The effects of sodium hyaluronate, chondroitin sulfate, and methylcellulose on the corneal endothelium and intraocular pressure

Phacoemulsification and IOL-Implantation without Using Viscoelastics: Combined Modeling of Thermo Fluid Dynamics, Clinical Outcomes, and Endothelial Cell Density

Phacoemulsification is a widely used surgical method in cataract surgery with a high energy ultrasound source. The viscoelastic is considered to be tissue protective. The aim of this study is to investigate during surgery the impact of using viscoelastic versus no viscoelastic on clinical outcomes, potential complications and effect on endothelial cell density. The study group included 64 patients, who were subjected to phacoemulsification using balanced salt solution (BSS). Control group consisted of 62 patients, who underwent phacoemulsification using Hyaloronic acid 1% Healon 1%. Student’s t-test was applied for statistical analysis. The simulations of temperature changes during phacoemulsification were performed by COMSOL Multiphysics software. In the BSS group, a mean endothelial cell loss (ECL) of 4.5% was measured one month postoperatively, while in the Healon group ECL was 5.3%. Data analysis showed no significant difference in ECL between the groups (Student’s t-test, p = 0.8). No significant difference was observed in endothelial cell morphology and IOP between the two groups pre- and postoperatively (all p > 0.05). The modeling of thermo fluid dynamics showed that the heating of the cornea is slightly less when Healon was used as irrigation fluid. The phacoemulsification technique can be performed by an experienced surgeon with viscoelastics or continuous anterior chamber (AC) irrigation on the same level of safety regarding endothelial cell damage, providing equally satisfying clinical outcomes.

Chemically-Boosted Corneal Cross-Linking for the Treatment of Keratoconus through a Riboflavin 0.25% Optimized Solution with High Superoxide Anion Release

The purpose of this study was to evaluate the effectiveness and safety of a novel buffered riboflavin solution approved for corneal cross-linking (CXL) in progressive keratoconus and secondary corneal ectasia. Following the in vivo preclinical study performed on New Zealand rabbits comparing the novel 0.25% riboflavin solution (Safecross^®) containing 1% hydroxypropyl methylcellulose (HPMC) with a 0.1% riboflavin solution containing 0.10% EDTA, accelerated epithelium-off CXL was performed on 10 patients (10 eyes treated, with the contralateral eye used as control) through UV-A at a power setting of 9 mW/cm² with a total dose of 5.4 J/cm². Re-epithelialization was evaluated in the postoperative 7 days by fluorescein dye test at biomicroscopy; endothelial cell count and morphology (ECD) were analyzed by specular microscopy at the 1st and 6th month of follow-up and demarcation line depth (DLD) measured by anterior segment optical coherence tomography (AS-OCT) one month after the treatment. We observed complete re-epithelization in all eyes between 72 and 96 h after surgery (88 h on average). ECD and morphology remained unchanged in all eyes. DLD was detected at a mean depth of 362 ± 50 µm, 20% over solutions with equivalent dosage. SafeCross^® riboflavin solution chemically-boosted corneal cross-linking seems to optimize CXL oxidative reaction by higher superoxide anion release, improving DLD by a factor of 20%, without adverse events for corneal endothelium.

Methods to Induce Chronic Ocular Hypertension: Reliable Rodent Models as a Platform for Cell Transplantation and Other Therapies

Glaucoma, a form of progressive optic neuropathy, is the second leading cause of blindness worldwide. Being a prominent disease affecting vision, substantial efforts are being made to better understand glaucoma pathogenesis and to develop novel treatment options including neuroprotective and neuroregenerative approaches. Cell transplantation has the potential to play a neuroprotective and/or neuroregenerative role for various ocular cell types (e.g., retinal cells, trabecular meshwork). Notably, glaucoma is often associated with elevated intraocular pressure, and over the past 2 decades, several rodent models of chronic ocular hypertension (COH) have been developed that reflect these changes in pressure. However, the underlying pathophysiology of glaucoma in these models and how they compare to the human condition remains unclear. This limitation is the primary barrier for using rodent models to develop novel therapies to manage glaucoma and glaucoma-related blindness. Here, we review the current techniques used to induce COH-related glaucoma in various rodent models, focusing on the strengths and weaknesses of the each, in order to provide a more complete understanding of how these models can be best utilized. To so do, we have separated them based on the target tissue (pre-trabecular, trabecular, and post-trabecular) in order to provide the reader with an encompassing reference describing the most appropriate rodent COH models for their research. We begin with an initial overview of the current use of these models in the evaluation of cell transplantation therapies.

Comparison of the Effect of Sodium Hyaluronate (Ophthalin®) and Hydroxypropylmethylcellulose (HPMC-Ophtal®) on Corneal Endothelium, Central Corneal Thickness, and Intraocular Pressure after Phacoemulsification

PURPOSE

To prospectively evaluate the effects of 2% hydroxypropyl-methylcellulose (HPMC-Ophtal) and sodium hyaluronate 1% (Ophthalin) on intraocular pressure, corneal thickness, and endothelial cell loss in small incision cataract surgery with implant.

METHODS

A total of 110 patients undergoing routine phacoemulsification with implant received either 2% hydroxypropyl methylcellulose or sodium hyaluronate 1% as ophthalmic viscosurgical device. Pre- and postoperative slitlamp examination, intraocular pressure measurement (preoperatively and at 1-4 hours, 1 day, and 7 days postoperatively), ultrasonic pachymetry (preoperatively and at 1 week, 4-6 weeks, and 12 weeks post operatively), and corneal endothelial cell count (preoperatively and 12 weeks postoperatively) were performed. Data were analyzed using two-way analysis of variance.

RESULTS

All measurements were comparable between the two groups preoperatively. Intraocular pressure was significantly lower in the Ophthalin group at 1 day post operatively, while no significant difference was found between the two groups on the 1-4 hours and 7 days examination. The central corneal thickness was not significantly different between the two groups at any postoperative visit . However, the mean cell density demonstrated a significant fall of 11.76% for Ophthalin and 4.27% for HPMC-Ophtal at 12 weeks post-operatively, the difference between the two being significant (p=0.009).

