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

The corneal endothelium

The endothelium is a monolayer of cells on the posterior corneal surface that transports water from the stroma into the anterior chamber. This movement of water counters a natural tendency for the stroma to swell and is necessary to maintain a transparent cornea. Embryologic studies, in particular the demonstration of the derivation of the endothelium from the neural crest, have provided insight into the factors that govern the response of this tissue to disease. In some species the endothelium can regenerate after injury, but in man cellular enlargement is the main mechanism of repair after cell loss. A clinical estimate of endothelial cell density and function is provided by specular microscopy, fluorophotometry and pachymetry. In this paper we review the development, structure and function of the corneal endothelium, and then consider the pathological processes that can affect this tissue.

Viscoelastic substances in ophthalmology

The desirable properties of a viscoelastic substance for ophthalmologic applications are intimately tied to its chemical and rheologic properties. This report describes the relevant rheologic properties (e.g., viscosity, viscoelasticity, pseudoplasticity, cohesiveness, and coatability) of the available viscoelastic substances and presents the general principles of their use as well as some specific technical aspects. In addition, the various uses of viscoelastic substances in ophthalmic surgery are outlined. There is no single ideal substance for all circumstances. With a knowledge of the rheologic properties of each substance, the ophthalmologist will be able to choose among the different ones as necessary to suit each clinical situation.

Hydroxypropyl methylcellulose in extracapsular cataract surgery with intraocular lens implantation: intraocular pressure and inflammatory response

We studied prospectively the effects of 2% hydroxypropylmethylcellulose (HPMC), instilled in to the anterior chamber during extracapsular cataract extraction with posterior chamber intraocular lens implantation in 122 patients. Significant pressure rise was noted at 12 and 24 hours post-operatively when HPMC was not removed at the end of surgery. This was prevented by washing HPMC from the anterior chamber at the end of surgery, or by using either acetazolamide or a combination of oxyphenbutazone and vitamin C without washing HPMC. There was no difference in intraocular inflammation between controls and the HPMC groups. The group receiving combined oxyphenbutazone and vitamin C had the least, the differences between these two groups being sufficient.

Postoperative intraocular pressure rises: a comparison of Healon, Amvisc, and Viscoat

A prospective randomized study was performed involving 200 patients divided into four groups: (1) Healon aspirated, (2) Amvisc aspirated, (3) Viscoat aspirated, and (4) Viscoat not aspirated. Postoperative intraocular pressures were measured at 4, 8, and 24 hours, two to three days, and one month. Significant differences between the groups were noted at four and eight hours; however, by 24 hours there were no significant differences. There were also no significant differences at two to three days and one month postoperatively. In this study, the Viscoat-not-aspirated group had the highest intraocular pressures followed, in decreasing order, by the Viscoat aspirated group, the Amvisc aspirated group, and the Healon aspirated group. From this study, I have concluded that Viscoat should be aspirated at the end of surgery to avoid postoperative intraocular pressure rises. Healon appears to be associated with lower intraocular pressures than the other two agents at four and eight hours postoperatively.

Experimental evaluation of a synthetic viscoelastic material on intraocular pressure and corneal endothelium

We compared the effects of 1.0% hyaluronic acid (Healon) and a synthetic viscoelastic polyacrylamide on postoperative intraocular pressure, the corneal endothelium, and various clinical parameters in rabbit and monkey models. Seven rabbit eyes received polyacrylamide and seven received hyaluronic acid during extracapsular cataract extraction with implantation of a polymethylmethacrylate posterior chamber intraocular lens. Intraocular pressure was measured preoperatively, immediately postoperatively, and at 1, 2, 4, 8, 12, and 24 hours postoperatively. Slitlamp examination was performed preoperatively and postoperatively at 3, 7, and 14 days. Axial corneal buttons were taken and scanning electron microscopy of the endothelium was performed. Sections of the globe were studied by light microscopy. Six monkey eyes received polyacrylamide, three received hyaluronic acid, and three received balanced salt solution to reform the anterior chamber after limbal incision with evacuation of aqueous. Intraocular pressure was measured preoperatively, postoperatively, and at 4, 8, 12, 24, and 48 hours postoperatively. Slitlamp examination was performed preoperatively, and at 1, 2, 7, and 14 days postoperatively. Specular endothelial microscopy was performed preoperatively and at 7, 14, and 90 days postoperatively. In the studies performed no significant difference between the eyes receiving polyacrylamide and hyaluronic acid was seen. In the rabbit and monkey models, polyacrylamide is as safe and biocompatible as hyaluronic acid.

