Osmolality of various viscoelastic substances: comparative study

A Multicenter Prospective Randomized Controlled Study of a New Corneal Wetting Agent During Ophthalmologic Surgery

INTRODUCTION

A multicenter prospective randomized controlled study was used to investigate the effect and safety of a new corneal wetting agent called the Corneal Surface Viscoelastic Protector (CsVisc, Success Bio-Tech Co., Ltd, China), on the corneal epithelium during ophthalmic surgery by comparison with the commercially available Cornea Protect (CP, Valeant Med Sp. zo. o. Leobendorf, Austria).

METHODS

This multicenter prospective randomized controlled study comprised patients scheduled for cataract surgery and pars plana vitrectomy. The patients were randomly assigned to receive either a new corneal wetting agent (CsVisc) or Cornea Protect (CP, Valeant Med Sp. zo. o. Leobendorf, Austria). Optical clarity during surgery, application frequency, duration of effect, diffusion time of corneal wetting agents, fluorescein staining, intraocular pressure (IOP), tear-film break-up time (TBUT), and Schirmer I test (SIT) were assessed. Adverse events were noted on the designated patient case report forms.

RESULTS

A total of 149 eyes (149 patients, mean age 62 years; range 25-80 years) were included in the study. There were 74 eyes in the control group and 75 eyes in the study group. In patients who underwent vitrectomy, the frequency of application was 1.62 ± 1.03 in the study group and 1.39 ± 0.66 in the control group, with no significant difference (P = 0.399), and the duration of effect was 19.16 ± 6.94 min in the study group and 19.06 ± 7.22 min in the control group, with no significant difference (P = 0.835). The optical clarity of the study group was not significantly different from that of the control group (P = 0.485). In patients who underwent cataract surgery, the frequency of application was 1.10 ± 0.38 in the study group and 1.07 ± 0.26 in the control group, and the difference was not significant (P = 0.950). The difference between the duration of effect in the study group (8.32 ± 2.50 min) and the control group (7.63 ± 2.52 min) was not significant (P = 0.310). The difference in optical clarity scores between the two groups was not statistically significant (P = 0.600). Among all patients in this study, the diffusion time of the corneal wetting agent was 14.97 ± 10.07 s in the control group and 11.23 ± 8.41 s in the study group, with a statistically significant difference (p = 0.008). The frequency of adverse events was 20.00% (15/75) in the study group and 14.86% (11/74) in the control group, with no statistically significant difference (P = 0.409). There were no serious adverse events related to the test medical device or causing patients to withdraw from the study.

CONCLUSIONS

The CsVisc is safe and effective in preventing intraoperative corneal epithelial damage due to corneal dryness and can be comparable to the CP. In addition, the CsVisc has a shorter diffusion time.

Corneal Edema after Cataract Surgery

This systematic review investigates the prevalence and underlying causes of corneal edema following cataract surgery employing manual phacoemulsification. A comprehensive search encompassing databases such as PubMed, Embase, ProQuest, Cochrane Library, and Scopus was conducted, focusing on variables encompassing cataract surgery and corneal edema. Two independent reviewers systematically extracted pertinent data from 103 articles, consisting of 62 theoretical studies and 41 clinical trials. These studies delved into various aspects related to corneal edema after cataract surgery, including endothelial cell loss, pachymetry measurements, visual performance, surgical techniques, supplies, medications, and assessments of endothelial and epithelial barriers. This review, encompassing an extensive analysis of 3060 records, revealed significant correlations between corneal edema and endothelial cell loss during phacoemulsification surgery. Factors such as patient age, cataract grade, and mechanical stress were identified as contributors to endothelial cell loss. Furthermore, pachymetry and optical coherence tomography emerged as valuable diagnostic tools for assessing corneal edema. In conclusion, this systematic review underscores the link between corneal edema and endothelial cell loss in manual phacoemulsification cataract surgery. It highlights the relevance of factors like patient demographics and diagnostic modalities. However, further research is essential to unravel the complexities of refractive changes and the underlying mechanisms.