CONCLUSIONS

2% Hydroxypropyl methylcellulose, compared with sodium hyaluronate 1%, is superior in protecting the corneal endothelial cells, has the same effect on central corneal thickness, and is associated with slightly higher intraocular pressure 1 day post operatively. It compares favorably with sodium hyaluronate 1% and can be used as an effective and cheaper alternative in routine small incision cataract surgery with implant.

1: Final Report on the Safety Assessment of Hydroxyethylcellulose, Hydroxypropylcellulose, Methylcellulose, Hydroxypropyl Methylcellulose, and Cellulose Gum

Hydroxyethylcellulose, Hydroxypropylcellulose, Methylcellulose, Hydroxypropyl Methylcellulose, and Cellulose Gum are modified cellulose polymers that are used in cosmetic products at concentrations up to 10%. The cellulose derivatives pass essentially unchanged through the gastrointestinal tract following oral administration. They are practically nontoxic when administered by inhalation or by oral, intraperitoneal, subcutaneous, or dermal routes. Subchronic and chronic oral studies indicate that the cellulose derivatives are nontoxic when administered to laboratory animals. No significant teratogenic or reproductive effects have been demonstrated. Ocular and dermal irritation studies show that the cellulose derivatives are, at most, minimally irritating to rabbit eyes and nonirritating to slightly irritating to rabbit skin when tested at concentrations up to 100%. No mutagenic activity of theseingredients was demonstrated. The cellulose derivatives at concentrations up to 100% were nonirritating to mildly irritating, nonsensitizing, and nonphotosensitizing when evaluated in clinical studies. It is concluded that theingredients reviewed are safe as cosmeticingredients in the present practices of use and concentration.

Efficacy of brimonidine 0.2% in controlling acute postoperative intraocular pressure elevation after phacoemulsification

PURPOSE

To determine the efficacy of brimonidine tartrate 0.2% drops given 2 times a day in reducing intraocular pressure (IOP) spikes during the first 24 hours after phacoemulsification cataract surgery.

SETTING

Department of Ophthalmology, General Hospital of Patras Agios Andreas, Patras, Greece.

METHODS

In this prospective double-blind placebo-controlled study, 1 eye of 40 consecutive normotensive cataract patients having small-incision cataract surgery was randomized into 1 of 2 treatment arms. Twenty patients received a placebo (artificial tears) and 20 patients received brimonidine tartrate 0.2% drops 2 times a day the day before and the day of surgery. Diurnal IOP variation was the primary efficacy variable; IOP was measured at baseline, before surgery, and 4, 6, 12, and 24 hours postoperatively.

RESULTS

The placebo group had higher IOPs at every time point after surgery. Peak elevation of IOP occurred 6 hours after surgery. The mean IOP in the placebo group (27.71 mm Hg +/- 3.75 [SD]) was statistically significantly higher than in the brimonidine group (21.45 +/- 1.32 mm Hg) (P<.001). A major IOP rise (>/=20 mm Hg above baseline IOP) occurred in 1 patient (5%) in the placebo group who required emergency hypotensive therapy. Twenty-four hours after surgery, 11 eyes (55%) in the brimonidine group and 4 eyes (20%) in the placebo group had an IOP lower than baseline.

CONCLUSION

Prophylactic treatment with brimonidine tartrate 0.2% 2 times a day for 2 days was effective in reducing IOP peaks throughout the first 24 hours after phacoemulsification surgery.

Evaluation of corneal damage by combined phacoemulsification and passive efflux of silicone oil in vitrectomized eyes

PURPOSE

To evaluate the effect on the corneal endothelium of phacoemulsification combined with passive silicone oil removal and intraocular lens (IOL) implantation under topical anesthesia after pars plana vitrectomy.

SETTING

Department of Ophthalmology and Otolaryngology, University of Bari, Bari, Italy.

METHODS

This retrospective study evaluated the corneal endothelium in 17 consecutive patients (17 eyes) who had phacoemulsification with transpupillary passive silicone oil washout (1300 centistokes) through a posterior capsulorhexis and single clear corneal incision and foldable acrylic IOL implantation. The findings were compared with those in a control group of 17 patients (17 eyes) who had phacoemulsification with acrylic IOL implantation through a single clear corneal incision. All procedures were performed by the same surgeon using topical anesthesia. The preoperative and postoperative endothelial cell densities, coefficient of variation (CV), and percentage of hexagonal cells at the corneal center and peripheral temporal position, evaluated by noncontact specular microscopy, were compared between the 2 groups. The central corneal thickness and occurrence of keratopathy were also noted.

RESULTS

The mean phacoemulsification and total ultrasound times did not differ significantly between the 2 groups. At 6 months, the mean endothelial cell loss was 284.50 cell/mm(2) +/- 462.3 (SD) (11.2%) in the study group and 200.15 +/- 117.9 cell/mm(2) (8.3%) in the control group (P=.87, unpaired t test). There were no significant between-group differences in the increase in the mean CV and the percentage of hexagonal cells. The mean pachymetry remained at preoperative values, with no difference between groups. Keratopathy was not observed in any patient.

CONCLUSIONS

Passive silicone oil efflux caused significant endothelial cell loss and changes in endothelial morphology. Nevertheless, these modifications were well tolerated and minimally different from the results of trauma caused by standard phacoemulsification with posterior chamber IOL implantation.

Intraocular pressure development after cataract surgery: a prospective study in 50 dogs (1998-2000)

OBJECTIVE

To study the course of intraocular pressure (IOP) after cataract surgery in 50 dogs.

DESIGN

Prospective study.

ANIMALS

Fifty dogs without preoperative ocular hypertension were selected for cataract surgery.

METHODS

All dogs underwent cataract surgery: 25 by manual extracapsular extraction and 25 by phacoemulsification. For each dog, intraocular pressure was measured before surgery, and 1, 3, 5, 18 h, 1 week and 1 month post surgery.