An animal study of different treatments to prevent postoperative pelvic adhesions

A study was designed to test various high-molecular-weight solutions in the prevention of postoperative intraabdominal adhesions. The bicornuate rat uterus was used as the surgical model, and 80 mature white female rats underwent surgical injury of the right uterine horn. The rats were randomly divided into 5 groups: groups A, B, and C received 5 ml intraperitoneally of chondroitin sulfate, sodium carboxymethylcellulose, and 32% dextran 70, respectively; group D was treated with microsurgical repair; and group E, the control, received no therapy. The animals were killed postoperatively, and the adhesions were scored. Significantly better results in adhesion prevention were demonstrated in the sodium carboxymethylcellulose group vs. the other groups, except in group A where the difference was not significant.

Prophylactic treatment of intraocular pressure elevations after neodymium: YAG laser posterior capsulotomies and extracapsular cataract extractions with levobunolol

The prophylactic effect of topical 0.5% levobunolol on intraocular pressure (IOP) elevations after neodymium:YAG (Nd:YAG) laser posterior capsulotomies and extracapsular cataract extractions (ECCEs) was investigated in two separate, double-masked, placebo-controlled studies. In study 1, 42 patients received either levobunolol or vehicle 1 hour before a unilateral Nd:YAG laser posterior capsulotomy. Elevated IOP (greater than or equal to 10 mmHg) occurred in up to 38% of those in the vehicle group and none in the levobunolol group. Mean IOP increased up to 6 mmHg in the vehicle group, whereas it decreased up to 3 mmHg in the levobunolol group. In study 2, 41 patients received either levobunolol or vehicle immediately after a unilateral ECCE involving the use of a viscoelastic preparation and the implantation of a posterior chamber intraocular lens (PC IOL). The incidence of IOP elevations (greater than or equal to 10 mmHg) was up to 40% in the vehicle group and 19% in the levobunolol group. Mean IOP increased up to 9 mmHg in the vehicle group and up to 2 mmHg in the levobunolol group. Thus, marked elevations in IOP after posterior capsulotomies or ECCEs may be minimized by prophylactic treatment with levobunolol.

An experimental technique to study the turnover of concentrated hyaluronan in the anterior chamber of the rabbit

An experimental technique to study the turnover of hyaluronan in the anterior chamber in single animals has been developed. It is based on the fact that circulating hyaluronan labelled with tritium in the acetyl group is rapidly taken up by the liver and degraded to tritiated water. 3H-labelled hyaluronan was mixed with high concentration, high molecular weight hyaluronan (Healon) and injected into the anterior chamber of rabbits. The concentration of tritiated water in blood plasma was followed for up to 13 days. An initial rise of radioactivity in the blood was followed by an exponential decrease. From the exponential disappearance it was possible to calculate the rate of turnover of water in the body. This was used to correct the initial rise of tritium for water losses. After this correction the appearance of radioactive water in blood corresponded to the disappearance of hyaluronan from the eye plus a 45 min time-lag due to the catabolism in the liver. Using this technique it was found that trace amounts of radioactive hyaluronan and 0.055 ml and 0.2 ml of 1% hyaluronan exhibited half-lives in the anterior chamber of 1.5, 7 and 13 hr respectively. When the same technique was used for subcutaneously and intramuscularly injected hyaluronan half-lives of 50 and 30 hr, respectively, were recorded.