Hyaluronic Acid: The Influence of Molecular Weight on Structural, Physical, Physico-Chemical, and Degradable Properties of Biopolymer

Hyaluronic acid, as a natural linear polysaccharide, has attracted researchers' attention from its initial detection and isolation from tissues in 1934 until the present day. Due to biocompatibility and a high biodegradation of hyaluronic acid, it finds wide application in bioengineering and biomedicine: from biorevitalizing skin cosmetics and endoprostheses of joint fluid to polymeric scaffolds and wound dressings. However, the main properties of aqueous polysaccharide solutions with different molecular weights are different. Moreover, the therapeutic effect of hyaluronic acid-based preparations directly depends on the molecular weight of the biopolymer. The present review collects the information about relations between the molecular weight of hyaluronic acid and its original properties. Particular emphasis is placed on the structural, physical and physico-chemical properties of hyaluronic acid in water solutions, as well as their degradability.

Corneal Hydration Control during Ex Vivo Experimentation Using Poloxamers

Purpose: The purpose of this study was to develop an effective treatment method using poloxamers to restore and maintain physiological hydration in postmortem porcine and human corneas during ex vivo experimentation, and to compare corneal inflation response with or without treatment.Materials and Methods: Corneal buttons obtained from whole globes (n = 30 porcine, n = 8 human) were treated with various concentrations of poloxamer 188 (P188, a synthetic macromolecule surfactant) for 24 hrs to identify the concentration that would return the cornea to near-physiological hydration (i.e. H = 3.2). Whole globes (n = 12 porcine, n = 16 human) were also used to monitor central corneal thickness (CCT) during deswelling treatment. Inflation testing from 5 to 30 mmHg was performed in the porcine globes and a subset of human globes to characterize the mechanical response of the cornea after treatment.Results: Physiological hydration was obtained after 24 hrs immersion in 3.25% P188 for porcine corneas and 4.25% P188 treatment for human corneas. CCT was stabilized and returned to physiological levels after 24 hrs of treatment in 3.25% P188 in porcine (891 ± 66 µm) and 4.25% P188 in human (574 ± 34 µm) whole globes. Corneal axial strains at 30 mmHg were significantly larger at physiological hydration than in swollen cornea in both porcine (-6.42%±1.50% vs. -3.64%±1.05%, p = .004) and human (-2.85%±0.09% in vs. -1.53%±0.27%, p = .031) eyes.Conclusions: Our results suggest that P188 treatment was effective in restoring and maintaining near physiological corneal hydration during ex vivo testing, and hydration appeared to significantly impact corneal inflation response in both porcine and human eyes.

Hydroxypropyl methylcellulose 2% for dry eye prevention during phacoemulsification in senile and diabetic patients

PURPOSE

To assess the effect of hydroxypropyl methylcellulose (HPMC) 2% to prevent dry eye during phacoemulsification in senile and diabetic patients.

METHODS

This prospective interventional case series comprised 60 eyes (44 patients) with age-related cataract scheduled for standardized phacoemulsification surgery. The patients were assigned to receive either balanced saline solution (BSS, 30 eyes) or HPMC 2% (30 eyes) during surgery. Preoperative and postoperative examinations (1, 3, 7 and 30 days) included measurements of automatic noninvasive tear film breakup time (NITBUT), fluorescein staining, Schirmer I test, tear meniscus height, depth and area and subjective symptoms. Intraoperative application frequency was also assessed.

RESULTS

The mean age of patients was 68.7 ± 2.3 years. The application frequency of BSS during surgery was significantly reduced in HPMC group (P = 0.001). The incidence of dry eye syndrome (DES) was significantly reduced in HPMC group in both senile and diabetic patients. Scores of subjective symptoms were significantly higher in the BSS group in 1 day (P = 0.003) and 3 days (P = 0.043) postoperatively. The first and average NITBUT were significantly higher in HPMC group in 1 day and 3 days after surgery, respectively (P = 0.012 and P = 0.024, respectively). NITBUT values did not significantly change postoperatively in the HPMC group (P > 0.05), while they were significantly lower postoperatively in the BSS group.

CONCLUSIONS

Application of HPMC 2% during phacoemulsification reduced the incidence of DES and improved patients' satisfaction in both senile and diabetic cataract patients. It was also effective in maintaining corneal hydration and was able to significantly reduce the application frequency intraoperatively.