RESULTS

No significant difference of mean intraocular pressure between the two surgical methods was observed for each time measurement. Nine dogs had postoperative hypertension (IOP > 25 mmHg) during the first 5 hours post surgery. Incidence of postoperative hypertension was not significantly different with manual extracapsular extraction (16%) vs. phacoemulsification (20%). A decrease of mean IOP was observed 1 h after surgery (8.49 mmHg vs. 10.91 mmHg), then an increase 3 and 5 h post surgery (12.3 and 13.32 mmHg, respectively). At 18 h, 1 week and 1 month post surgery, mean IOP decreased. Mean IOP was 10.38, 10.38 and 8.84 mmHg, respectively.

CONCLUSION

In this study incidence of POH is not high. However, a follow-up of IOP in the first hours after cataract surgery is required to avoid complications of the retina and optic nerve and to administer hypotensive treatment if necessary.

Influence of viscoelastic substances used in cataract surgery on corneal metabolism and endothelial morphology: comparison of Healon and Viscoat

PURPOSE

To evaluate the influence of cohesive and dispersive ophthalmic viscosurgical devices (OVDs) on endothelial morphology and corneal metabolism during cataract surgery.

SETTING

Department of Ophthalmology, University of Vienna Medical School, Vienna, Austria.

METHODS

In this prospective randomized blind study, 50 eyes of 43 patients were randomized into 2 groups before surgery. Phacoemulsification with implantation of a posterior chamber intraocular lens was performed in all patients. In half the patients, sodium hyaluronate 1% (Healon) was used as the OVD and in the other half, sodium hyaluronate 3%-chondroitin sulfate 4% (Viscoat). Corneal metabolism was evaluated by fluorophotometric measurement of corneal autofluorescence. The corneal fluorescence values were corrected for interference by fluorescence of the ocular lens. Specular microscopy (Noncon Robo SP800, Canon) was used to evaluate the endothelial cell density, coefficient of variation, and percentage of hexagonal cells. Examinations were performed preoperatively and 3 days, 1 and 4 weeks, and 3 months postoperatively.

RESULTS

There were no significant changes between preoperative and postoperative endothelial cell density measurements in either group (P =.1717). The percentage of hexagonal cells was similar (P =.3489); however, there was a slightly increasing tendency toward polymorphism in both groups. Corneal autofluorescence decreased 3 days after surgery, increased after 1 week, and decreased again subsequently in both groups. There was no significant difference in the influence on corneal metabolism between the 2 OVDs (P =.9899).

CONCLUSIONS

There was no significant difference between Healon and Viscoat. Thus, this study did not confirm an advantage of either for endothelial protection of healthy corneas.

Intraocular pressure rise after small incision cataract surgery: a randomised intraindividual comparison of two dispersive viscoelastic agents

AIM

To evaluate the effects of the dispersive viscoelastic agents Ocucoat (hydroxypropyl methylcellulose 2%) and Viscoat (sodium chondroitin sulphate 4%-sodium hyaluronate 3%) on postoperative intraocular pressure (IOP) after bilateral small incision cataract surgery.

METHODS

This prospective, randomised study comprised 80 eyes of 40 consecutive patients with age related cataract in both eyes scheduled for bilateral small incision cataract surgery. The patients were randomly assigned to receive Ocucoat or Viscoat during cataract surgery of the first eye. The second eye was operated later and received the other viscoelastic agent. Cataract surgery was performed with a temporal 3.2 mm sutureless posterior limbal incision, phacoemulsification, and implantation of a foldable silicone intraocular lens. The IOP was measured preoperatively as well as 6 hours, 20-24 hours, and 1 week postoperatively.

RESULTS

At 6 hours after surgery the mean IOP increased by 4.6 (SD 5.1) mm Hg in the Ocucoat group (p<0.001) and by 8.6 (8.1) mm Hg in the Viscoat group (p<0.001). The increase was significantly higher in the Viscoat group than in the Ocucoat group (p=0.004). Intraocular pressure spikes of 30 mm Hg or more occurred in two eyes in the Ocucoat and in nine eyes in the Viscoat group (p=0.023); 20-24 hours and 1 week postoperatively the mean IOP was not statistically different.

CONCLUSION

These findings indicate that Viscoat causes a significantly higher IOP increase and significantly more IOP spikes than Ocucoat in the early period after small incision cataract surgery.

Corneal thickness and visual acuity after phacoemulsification with 3 viscoelastic materials

PURPOSE

To determine whether differences exist in visual acuity and corneal thickness after phacoemulsification using various viscoelastic substances.

SETTING

Phillips Eye Institute, Minneapolis, Minnesota, USA.

METHODS

Fifty patients having routine phacoemulsification cataract extraction and intraocular lens implantation by a single surgeon using the same technique were randomly assigned to receive intraoperative administration of 1 of 3 viscoelastic substances: Amvisc Plus(R) (sodium hyaluronate 1.6%), OcuCoat(R) (hydroxypropyl methylcellulose 2%), or Viscoat(R) (chondroitin sulfate 4%-sodium hyaluronate 3%). Visual acuity and corneal thickness on the first postoperative day were compared between groups.

RESULTS

Patients with a best corrected visual acuity (BCVA) of 20/40 or better 1 day postoperatively had significantly thinner corneas (596 microm) than those with a BCVA worse than 20/40 (639 microm). There were no differences in postoperative BCVA or percentage increase in central corneal pachymetry among the 3 viscoelastic groups.

CONCLUSION

Viscoat, Amvisc Plus, and OcuCoat were comparable in their ability to produce clear corneas and good vision after routine phacoemulsification.