Efficacy and safety of hypromellose in ocular implant surgery

In order to assess the efficacy of hypromellose as a viscoelastic substance in cataract surgery with posterior chamber intraocular lens implantation, we studied a series of 88 cases who underwent surgery with either alternate use of a viscoelastic substance (hypromellose, 39 patients, or sodium hyaluronate, 5 patients) or air (44 patients) in the anterior chamber. Endothelial cell loss was least in the group in which air was used (18 +/- 3% cell loss, mean +/- SEM), compared with hypromellose (26 +/- 3%) and sodium hyaluronate (28 +/- 6%), but the difference in percentage cell loss between the groups did not reach statistical significance. Some operative difficulties were encountered in both groups. In both the air and hypromellose groups there were two patients with an early postoperative rise in intraocular pressure, but this was easily controlled, and in both groups there were two patients with postoperative corneal oedema which soon cleared. Visco-elastic substances used in this study were not shown to be superior to air in protecting the corneal endothelium. For this reason use of hypromellose should be confined to situations where its use is likely to confer some special advantage, as in the presence of a bound-down pupil in patient's with chronic glaucoma or perhaps to facilitate "in the bag" implantation.

Exogenous glycosaminoglycans stimulate hyaluronic acid synthesis by cultured human trabecular-meshwork cells

Addition of hyaluronic acid (50-200 micrograms ml-1) to the defined, serum-free media of cultured human trabecular-meshwork cells resulted in an increase of glycosaminoglycan (GAG) synthesis as measured by the incorporation of [14C]glucosamine. Lesser stimulatory effects were exerted by dermatan sulfate and chondroitin-4- or -6-sulfate. Nearly 90% of the labeled GAGs were found to be exerted into the medium and ea. 10% were associated with the cell layer. Mainly hyaluronic acid synthesis was stimulated by the exogenous GAGs. Analysis of the GAG-pattern revealed that exogenous hyaluronic acid stimulated hyaluronic acid synthesis (positive feedback), while exogenous dermatan sulfate and chondroitin sulfate had additional effects on chondroitin sulfate synthesis. Cell growth of these cultures, which exhibited a limited proliferative capacity (ca. 18 population doublings during their life span) was not affected by the GAG treatment. Thus, exogenous hyaluronic acid and to a lower degree dermatan sulfate or chondroitin sulfate appeared to interfere with the GAG-metabolism of these human trabecular-meshwork cells in culture.

Air, methylcellulose, sodium hyaluronate and the corneal endothelium. Endothelial protective agents

In a randomised trial the endothelial protective agent used during extracapsular cataract extraction and intraocular lens insertion was air in 19 eyes (group 1), methylcellulose in 25 eyes (group 2) and sodium hyaluronate in 22 (group 3). The cell population densities of each eye were estimated immediately before and three months after the operations to determine the degree of cell loss. Eyes showing mechanical (touch) damage on the second postoperative day were eliminated. The numbers of eyes in each group which showed a statistically significant cell loss were compared, and the mean cell losses in each group were tested for significant differences. It appears that air actually damages the endothelium while methylcellulose and Na-hyaluronate are not harmful, and afford a high, essentially equal degree of endothelial protection.

The use of hydroxypropyl methylcellulose in extracapsular cataract extraction with intraocular lens implantation

We conducted a prospective randomized clinical trial on the use of 2% hydroxypropyl methylcellulose and 1% sodium hyaluronate in the anterior chamber during anterior capsulotomy and nuclear expression in extracapsular cataract extraction with posterior chamber lens implantation in 70 patients. Both viscoelastic substances helped maintain the anterior chamber and facilitated the operation, although sodium hyaluronate was preferred. There was no excessive intraocular inflammation or toxicity noted with either agent. Patients given sodium hyaluronate had a larger increase in intraocular pressure during the early postoperative period (2.04 mm Hg) than did those given hydroxypropyl methylcellulose (1.1 mm Hg), but the difference was not significant. Nine weeks after surgery, the mean (+/- SD) central endothelial cell loss was 4.84% (+/- 7.26%) in the 17 eyes with sodium hyaluronate and 4.37% (+/- 9.84%) in the 53 eyes with hydroxypropyl methylcellulose. The intraocular pressure and corneal thickness were not significantly different before operation and nine weeks after it.