Femtosecond laser-assisted cataract surgery without OVD: a prospective intraindividual comparison

PURPOSE

To compare femtosecond laser-assisted cataract surgery without the use of ophthalmic viscosurgical device (OVD) with standard phacoemulsification using OVD.

METHODS

This was a prospective, randomized, single-center trial of 37 patients (74 eyes) diagnosed as having significant cataract in both eyes. Randomly, one eye underwent standard phacoemulsification with OVD (the OVD group); this group acted as controls. The other eye was treated with the femtosecond laser; the subsequent manual part of the procedure was performed without OVD (non-OVD group). Time of surgery, amount of fluid used during phacoemulsification, central corneal thickness, intraocular pressure, endothelial cell count, and visual acuity were documented over the 6-month follow-up.

RESULTS

There were no major complications and no significant difference in overall surgery time (non-OVD: 375 ± 81 seconds; OVD: 362 ± 43 seconds; P = .713) and in the quantity of fluid passing through the eye (non-OVD: 187 ± 35 mL; OVD: 186 ± 27 mL; P = .952) between groups. Endothelial cell loss after 6 months was not significantly different between groups (non-OVD: -2.4%; OVD: -2.7%; P = .880). Central corneal thickness was not different at 1 week postoperatively between groups (non-OVD: 575 ± 45 µm; OVD: 573 ± 46 µm; P = .820). Three patients in the OVD group and one patient in the non-OVD group experienced intraocular pressure greater than 25 mm Hg at 1 day postoperatively. There were no significant differences in corrected distance visual acuity between groups (logMAR non-OVD: 0.024; OVD: 0.038; P = .461).

CONCLUSIONS

Femtosecond laser-assisted treatment allows the cataract surgeon to perform phacoemulsification and intraocular lens implantation without the use of OVD at no additional risk to the corneal endothelium. Furthermore, there was a tendency toward fewer increases in intraocular pressure in patients treated with the femtosecond laser.

Developments in injectable multiphasic biomaterials. The performance of microporous biphasic calcium phosphate granules and hydrogels

Calcium phosphate bioceramic granules associated with hydrosoluble polymers were developed as bone substitutes for various maxillofacial and orthopaedic applications. These injectable bone substitutes, support and regenerate bone tissue and resorb after implantation. The efficiency of these multiphasic materials is due to the osteogenic and osteoconductive properties of the microporous biphasic calcium phosphate. The associated hydrosoluble polymers are considered as carriers in order to achieve the rheological properties of injectable bone substitutes (IBS). In this study, we used 2 semi synthetic hydrosoluble polymers of polysaccharidic origin. The hydroxy propyl methyl cellulose (HPMC), with and without silane, was combined with microporous BCP granules. The presence of silane induced considerable gelation of the suspension. The 2 IBS used (without gelation, IBS1, with gelation, IBS2) were implanted in critical size femoral epiphysis defects in rabbits. No foreign body reactions were observed in either sample. However, because of the higher density from gelation, cell colonisation followed by bone tissue ingrowth was delayed over time with IBS2 compared to the IBS1 without gelation. The results showed resorption of the BCP granule and bone ingrowth at the expense of both IBS with different kinetics. This study demonstrates that the hydrogel cannot be considered merely as a carrier. The gelation process delayed cell and tissue colonisation by slow degradation of the HPMC Si, compared to the faster release of HPMC with IBS1, in turn inducing faster permeability and spaces for tissue ingrowth between the BCP granules.

The "Sandwich Technique" for Iris-fixated Phakic Intraocular Lens Implantation

PURPOSE

To describe a new technique of implantation of the Artisan/Verisyse phakic intraocular lens (PIOL).

METHODS

After PIOL insertion into the anterior chamber, a bolus of a high viscosity ophthalmic viscosurgical device (OVD) is placed over the optic, separating it widely from the endothelium.

RESULTS

The technique decreases the chance of endothelial damage during enclavation.

CONCLUSIONS

A bolus of a high viscosity OVD placed on the anterior surface of the Artisan/Verisyse PIOL may make enclavation safer.