A viscous bioerodible poly(ortho ester) as a new biomaterial for intraocular application

The biocompatibility of a viscous, hydrophobic, bioerodible poly(ortho ester) (POE) intended for intraocular application was investigated. POE was evaluated as a blank carrier and as containing modulators of degradation. Each formulation was injected intracamerally and intravitreally in rabbit eyes, and clinical and histological examinations were performed postoperatively for 2 weeks. In the case of intracameral injections, polymer biocompatibility appeared to depend on the amount injected in the anterior chamber. When 50 microL was administered, the polymer degraded within 2 weeks, and clinical observations showed good biocompatibility of POE with no toxicity to the ocular tissues or increase in intraocular pressure. The injection of a larger volume, 100 microL, of POE, appeared inappropriate because of direct contact of polymeric material with the corneal endothelium, and triggered reversible edema and inflammation in the anterior chamber of the eye that regressed after a few days. After intravitreal administration, POE was well tolerated and no inflammatory reaction developed during the observation period. The polymer degraded slowly, appearing as a round whitish bubble in the vitreous cavity. The presence of modulators of degradation both improved POE biocompatibility and prolonged polymer lifetime in the eye. POE appears to be a promising biomaterial for clinical intraocular application.

Effects of hyaluronan viscous materials on cell membrane electrical properties

Hyaluronan [hyaluronic acid (HA)] has been implicated in various cellular processes such as proliferation, adhesion, migration, and differentiation. The secondary and tertiary structures of HA give it very important and unique viscoelastic properties. HA-composed materials are currently used intraocularly during ophthalmological surgery to facilitate surgical procedures and prevent tissue damage. To examine the effects of three viscous biomaterials composed of hyaluronan (Healon, IAL, and Biolon) used in ophthalmological surgery, the membrane electrical properties of the erythroleukemic K562 cell line exposed to these materials were investigated. Membrane conductivity, membrane permittivity, and the conductivity of the cytosol were evaluated using dielectric relaxation measurements in the radiofrequency range and fitting the experimental results to the general equations of the Maxwell-Wagner effect. The results demonstrate that while membrane permittivity and the conductivity of the cytosol are not significantly altered, the membrane conductivity of K562 cells exposed to all three biomaterials increases substantially and in a time-dependent manner with respect to untreated cells. These observations seem to indicate that hyaluronan perturbs ionic transport while it does not vary the type, quantity, or distribution of membrane components. In addition, the variations induced by these substances on the cell membrane are not dependent upon the molecular weight or on the biological origin of hyaluronan. These results may aid in elucidating the mechanisms involved in hyaluronan/cell membrane interaction and thus may provide a deeper understanding of the complications related to their use in ophthalmological surgery.

The effect of phacoemulsification on aqueous outflow facility

OBJECTIVE

Although control of intraocular pressure (IOP) after cataract extraction may be of critical importance, little is known regarding changes in facility of outflow in the early postoperative period. The effect of phacoemulsification and conjunctival peritomy size on the coefficient of aqueous outflow facility (C) and IOP was studied.

DESIGN

Participants were assigned randomly to one of two treatment groups.

PARTICIPANTS

Seventy-four patients with cataract and without evidence of glaucoma were studied.

INTERVENTION

Patients were randomized to receive either single- or two-quadrant conjunctival peritomy and phacoemulsification.

MAIN OUTCOME MEASURES

Tonometry and tonography were assessed before surgery and at 1 day, 1 week, 6 weeks, and 1 year after surgery by a masked observer.

RESULTS

Fifty patients with a mean of 11.4 months' (range, 10-13 months) follow-up were analyzed. Patients with reduced preoperative facility of outflow (as defined by C < or = 0.28 microliter/min/mmHg) showed a significant improvement from a mean preoperative value of 0.24 +/- 0.04 microliter/min/mmHg to 0.41 +/- 0.22 microliter/min/mmHg at 1 year (P = 0.002, N = 19). Among all patients, there was no significant change between mean preoperative C and last follow-up (0.39 +/- 0.23 vs. 0.46 +/- 0.38 microliter/min/mmHg, not significant [ns], N = 50). Furthermore, there was no significant change between mean preoperative and final IOP (23.7 +/- 4.1 vs. 23.3 +/- 3.9 mmHg, ns, N = 50). There was a significant elevation of mean IOP on postoperative day 1 to 27 +/- 6.2 mmHg (P = 0.001, N = 50). Patients with IOP elevations greater than 8 mmHg on postoperative day 1 had significantly elevated IOP at 1 year compared to preoperative values (P = 0.02, N = 12). There were no significant differences detected regarding C or IOP between single- or two-quadrant peritomy groups.

CONCLUSIONS

Outflow facility improves after phacoemulsification in patients with a reduced preoperative coefficient of aqueous outflow. Postoperative day 1 IOP is significantly elevated after phacoemulsification. Conjunctival peritomy size does not appear to play a role in aqueous outflow facility or IOP after surgery.

Effect of trabecular aspiration on early intraocular pressure rise after cataract surgery

PURPOSE

To evaluate the efficacy of a new trabecular aspiration technique on intraocular pressure (IOP) immediately after cataract surgery.

SETTING

University Eye Hospital of Cologne, Germany.

METHODS

This prospective, double-masked study comprised 48 of 100 patients having extracapsular cataract extraction (ECCE) who were randomly assigned to a study group. In these patients, 180 degrees of the inferior circumference of the chamber angle was treated with negative suction pressure ranging between 100 and 200 mm Hg. The other 52 patients served as a control group. Intraocular pressure was measured preoperatively and early (5 to 7 hours) and late (12 to 48 hours) postoperatively.

RESULTS

There was a significant mean increase in IOP from the preoperative to early postoperative period in both the control group (20.8 mm Hg) and the treatment group (7.4 mm Hg). There was no significant difference between preoperative and late postoperative pressures in either group. A one-way analysis of covariance of the changes in pressure from the preoperative to early postoperative period showed significantly less increase (P = .0041) in the aspiration than in the control group.

CONCLUSION

Trabecular aspiration was effective in reducing the amount of IOP increase in the immediate period after ECCE.

Corneal endothelial protection by different viscoelastics during phacoemulsification

PURPOSE

To evaluate corneal endothelium morphology and function after phacoemulsification using different viscoelastics.