The use of PhEA 34c in trabeculectomy

PhEA 34c, a 1.9% solution of sodium hyaluronate (Healon = 1.0%) was injected intracamerally and between the scleral and conjunctival flaps after trabeculectomy in 15 eyes, while randomized controls received balanced salt solution (BSS). Anterior chamber depths in both groups in the early postoperative period were significantly different from baseline measurements, but were not different between the two groups at any interval. PhEA 34c did not prevent postoperative flat or shallow anterior chambers. There was no significant difference in the rate of success between the two groups for the duration of the study, but five patients in the PhEA 34c group developed loculated blebs.

Comparison of vitreous replacement with Healon and with HPMC in rabbits' eyes

Ten rabbits underwent vitreous aspiration and replacement by either Healon or Hydroxy Propyl Methyl Cellulose 2%. Four weeks' observation did not reveal noticeable differences between Healon and HPMC with regard to anterior chamber reaction, intra-ocular pressure or cataract. The vitreous reaction in eyes with HPMC was much more severe than in Healon eyes, with typical white precipitates and vitreous bands. Post-mortem examination confirmed the clinical findings.

Comparison of the effects of Viscoat and Healon on postoperative intraocular pressure

We compared the effects of Viscoat and Healon on postoperative increases in intraocular pressure in patients undergoing uncomplicated extracapsular cataract extraction with posterior chamber intraocular lens implantation in a prospective, randomized, single-masked study. Eleven eyes received Viscoat and 13 received Healon. The Viscoat or Healon was aspirated from the anterior chamber with the irrigation-aspiration tip of an automated irrigation-aspiration system at the end of the procedure. No prophylactic intraoperative or postoperative ocular hypotensive agents were used. Intraocular pressure was measured at three, six, 12, and 24 hours postoperatively. Compared with preoperative intraocular pressure, postoperative intraocular pressure was significantly increased in both the Viscoat group and the Healon group. Some postoperative intraocular pressures were as high as 50 to 60 mm Hg, despite removal of the viscoelastic substance at the end of surgery. There was no significant difference in the postoperative intraocular pressures of the Viscoat group and the Healon group.

Intraocular pressure after cataract surgery with Healon

We studied the intraocular pressure (IOP) following extracapsular cataract extraction and posterior chamber lens implantation in 75 cases. Sodium hyaluronate (Healon) was used in all cases. In 40 cases, Healon was left in the eyes; in 35, the eyes were irrigated to remove Healon from the anterior chamber. When Healon was left in the eyes, 35% had an IOP increase of greater than or equal to 20 mm Hg during the initial ten hours, compared to 11% of the group in which Healon was irrigated out. Twenty hours after surgery, the irrigated eyes had an average lower IOP than the nonirrigated eyes, 15.6 mm Hg versus 23.8 mm Hg.

Hyaluronate increases intraocular pressure when used in cataract extraction

A prospective randomised study of 26 eyes (24 patients) following uncomplicated intracapsular cataract surgery was carried out with three groups in which different agents were used to re-form the anterior chamber: air, seven eyes; sodium hyaluronate, seven eyes; and a combination of hyaluronate plus systemic acetazolamide, 12 eyes. The intraocular pressure (IOP) was measured by Goldmann applanation tonometry 16 hours before surgery and every eight hours after surgery for 72 hours. The IOP doubled in the two hyaluronate-treated groups for the first day following cataract surgery. By contrast, the IOP in the group receiving air initially decreased slightly. Throughout the study the effect of using acetazolamide was never statistically significant. After the first day and a half the differences in IOP among the three treatment groups disappeared, and the pressures returned to their preoperative values.