Rheological characterisation of primary and binary interactive bioadhesive gels composed of cellulose derivatives designed as ophthalmic viscosurgical devices

In this study the formulation and rheological characterisation of novel candidate ophthalmic viscosurgical devices (OVD) based on binary interactive polymer gels is described. Primary systems containing either hydroxyethylcellulose (HEC) or sodium carboxymethylcellulose (NaCMC) or binary interactive gels composed of HEC and NaCMC were manufactured. Rheological characterisation was performed using texture profile analysis and oscillatory rheometry. All formulations exhibited pseudoplastic flow. Systems composed of HEC or HEC and NaCMC behaved as gels (G' > G") over the range of oscillatory frequencies whereas systems composed of NaCMC were primarily elastoviscous. Increasing the polymer concentration in all systems increased the compressional rheological properties (hardness, compressibility), zero frequency viscosity (derived from the Cross model) and the viscoelastic properties (G', G" and eta'). Rheological synergy was observed in the binary gels and was indicative of interaction between the parent polymers. Importantly, the range of rheological properties offered by the binary mixtures was greater than those exhibited by the primary systems. The binary systems described in this study possessed viscoelastic properties and steady-state viscosities that were similar to commercially available systems and would therefore be appropriate for the maintenance of the ocular space. The acceptable compressional rheological and pseudoplastic properties of these systems would facilitate administration into the eye using a syringe. Additionally and uniquely, the excellent adhesive properties of the binary interactive gels would suggest an ability to interact with the corneal endothelium that would offer protection during phacoemulsification. Based on the described rheological properties it is suggested that binary gels composed of mass ratios of HEC to NaCMC of either 3.6: 2.4 or 2.4: 3.6 would be acceptable as OVD and would uniquely offer duality of function.

Corneal edema and intraocular pressure after cataract surgery: randomized comparison of Healon5 and Amvisc Plus

PURPOSE

To compare the protective effect of Healon5 (sodium hyaluronate 2.3%) and Amvisc Plus (sodium hyaluronate 1.6%) against corneal edema and their association with postoperative intraocular pressure (IOP) spikes in patients having phacoemulsification and intraocular lens (IOL) implantation.

SETTING

Ophthalmology department of a general hospital.

METHODS

One hundred forty patients were randomly assigned to have surgery with Healon5 (n = 70) or Amvisc Plus (n = 70). One eye of each patient was analyzed. Data collected preoperatively included best corrected visual acuity (BCVA) and IOP. Central ultrasonic pachymetry was performed in all patients. The same ophthalmologist performed all surgeries. The IOP and central corneal thickness (CCT) were measured 1 and 4 days and 1 month after surgery. The BCVA was also assessed at 1 month.

RESULTS

There were no significant preoperative differences between the Healon5 and Amvisc Plus groups in sex, age, ocular pathology, BCVA, IOP, or CCT. Intraoperative variables were similar between groups, but it took significantly longer to remove the Healon5. Postoperatively, there were no differences between groups in the evolution of CCT or of IOP. Intraocular pressure spikes over 30 mm Hg were detected at 1 day in 7 patients in the Healon5 group and 2 patients in the Amvisc Plus group (10.0% versus 2.9%; P = .165).

CONCLUSIONS

Both OVDs were beneficial in a wide range of cataract patients. However, the results suggest a tendency toward a higher complication rate with Healon5.

Effect of ophthalmic viscosurgical devices on lens epithelial cells

PURPOSE

To investigate the morphological effects of Viscoat (sodium hyaluronate 3.0%-chondroitin sulfate 4.0%) on lens epithelial cells (LECs).

SETTING

Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, USA, and the Laboratory of Ultrastructural Morphology, Zoological Institute, University of Liège, Liège, Belgium.

METHODS

Human LECs collected via capsulorhexis were examined by light microscopy (LM) and transmission electron microscopy (TEM). Lens epithelial cells from rabbit capsulorhexis samples were studied by LM and TEM following exposure to Provisc (sodium hyaluronate 1.0%) or Viscoat ophthalmic viscoelastic device (OVD). Since Viscoat is hypertonic (340 mOsm), hypertonic, isotonic, and hypotonic solutions were compared to investigate a possible mechanism for the observed effects. The effects of Provisc and Viscoat on rabbit LECs in the intact lens were also compared.