SETTING

Eye Clinic, University of Trieste, Italy.

METHODS

This prospective, randomized study included results of preoperative and postoperative (7, 30, and 90 days) examinations of 66 patients scheduled for phacoemulsification without ocular pathology; 8 patients were excluded. Patients were randomly assigned to one of four groups based on type of viscoelastic used: 1% sodium hyaluronate (Healon); 1.4% sodium hyaluronate (Healon GV); 4% sodium chondroitin sulfate-3% sodium hyaluronate (Viscoat); 2% hydroxypropyl methylcellulose (Hymecel). Mean cell density and cell size variation coefficient were determined by specular microscopy; central corneal thickness, by ultrasonic pachymetry; and endothelial permeability coefficient and active pump function, by anterior segment fluorophotometry.

RESULTS

There were no significant differences in postoperative mean cell loss among the groups. The cell size variation coefficient was altered in all groups 7 days after surgery and was still impaired at 30 days in the Hymecel group. A significant increase in mean corneal thickness, endothelial permeability, and active pump function occurred in the Healon and Hymecel groups 7 days after surgery. These parameters were still altered 30 days after surgery in the Hymecel group. Endothelial functional alterations did not occur in the Healon GV or Viscoat group.

CONCLUSION

Viscoat and Healon GV are effective in minimizing functional damage of endothelial structure in the early medium-term postoperative period.

Effects of viscoelastics on bovine corneal endothelial cells in vitro

PURPOSE

To evaluate the possible toxic effects of sodium hyaluronate and hydroxypropyl methylcellulose on corneal endothelium.

METHODS

Cultured bovine corneal endothelial cells (BCEC) were treated with either original Healon (10 mg/ml) or Methocel (20 mg/ml) for 1 h, or with various dilutions of these substances in culture medium for up to one week. The toxicity of the viscoelastics was assessed in terms of lactate dehydrogenase (LDH) release into the supernatant and of cell density.

RESULTS

Neither Healon nor Methocel in a dilution of 2 mg/ml enhanced LDH release after 72 h incubation, when compared with the control in a confluent model. In a proliferation model neither diluted Healon nor Methocel showed apparent inhibitory or stimulatory effects on the growth of BCEC up to the highest concentration we tested. When a BCEC monolayer was covered for 1 h with either undiluted Healon or undiluted Methocel, a significant, though transient, higher LDH release was induced.

CONCLUSION

The results indicate that the diluted viscoelastics are safe for long time contact with BCEC, but undiluted they may temporarily interfere with the metabolism of the cytoplasm membranes of BCEC.

Evaluation of intraocular pressure with Healon and Healon GV in sutureless cataract surgery with foldable lens implantation

PURPOSE

To evaluate transient increases in intraocular pressure (IOP) after use of high-viscosity viscoelastic agents in cataract surgery.

SETTING

Military Hospital, Ulm, Germany.

METHODS

In a prospective, randomized study, we evaluated IOP following cataract surgery using two different viscoelastic substances (Healon, Healon GV). The viscosity of Healon GV is 10 times higher than that of Healon because of higher concentration and molecular weight. Patients having identical phacoemulsification procedures (sutureless clear corneal tunnel incision with foldable silicone lens implantation) (N = 60) and identical viscoelastic removal were assigned to groups of 15 based on viscoelastic used and removal time (20 or 40 seconds). Intraocular pressure was measured preoperatively and at 6, 24, 36, and 48 hours and 1 month postoperatively.

RESULTS

The highest mean IOP elevations in both viscoelastic groups were obtained at 24 hours postoperatively (2.9 mm Hg +/- 4.3 [SD] with Healon and 3.3 +/- 6.3 mm Hg with Healon GV). There were no statistically significant differences between the two viscoelastics and the two removal times during the entire follow-up period (unpaired t-test), but standard deviations were higher in the Healon GV groups at 6 and 24 hours. Two patients in the Healon groups and three in the Healon GV groups required medical treatment for IOP within the first 24 postoperative hours; however, all five patients had an IOP lower than 22 mm Hg on the second postoperative day.

CONCLUSIONS

Based on postoperative IOP, both viscoelastics can be equally well removed from the anterior chamber. Incidence of high IOP using high-viscosity hyaluronic acid is minimized by the described removal technique.

Effect of cataract surgery on aqueous turnover and blood-aqueous barrier

We evaluated changes in aqueous outflow and blood-aqueous barrier (BAB) disruption after cataract surgery in two randomly selected groups of eyes. In one group, a high-viscosity viscoelastic was used for intraocular lens (IOL) implantation; in the other, a low-viscosity viscoelastic. Fluorophotometry was used to evaluate aqueous humor dynamics five to seven hours after IOL implantation. Aqueous outflow after IOL implantation in operated eyes was nearly twice that in the fellow eyes, which served as controls. Mean protein concentration in the anterior chamber was also elevated in operated eyes. However, postoperative aqueous outflow did not differ significantly between the two groups. The substantial increase in aqueous outflow observed postoperatively and the increase in aqueous humor protein concentration were closely related to BAB disruption. These results suggest that BAB disruption may be a main cause of the transient high intraocular pressure observed after IOL implantation in both groups.

Comparative clinical trial of AMO Vitrax and Healon use in extracapsular cataract extraction

This randomized, single-masked, multicenter clinical trial, comprising 95 patients enrolled at five sites, evaluated the performance of AMO Vitrax and Healon viscoelastic materials during cataract surgery. Patients were examined preoperatively and at one day, four days, one month, and three months postoperatively. The following measurements were recorded and analyzed: percentage of endothelial cell loss from preoperative to three months postoperative; change in intraocular pressure (IOP) from preoperative to 24 hours postoperatively; postoperative corrected visual acuity; subjective assessment of ability of viscoelastic to create and maintain tissue space; intraocular transparency; ease of evacuation. Three months postoperatively, endothelial cell loss was 4.9% (+/- 8.3%) for the AMO Vitrax group and 6.3% (+/- 10.5%) for the Healon group. One day postoperatively, IOP decreased by 1.6 mm Hg and increased by +1.1 mm Hg, respectively. Postoperative visual acuities were similar between the two groups at three months. Subjective assessment of transparency was higher for Healon. Assessment of tissue space maintenance was similar between the two materials. Healon was rated as slightly easier to evacuate.