Intraocular lens implantation in acute angle closure glaucoma associated with cataract

We have performed planned extracapsular cataract extraction and implantation of a posterior chamber intraocular lens in four eyes of three patients undergoing surgery for acute angle closure glaucoma associated with cataract. Three of these four eyes suffered angle closure secondary to intumescent cataract. One suffered primary angle closure upon preoperative pupillary dilation prior to lens extraction. We have found no evidence of corneal decompensation, residual glaucoma, or increased surgical morbidity in our patients. We feel that acute glaucoma associated with cataract is not a contraindication to lens implantation.

Corneal endothelial loss with new intraocular lenses

When we compared the effect of a hydrogel intraocular lens on the corneal endothelium of rabbits to the damage produced by uncoated methylmethacrylate intraocular lenses and methylmethacrylate lenses coated with sodium hyaluronate or methylcellulose, we found that the endothelial damage produced by the hydrogel lenses in a standard 0.25 mm2 of contact was 3.6%. This value was not significantly different from that for the control corneas (0.4%). Uncoated methylmethacrylate lenses caused 62% endothelial loss but coating them with sodium hyaluronate or methylcellulose reduced the loss to 27% and 57% respectively. The results suggested that a hydrogel intraocular lens produces minimal endothelial damage and that coating a methylmethacrylate lens with sodium hyaluronate or methylcellulose does not provide reliable endothelial protection.

Exogenous Na-hyaluronate in the anterior chamber of the owl monkey and its effect on the intraocular pressure

Exogenous, ultrapure (sterile, pyrogen-free), non-inflammatory fraction of Na-hyaluronate (NIF-NaHA) was introduced into the anterior chamber of owl monkeys (Aotus trivirgatus), replacing approximately 48% or 77% of the aqueous humor and creating post-injection intraocular pressures (IOPs) below normal (5-10 mmHg) or above normal (40-60 mmHg), respectively. Five different molecular weight samples (MW 1.7, 3.4, 3.7, 4.5 and 4.9 X 10(6)) were used. All solutions contained 1% NIF-NaHA and, because of the varying molecular weights, the viscosities of the solutions ranged between 10 000 and 930 000 cSt. The IOP and the rate of export of the exogenous NIF-NaHA from the anterior chamber were measured. All solutions caused an increase in the IOP, and the maximum level occurred at 4 hr after injection. In all cases, the IOP returned to normal 24 hr after injection. The highest and most persistent increase in IOP was observed after the injection of the solution with the lowest viscosity (10 000 cSt). The smallest increases in IOP over the post-operative value were observed after replacement of the aqueous humor using those samples with viscosities of 10 0000 to 300 000 cSt. The turnover (export rate) of injected NIF-NaHA depends for the most part on the viscosity of the injected solution. With increasing viscosity the rate constant, and therefore the half-life, of the injected NIF-NaHA decreases. The volume fraction of the viscous solution replacing the aqueous humor is also a determining factor in establishing the turnover rate. The molecular weight of the injected NIF-NaHA did not change during that time (48 hr) in which a sufficient amount of sample for analysis could be obtained. No evidence was found for the presence of any kind of hyaluronic acid-degrading agent in the anterior chamber.