RESULTS

Human LECs gathered via capsulorhexis following exposure to Viscoat were generally thinner than control samples and often had condensed nuclei and increased intracellular vacuolization. Rabbit capsular tissue exposed in situ to Viscoat demonstrated changes similar to those seen in humans. Cells exposed to Provisc were similar to cells in untreated controls in humans and rabbits. Corneal endothelial cells exposed to either agent were unaffected. Experiments with hypertonic and hypotonic buffers induced some of the changes noted with Viscoat, but the effects were less severe. Lens epithelial cells in intact rabbit lenses exposed to Viscoat appeared similar to LECs in the control samples.

CONCLUSIONS

Light microscopy and TEM of human lens capsule tissue suggest that Viscoat induces significant morphological changes in LECs during cataract surgery. The changes may underlie the improved visualization of these cells that has been reported during cataract surgery. Corneal endothelial cells were unaffected by exposure to Viscoat. Studies in a rabbit model suggest that the hyperosmolarity of Viscoat may play a partial role in the LEC changes.

Experimental study of viscoelastic in the prevention of corneal endothelial desiccation injury from vitreal fluid-air exchange

PURPOSE

To evaluate the usefulness of viscoelastic in protecting the corneal endothelium from desiccation injury associated with fluid-air exchange in a rabbit model.

DESIGN

Experimental study.

METHODS

Rabbit eyes undergoing pars plana lensectomy and vitrectomy were insufflated with either dry or humidified air for 20 minutes following introduction of either Opegan (sodium hyaluronate 1.0%; Santen, Osaka, Japan) or Viscoat (sodium hyaluronate 3%-chondroitin sulfate 4%; Alcon, Tokyo, Japan) into the anterior chamber. In two other groups of rabbit eyes, the same procedure was performed without using any viscoelastic agent. Corneas obtained from rabbits undergoing surgery were compared with corneas obtained from rabbits not undergoing surgery. Potential alterations in the corneal endothelium were investigated by scanning electron microscopy, by Phalloidin-FITC staining of actin and by in vitro measurements of corneal permeability for carboxyfluorescein using a diffusion chamber.

RESULTS

Scanning electron microscopy displayed less distortion of corneal endothelium with Opegan and Viscoat compared with the dry air-only exposed corneas. Using humidified air in Opegan and Viscoat coated corneas maintained the normal actin cytoskeleton during fluid-air exchange. Paracellular leakage was much less with Opegan and Viscoat use following infusion of dry air comparing to that of dry air-only group (P =.026 and P =.041). The difference was much more striking following humidified air infusion in Opegan or Viscoat coated corneas comparing to dry air-only infused corneas (P <.002 and P <.002).

CONCLUSIONS

Coating of rabbit corneal endothelium with Opegan or Viscoat before fluid-air exchange largely prevents dry air damage to the endothelium. Infusion of humidified air further protects corneal endothelium during fluid-air exchange in aphakic rabbit eyes.

Scheimpflug photography study of ophthalmic viscosurgical devices during simulated cataract surgery

PURPOSE

To evaluate by Scheimpflug photography the capacity of several commercially available ophthalmic viscosurgical devices (OVDs) to remain in the anterior chamber and maintain anterior chamber depth (ACD) during simulated cataract surgery in porcine cadaver eyes.

SETTING

Department of Preclinical Ophthalmology, Pharmacia & Upjohn AB, Uppsala, Sweden.

METHODS

Eighty eyes from newly slaughtered pigs were used. They were distributed equally among 8 OVDs: Amvisc Plus (sodium hyaluronate 1.6%), Biolon (sodium hyaluronate 1.0%), Biolon Prime (sodium hyaluronate 1.2%), Healon (sodium hyaluronate 1.0%), Healon GV (sodium hyaluronate 1.4%), Healon5 (sodium hyaluronate 2.3%), Provisc (sodium hyaluronate 1.0%), and Viscoat (sodium hyaluronate 3.0%-chondroitin sulfate 4.0%). Scheimpflug photographs were taken using a Nidek EAS-1000 instrument before surgery (control), after injection of the OVD, after continuous curvilinear capsulorhexis (CCC), and after lens extraction by phacoemulsification. Differences in the ACD with a P value less than 0.05 were considered statistically significant. The retention capacity was visually assessed.