Viscoelastic-related glaucomas

The routine surgical use of viscoelastic substances has revolutionized many anterior segment procedures. All of the currently available agents may be responsible for causing or exacerbating a transient, but occasionally significant, postoperative IOP elevation. In spite of differences in physical properties such as molecular weight, concentration, and viscosity, none of the various viscoelastics has consistently shown a decreased likelihood of producing ocular hypertension. Moreover, any newly introduced product must be evaluated carefully for this potential complication. Lavage of viscomaterial from the anterior chamber and administration of ocular antihypertensives may be helpful in averting or controlling the increased IOP. The surgeon should be cognizant of any pre-existing optic nerve damage and adjust the aggressiveness of postoperative glaucoma therapy accordingly. In the future, the development of new substances or simultaneous use of degrading enzymes may reduce or eliminate the incidence of viscoelastic-induced ocular hypertension.

Pupillary block during cataract surgery

Sudden phakic pupillary block occurred immediately upon cortical cleaving hydrodissection during cataract surgery in two patients. We believe this unique complication is related to the recent introduction of viscoelastics with properties that enhance the maintenance of the anterior chamber during capsulorhexis. We postulate that the cause of the block was a combination of O-ring capsulocortical and iridocapsular seals that tamponade hydrodissection fluid posteriorly. Additional precipitating factors were diabetes, poorly dilating pupils, and increased vitreous pressure, which may have contributed to the sudden and irreversible nature of this block. If this complication is not recognized, an aqueous misdirection syndrome may ensue, requiring pars plana vitrectomy. Immediate mechanical breakage of the pupillary and capsular block, resulting in an immediate decrease in intraocular pressure from greater than 70 mm Hg, may cause severe retinal vascular damage. These cases stress the importance of mechanical pupil dilation to prevent this serious complication of cataract surgery.

Phacoemulsification with aspirated or retained Viscoat

Endothelial cell counts, morphology, and 24-hour postoperative intraocular pressure (IOP) changes were measured in 55 consecutive patients (60 eyes) who had uncomplicated phacoemulsification and posterior chamber lens implantation with either aspirated (30 eyes) or retained (30 eyes) Viscoat (sodium chondroitin sulfate-sodium hyaluronate). The surgical technique was standardized in all cases. Endothelial cell loss was almost identical in the aspirated and in the retained groups (8.8% and 8.7%). Postoperative pleomorphism was significantly less in the retained Viscoat group than in the aspirated group, suggesting a possible protective effect of the retained viscoelastic. Corneal thickness increased significantly in the retained Viscoat group, but this was not significant clinically. The retained Viscoat group had more patients with a postoperative IOP greater than 30 mm Hg and a greater mean increase in postoperative IOP, although the difference between the groups was not significant. The IOP changes may have been caused by blockage of the trabecular meshwork by the retained Viscoat. The results suggest that Viscoat can be retained after cataract surgery if the surgeon is prepared for a greater 24-hour postoperative increase in IOP.

Corneal endothelial and intraocular pressure changes after phacoemulsification with Amvisc Plus and Viscoat

A prospective, randomized, observer-marked study was conducted to compare corneal endothelial and intraocular pressure (IOP) changes after cataract surgery with the viscoelastic agents Amvisc Plus and Viscoat. Forty-nine patients (50 eyes) who had uncomplicated phacoemulsification and implantation of a posterior chamber intraocular lens were randomly assigned to either Amvisc Plus (25 eyes) or Viscoat (25 eyes) groups. Surgical technique was rigidly standardized in all cases. No significant difference in endothelial parameters or postoperative IOPs measured at 24 hours, one week, and two months was detected by analysis of variance between the Amvisc Plus and the Viscoat groups. Visualization was difficult with Viscoat because of its tendency to retain bubbles. Phacoemulsification energy was related to a loss of endothelial density, regardless of the viscoelastic used. The postoperative beta blocker may have contributed to the lower average postoperative IOP than has been reported.

Intraocular pressure after extracapsular cataract extraction with implantation of posterior chamber lenses

To determine factors which influence postoperative intraocular pressure (IOP) we retrospectively reviewed changes in pressure during the first postoperative week in 633 consecutive eyes undergoing extracapsular cataract extraction (ECCE) with implantation of a posterior chamber lens. The material was restricted to four surgeons and two types of lenses. IOP was measured preoperatively, one day and one week after surgery. Glaucomatous eyes (n = 113) as well as exfoliative non-glaucomatous eyes (n = 79) had a higher mean IOP (27.8 and 26.1 mmHg) the first postoperative day compared to 'simple' cataract eyes (20.1 mmHg). After one week mean IOP in glaucomatous eyes still remained elevated while exfoliative non-glaucomatous eyes had regained preoperative values. Mean IOP on the first postoperative day (18.8, 24.5, 23.1 and 13.2 mmHg respectively) was also dependent on surgeon. To some extent the IOP could be correlated to tightness of suturing as estimated by keratometry. Only one surgeon had significant difference between irrigated and non-irrigated visco-elastic substance. Postoperative pressure was not only dependent on the status of the patient's eye, but factors for the individual surgeons seemed to be as important.