Complications of intraocular lenses. A historical and histopathological review

Recent improvements in intraocular lens (IOL) design, manufacturing techniques, and surgical techniques have greatly reduced the incidence of complications following implantation, and many authors now consider IOL implantation to be among the most safe and effective major surgical procedures. However, adverse reactions are still seen--some as late sequelae of earlier IOL designs and implantation techniques and some as sequelae of more recent implantations using "state-of-the-art" lenses and surgical techniques. Complications may be due to various factors, including surgical technique, IOL design, or the inability of some eyes with preexisting disease to tolerate an implant. The authors trace the evolution of IOLs since Ridley's first implant, summarizing the modifications in lenses and surgical techniques that were made as complications were recognized. They then review the clinical and histopathological features of selected cases from more than 200 IOLs and/or globes removed due to IOL-related complications and studied in the University of Utah Ocular Pathology Laboratory. It is hoped that this review will provide insights into the pathogenesis of IOL complications, enhancing the current success of implant procedures and stimulating further basic and clinical research in this area.

Biochemical studies on the use of sodium hyaluronate in the anterior eye segment. II. The molecular behavior of sodium hyaluronate injected into anterior chamber of rabbits

The behavior of sodium hyaluronate injected into the anterior chamber of rabbits was investigated using a 1% (w/v) solution of sodium hyaluronate having a molecular weight of 800K. Although the aqueous humor contained a considerable amount of reduced ascorbic acid, the molecular weight of sodium hyaluronate injected into the anterior chamber did not change. This was due to existence of a protecting factor for degradation of sodium hyaluronate in a low molecular weight fraction of the aqueous humor. The injected sodium hyaluronate was found to aggregate with proteins in the aqueous humor within 2 hrs. However, this aggregation did not affect the degradation of sodium hyaluronate with ascorbic acid. The hyaluronic acid content in the iris-ciliary body increased about three times as much as the normal level 2 hrs after the sodium hyaluronate injection. This result suggests that the injected sodium hyaluronate is not only eliminated through the angular aqueous plexus but also through the iris-ciliary body, followed by digestion with hyaluronidase in those tissues.

Biochemical studies on the use of sodium hyaluronate in the anterior eye segment. I. Variation of protein and ascorbic acid concentration in rabbit aqueous humor

To investigate the safety of the use of sodium hyaluronate in anterior segment surgery, the changes in protein, ascorbic acid and hyaluronate concentration in the aqueous humor, and intraocular pressure were followed after sodium hyaluronate was injected into the anterior chamber. When a 1% solution of sodium hyaluronate with a molecular weight of 800K was injected, the recovery patterns of protein and ascorbic acid concentration to normal levels were the same as the recovery patterns after injection of phosphate buffered saline which was the solvent for sodium hyaluronate. However, when a 1% solution of sodium hyaluronate with a molecular weight of 1640K or a 2% solution with a molecular weight of 800K was injected, it was observed that the recovery times of protein and ascorbic acid concentration to normal levels were longer than that required after injection of 1%, 800K sodium hyaluronate. Further, the recovery time of the aqueous humor components to normal levels was associated with the clearance time of sodium hyaluronate from the anterior chamber. The transient increase in intraocular pressure by injection of sodium hyaluronate was observed, but it disappeared in 12 hrs. The recovery time of intraocular pressure to normal level was independent of molecular weight and concentration of sodium hyaluronate tested.

Safety and efficacy of 2% methylcellulose in cat and monkey cataract-implant surgery

We evaluated the safety and efficacy of 2% methycellulose as an adjunct for cataract extraction with implantation in cat and monkey models. When used intraoperatively, methylcellulose reduced the iridovitreal bulge during surgery. No significant increase in clinical inflammation occurred nor was there statistically significant intraocular pressure elevation at 24 hours, 7 days, or 90 days. In the cat model, the central corneal thickness increased at day seven in both control and methylcellulose eyes; this thickness persisted to 90 days. The endothelial cell loss decreased significantly at day 90 in methylcellulose eyes. In the monkey model, no statistically significant increase in corneal thickness occurred in control or methylcellulose eyes at day seven. The endothelial cell loss was greater than in the cat model in both control and methylcellulose eyes; there was no statistically significant difference between the two. Two percent methylcellulose was safe in both the cat and monkey models. It facilitated surgery in both models and reduced the endothelial cell loss in the cat eye.