterior chamber infusion fluids or other salt solutions. Neither author has a financial or proprietary interest in any material or method mentioned.