Healon GV in extracapsular cataract extraction with intraocular lens implantation

A randomized masked study was performed to compare Healon GV, a new higher molecular weight sodium hyaluronate viscoelastic, with Healon in extracapsular cataract surgery with posterior chamber intraocular lens insertion. Seventy patients were randomly divided into two groups. Postoperative intraocular pressures, pachymetry, endothelial cell counts and morphology, amount of viscoelastic and irrigating solution used, difficulty of surgery, and postoperative flare and cells were measured. Postoperative pressures were not significantly different between the Healon and Healon GV treatment groups, except at the eight-hour observation period, when the pressure was higher in the Healon GV group (P = .02). There was a significant (P = .002) reduction in the amount of viscoelastic required in the Healon GV group. Cell counts and morphology were not significantly different between the groups. Other parameters showed no significant difference. Clinically, Healon GV handled like Healon during instillation into the anterior chamber and aspiration at the end of the case. It did, however, appear to be much more effective at maintaining the anterior chamber, as demonstrated in the smaller amount of viscoelastic required.

Effect of topical apraclonidine on the frequency of intraocular pressure elevations after combined extracapsular cataract extraction and trabeculectomy

PURPOSE

A trabeculectomy is frequently combined with extracapsular cataract surgery to minimize the risks of further optic nerve damage associated with intraocular pressure (IOP) elevations after cataract surgery in eyes with glaucoma. Acute IOP elevations still occur after this combined surgery. The author evaluated the efficacy of 1% topical apraclonidine, a relatively selective alpha 2 agonist, in minimizing this complication.

METHODS

A prospective, randomized, double-masked study compared topical 1% apraclonidine with placebo. All eyes underwent otherwise uncomplicated combined trabeculectomy and extracapsular cataract surgery. They received the appropriate study drug before, immediately after, and 12 hours after surgery. Intraocular pressures were measured 24 hours and 1, 2, and 4 weeks after surgery.

RESULTS

One hundred nine eyes (of 109 patients) underwent combined surgery. Fifty-nine received placebo. Preoperative mean IOPs were 22.5 +/- 4.2 mmHg for eyes treated with placebo and 24.0 +/- 7.7 mmHg for eyes treated with apraclonidine. Twenty-four hours after surgery, mean IOPs were 23.1 +/- 17.4 mmHg for placebo-treated eyes and 11.6 +/- 11.3 mmHg for apraclonidine-treated eyes (P < 0.001). Twenty-four hours after surgery, 12 (20%) placebo-treated eyes and 1 (2%) apraclonidine-treated eye had IOPs greater than 40 mmHg (P < 0.005).

CONCLUSION

Apraclonidine effectively decreased large IOP elevations in glaucomatous eyes undergoing trabeculectomy combined with extracapsular cataract surgery.

Analysis of the short-term effect of two viscoelastic agents on the intraocular pressure after extracapsular cataract extraction. Sodium hyaluronate 1% vs hydroxypropyl methylcellulose 2%

We conducted a study to evaluate the shortterm effect on intraocular pressure (IOP) following extracapsular cataract extraction using either sodium hyaluronate 1% or hydroxypropyl methylcellulose 2%. In both groups a non-significant rise in IOP at day 1 was followed by a significant decline in IOP at day 3 to values below the pre-operative level (p < 0.05). At day 7 both groups had returned to pre-operative values. Post-operatively, spikes in intraocular pressure (> 25 mmHg) were seen equally in both groups. Patients with pre-operatively diagnosed open-angle glaucoma, high myopia and diabetic retinopathy are considered to be at high risk concerning post-operatively elevated IOP, but with small variation these patients followed the main trend.

Development of experimental chronic intraocular hypertension in the rabbit

There are many unanswered questions about chronic glaucoma which cannot be investigated in the available animal models. The present experiments were designed to develop a rabbit model of chronic intraocular hypertension with characteristics similar to human chronic glaucoma by ligating vortex veins or by making single or multiple intraocular injections of 0.5% or 1% alpha-chymotrypsin, 20% chondroitin sulphate, 2% hydroxypropyl methylcellulose, 2% sodium carboxymethylcellulose or 1% or 2% methylcellulose. Evaluation was based on the clinical findings, intraocular pressure and the retrograde axoplasmic transport function of the optic nerve using a horseradish peroxidase histochemical technique. Most methods either failed to produce moderate chronic intraocular hypertension or were associated with other complications. However, a reliable and relatively long period (eight weeks) of intraocular hypertension was developed by a series of four intra-anterior chamber injections of 1% or 2% methylcellulose. This model has been proved suitable for the study of structural and functional damage to the retina and optic nerve caused by chronic glaucoma.

Natural course of intraocular pressure after cataract extraction and the effect of intracameral carbachol

Intraocular pressure (IOP) is known to increase after intracapsular cataract extraction, extracapsular cataract extraction (ECCE), and ECCE with intraocular lens (IOL) implantation. Many pharmacological agents have been used to prevent this IOP rise. We conducted a two-phase, randomized, prospective study to evaluate the natural behavior of IOP after cataract surgery and the effect of intraoperative intracameral carbachol on it. In phase 1, 102 cases were randomly assigned to three groups for recording IOP at 24, 48, or 72 hours after ECCE. The IOP at 24 (mean 20.3 mm Hg) and 48 hours (mean 22.3 mm Hg) was significantly higher than the preoperative IOP (mean 16.1 mm Hg); 26.3% of cases in group 1A (24 hours) and 44.1% of cases in group 1B (48 hours) had IOPs greater than or equal to 25 mm Hg. In phase II, intracameral carbachol (0.01%) was used in 30 cases of ECCE and in 30 cases of ECCE with IOL implantation. The IOP at 24 hours (mean 16.3 mm Hg) was not significantly higher than the preoperative IOP and only 11.6% of the cases had IOPs greater than or equal to 25 mm Hg. The mean IOP at 24 hours without carbachol was significantly higher than the mean IOP at 24 hours with it. There was no statistically significant difference between IOP in the two groups one week after surgery.