RESULTS

Healon5 had a significantly higher capacity to maintain the ACD than the other OVDs after CCC and phacoemulsification. After injection, Healon5, Viscoat, and Biolon Prime showed similar ACD-maintaining capacities.

CONCLUSIONS

The capacity of Healon5 to maintain the ACD during cataract surgery, ie, neutralizing the vitreous pressure and stabilizing the anterior segment of the eye, was significantly higher than that of the other OVDs.

Synthesis and general properties of silated-hydroxypropyl methylcellulose in prospect of biomedical use

Synthesis of grafting silane on a hydro soluble cellulose ether (HPMC) was described. In alkaline medium, this derivate is under gel form. With a decrease of the pH, a self-hardening occurs due to the silanol condensation. For potential biomedical use, we described the silated-HPMC synthesis, the gel behavior after steam sterilization and the parameters of the silanol condensation i.e. pH, silane percentage and temperature. Minimum kinetic of the condensation was observed for pH between 5.5 and 6.5. So temperature catalyzed the reaction and the self-hardening speed was increased by silane percentage.

Transient corneal edema after phacoemulsification: comparison of 3 viscoelastic regimens

PURPOSE

To evaluate the effect of different viscoelastic substances on the grade and time course of postoperative corneal edema.

SETTING

Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå, Sweden.

METHODS

This study comprised 62 patients with otherwise healthy eyes who had routine phacoemulsification and intraocular lens (IOL) implantation. Patients were divided into 3 groups. Group 1 was given Healon GV (sodium hyaluronate 1.4%) at phacoemulsification and IOL implantation. Group 2 was given Viscoat (sodium hyaluronate 3.0%-chondroitin sulfate 4.0%) at phacoemulsification and Healon GV at IOL implantation. Group 3 was given Viscoat at phacoemulsification and Provisc (sodium hyaluronate 1.0%) at lens implantation. The central corneal thickness was measured with ultrasonic pachymetry before surgery and 5 and 24 hours, 1 week, and 1 month after surgery.

RESULTS

The mean increase in corneal thickness was significantly greater in Group 1 than in the other 2 groups 5 and 24 hours and 1 week after surgery.

CONCLUSIONS

The transient postoperative increase in central corneal thickness was greater in patients receiving Healon GV during phacoemulsification than in patients receiving Viscoat. The use of Provisc or Healon GV for IOL implantation did not affect the postoperative corneal thickness when Viscoat was used for phacoemulsification. The time course of the edema may be explained by a difference between the 2 agents in endothelial protection from ultrasonic, mechanical, or irrigation trauma.

Descemet membrane detachment after nonpenetrating filtering surgery

PURPOSE

To make surgeons performing nonpenetrating filtering surgery aware of an unusual complication namely Descemet membrane detachment.

METHODS

We retrospectively reviewed nine eyes of nine patients seen in our hospital with Descemet membrane detachment occurring after nonpenetrating filtering surgery from January 1994 to December 2000.

RESULTS

Both planar and nonplanar detachments were reported. Neither scrolls nor tears in the Descemet membrane were observed in any patient. After viscocanalostomy (four patients), the detachment was generally noticed shortly after the procedure and the cornea maintained its clarity. After deep sclerectomy with a collagen implant (five patients), it developed weeks to months postoperatively with adjacent corneal edema. Four patients had descemetopexy. None required more than one procedure. However, at the last visit, two detachments persisted although they had diminished in size: one after viscocanalostomy and conservative treatment and one after descemetopexy after deep sclerectomy with a collagen implant. To date otherwise, no signs of significant corneal damage could be observed clinically nor by specular microscopy and pachymetry.

CONCLUSIONS

The diagnosis of Descemet membrane detachment can be easily overlooked or misdiagnosed. The clinical presentation, clinical course, and pathogenesis depend on the type of nonpenetrating filtering surgery performed. Ophthalmologists should be aware of this unusual complication, which is likely to be more common after nonpenetrating filtering surgery than after trabeculectomy. A period of observation before attempting descemetopexy is recommended.