Comparison of the postoperative intraocular pressure with Betagan, Betoptic, Timoptic, Iopidine, Diamox, Pilopine Gel, and Miostat

A randomized, masked study measuring postoperative intraocular pressure at 4, 8, and 24 hours, two to seven days, and one month after planned extracapsular cataract extraction with posterior chamber lens implantation was conducted. Seven commonly used ocular hypotensive agents and a control, given at the completion of surgery, were compared: timolol maleate (Timoptic), levobunolol hydrochloride (Betagan), betaxolol hydrochloride (Betoptic), pilocarpine hydrochloride (Pilopine Gel), carbachol (Miostat), apraclonidine hydrochloride (Iopidine), acetazolamide (Diamox). There were significant differences between agents. Miostat was the most effective in controlling postoperative IOP, followed by Timoptic. Diamox, Pilopine Gel, and Betagan were equally effective. Betoptic was somewhat less effective and Iopidine was not significantly better than the control.

Use of in vitro models of bovine corneal endothelial cells to determine the relative toxicity of viscoelastic agents

Healon, Viscoat and Amvisc Plus (Amvisc+) are commercial preparations containing hyaluronic acids of different molecular weights and viscosities. Cytotoxicity of these preparations to the corneal endothelium may be a factor in postsurgical recovery of the cornea. Using different in vitro models of bovine corneal endothelial cells (BCEC), three experiments to compare the possible detrimental effects of these viscoelastic agents were designed. In the confluent model, confluent BCEC were exposed to viscoelastic agents and the control to Balanced Salt Solution Plus (BSS+) for one hour and the nuclear density (nuclei/mm2) was assessed at 24 and 168 hours. At both times, the BCEC exposed to Healon showed the highest nuclear densities. In the preconfluent model, BCEC were treated for one hour at 48 hours post-seeding. The nuclear density of the BCEC was assessed at 24 hours. The BCEC exposed to Healon showed the highest density, followed by those exposed to Amvisc+ and then Viscoat. In the proliferation model, BCEC were cultured in media containing 1%, 5%, and 10% viscoelastic agents. The growth curves based on nuclear densities at 0, 24, 72, 120, and 168 hours in all treatment groups did not differ significantly from the control. The results indicate that the undiluted Healon was significantly less toxic in the preconfluent and confluent BCEC models.

Long-term results of extracapsular cataract extraction with posterior chamber lens implantation: sodium hyaluronate 1% vs hydroxypropyl methylcellulose 2%

We investigated the frequency of surgical complications and the long-term outcome in terms of visual acuity, intraocular pressure and post-operative complications in 206 extracapsular cataract extraction procedures with posterior chamber lens implantation using either sodium hyaluronate 1% (Healon) or hydroxypropyl-methylcellulose 2% over a follow-up period of 12 months. We found no significant difference in the results of using either of the two viscoelastic agents.

The glaucomas in aphakia and pseudophakia

Intraocular pressure may become temporarily or permanently elevated at various intervals following cataract surgery. There are several mechanisms by which glaucoma develops as a complication of the cataract extraction itself. The presence of a pseudophakos may or may not contribute to the pathogenesis. Important diagnostic clues include the anterior chamber depth, the presence or absence of an iridectomy, gonioscopic findings, and the appearance of the optic nerve head. Life-long medical treatment is frequently justified, as alternative laser or surgical modalities may not be successful. The exact causes for high failure of filtration surgery in aphakic eyes is not clearly understood; scarring of the conjunctiva, the vitreous, and altered characteristics of the aqueous humor have all been incriminated. Current research to improve surgical success includes the development of effective artificial drainage implants or the use of pharmacologic modulators of wound healing, which promote filtration by preventing scar formation.

Light and electron microscopic analysis of intraocular 2% hydroxypropylmethylcellulose

Twenty samples of 2% hydroxypropylmethylcellulose for intraocular surgery, obtained from two Brazilian laboratories, were studied to determine the presence and type of impurities in the solutions. These were compared with ten samples of balanced salt solution (control group). Using light and scanning electron microscopy, five types of particles were identified: cellulose fibers, vegetable flakes, crystals, glass fragments, and other impurities. At least one of these contaminants was present in each sample of 2% hydroxypropylmethylcellulose. The vegetable matter was also seen in a sample of the raw material from which the clinical material had been prepared. Control solutions (i.e., balanced salt solution) were free of vegetable matter and of crystals, but glass fragments and other impurities were present. The average number of foreign particles in the solutions of hydroxypropylmethylcellulose (91.2 and 96.7 particles per milliliter for each of the two groups) was statistically greater than in the balanced salt solutions (13.7 particles per milliliter).

Prospective comparison of the effects of Occucoat, Viscoat, and Healon on intraocular pressure and endothelial cell loss

We compared the effect of Occucoat (2% hydroxypropylmethyl-cellulose), Viscoat (sodium hyaluronate-chondroitin sulfate), and Healon (sodium hyaluronate) on postoperative intraocular pressure (IOP) and endothelial cell damage. One hundred fourteen patients having planned extracapsular cataract extraction with posterior chamber lens implantation using a viscomaterial were prospectively randomized into one of five groups. Group I received Occucoat which was removed from the anterior chamber at the conclusion of surgery. Group II received Occucoat which was not removed (retained). Group III received Viscoat which was removed, Group IV received Viscoat which was retained, and Group V received Healon which was removed. No prophylactic ocular hypotensive medications were given. Intraocular pressure was measured at four hours, 24 hours, one week, one month, three months, and one year postoperatively. Compared to preoperative IOP, all groups had a significant IOP increase at four hours. All but the Viscoat removed group (Group III) showed a statistically significant increase at 24 hours postoperatively (P less than .05). No group had a significant increase at one week or later. Specular microscopy showed no significant difference in cell loss between any of the groups at three months or within each group when compared to preoperative cell counts (P greater than .1).

Manipulative damage to the endothelium of infant and adult donor corneas

Six human donor corneas were studied with the scanning electron microscope to quantify the hazards to the endothelium during the excision of corneoscleral buttons. Although the number studied was small, it was found that: (1) striae were more numerous in the flaccid, very young, donor corneas (under 1 year old) than in the more rigid adult corneas: (2) iridocorneal endothelial touch can result in loss of the posterior membrane and death of the touched endothelial cells. This corroborates the findings of other investigators. Both findings are important, because these conditions reduce the quality of the donor cornea for transplantation.