Ординатура / Офтальмология / Английские материалы / Small Incision Cataract Surgery (Manual Phaco)_Singh_2002

Fig. 3.29: Culture specimen taken using sterile swab stick from the operation table head rest

Fig. 3.30: Culture specimen taken using sterile swab stick being streaked on the MacConkey’s blood agar culture plate

media. It can be made very simply by the powder available from Himedia laboratories by dissolving 28 gm of powder in 1000 ml of distilled water and boiling for 15 minutes. This would also sterilize the medium and it is ready for use after cooling. The powder contains:

Alternately if the powder is not available the separate entities can be taken, mixed and steamed for 2 hours. The pH should be adjusted first to 6.8 then clear the fluid with egg albumin. Filter and bottle. Autoclave at 15 1bs pressure for 20 minutes or steaming for 30 minutes each day on three successive days.

Blood Agar

An enriched medium for general use in routine cultivation of the more delicate microorganisms like Neisseria meningitidis, N. gonorrhoeae and Diplococcus pneumoniae. The medium also serves as an indicator of hemolysin production by bacteria.

It is very simple to make. Add 6 to 10 percent defibrinated blood to melted nutrient agar and cool to 45 to 60°C. Pour plate or slant, incubate 24 hours to prove sterility.

STERILIZATION CONTROL

The infection control team which consists of a microbiologist must take regular samples from the different

areas sterilized or disinfected. Some of the quality checks necessary to be carried out are

Plate Test

One of the easiest to perform and tells us quite a bit about the cleaning tactics used for the particular room. This test would not be so effective in open areas but is quite reliable for closed areas like operating rooms.

For closed rooms Where operating rooms are concerned once we have assured ourselves there is no contaminated air coming in, with door closers, air curtains and filtered air-conditioned ducting, cleaning the room with detergents and disinfectants should clear the air of all bacteria. However this does not remain so through out the day, and it is noticed that after a few surgeries due to human beings inside the operating rooms bacteria do escape to contaminate the air. This can be effectively controlled by keeping a watch on the cleaning procedures and making sure a disinfectant mop is used after every procedure and on every item of the operating room.

However, testing for the efficacy of the cleaning procedures is devised by the PLATE TEST. Here a sterile bowl is used with sterile water and kept in the concerned room for 20 minutes. Should there be bacteria in the room they would settle down on the surface of the bowl of water. Thus skimming the surface a few drops are taken and placed on a Petri dish with culture media on it. This is incubated at 38°C for 48 hours and if this grows bacteria then we know our disinfectant procedures were not enough and we need to plough ourselves further. If it is negative then we can proceed with the same policy. This test should be ideally carried out every day, before every procedure in every room of the operating area.

For open areas Lounges where patients wait or the outside arenas are to be cleansed as well, if we would like to have a tight infection control in the operating area. After all these areas lead to the operating area—the most pious sanctum sanctorum of the hospital edifice.

The plate test is carried out every day every few hours, and an optimum time interval given to the hospital authorities where it can be stated that every four hours the hospital lounges should be cleaned with disinfectant to maintain a clean bacteria-free atmosphere. This can now be controlled by taking plate test samples every four hours before cleaning procedures are done and making sure the tests remain negative for growth in all the tests taken. If not the program needs to be revised and the hours shortened.

This test should also be carried out in the consultation areas and optimum time intervals for cleaning prescribed by the microbiologist on the infection control team.

Culture Test from Walls, Floor, Fixtures, Furniture

Everyday the different areas should be taken for culture, it is advised to take eight different areas for culture from every room everyday. Methodology for taking culture is to take a moist swab, by dipping a cotton tip applicator in sterile water and rubbing it in a streak fashion on the culture plate.

The culture plates are made in Petri dishes about 3 inches in diameter. The back surface of the Petri dish can be stroked with a marker pen and each culture plate divided into eight parts.

One culture plate can be ear marked for each room, and 8 objects from the room can be cultured. It is preferrable to always include the floor, of the room however different parts of the floor can be taken each day to ensure proper cleaning and disinfectant use. Other objects that can and should be cultured for are the fans, airconditioners, lights, walls, tables, chairs, stools and all the equipment present in that particular room. Like Boyles apparatus, phaco machines, etc.

All Fluids to be Cultured

All fluids used in the operating room must be sent for culture tests, sometimes this becomes less possible as the fluid is too little and necessary for parenteral application. However, every batch of fluids used can be sent for culture tests. This may not grow positive however its not growing positive itself is an indication of the efficacy of the program. This sets aside any debate that the fluid may have contained bacteria.

Of special importance is fluids used for intraocular use, or for intravenous use. As soon as each IV bottle is opened the first few drops from the IV set can be placed on a culture plate for incubation.

Many eye surgeons from our subcontinent have grown E. coli from the Ringer lactate used intraocularly. However, most often this has happened after a tragedy of multiple eyes have succumbed to postcataract surgery infection. Thus by performing this simple step we may be able to thwart further mishaps.

Should any one batch of fluids be found to be positive it is a good idea to report the matter so that others can be forewarned and to take every bottle from that batch.

All Fluids used Parenterally to be

Checked for pH Value

Great importance should be given to the pH of fluids inside the body especially where the eye is concerned. We presume that all fluids marked for parenteral or intraocular use come at the pH close to 7.4, however, it is alarming to note the amount of times I have personally seen surgery go wary only due to the fact that the pH was either 5.6 or above 8. This can produce havock on the patient’s cornea.

In 1992 over 300 cases were reported lost due to hazy opaque corneas following extracapsular cataract surgery in some states of India. This was followed by a widespread search for the culprit. What was found was alarming to all concerned, a balanced salt solution (BSS) was sold in small bottles. It was learned that this solution carried an alkaline pH, because while cleaning the glass bottles the last rinse of soap solution (BSS) was not totally washed out and the remaining soap solution left behind an alkaline pH which recked havoc on the cornea producing total blindness.

It took the investigating authorities over six months to procure this data and cause by which time multiple surgeries had been carried out with much devastation.

A simple technology to avoid such future catastrophies is to check out the pH on table before the surgery. A few drops of the fluid can be dropped on a simple litmus strip and one minute later the color change noted with a rough estimate of the pH value noted.

This should be ideally carried out for all cases.

Specialized Equipment Cultures

Special tests are performed for special machines, like the one available for the ethylene oxide sterilizer.

Biological chemical indicator One or more biological chemical indicator can be placed in the steam or ethylene

oxide test packs and the process passed through the sterilization cycles. If used to monitor a 270°F steam “flash” cycle, place a wire mesh bottom instrument tray and then proceed.

After sterilization processing has been completed, allow the biological chemical indicator to cool until safe to handle and open. Remove the indicators and allow to cool an additional 10 to 15 minutes. Observe chemical process exposure indicator on vial label to verify color change corresponding to sterilization cycle, i.e. ethylene oxide turns gas process indicator to gold and steam turns the steam process indicator to brown.

If chemical process indicator is unchanged, exposure to the sterilization process may not have occurred. Check the sterilization process.

If the chemical process exposure indicator on the vial label did change to the proper color and the indicator has cooled to touch, firmly seal the biological indicator by pushing the cap to close till the cap reaches second blue bar on the vial label.

Crush the inner ampoule from the outside wall of the plastic vial to ensure that the growth medium is released from the crushed ampoule and is in contact with the spore disk.

Place the activated indicators in an incubator and incubate it at 37°C for EO sterilization and 55°C for steam sterilization.

If there is a color change in the medium from deep blue to bright yellow and turbidity is evident, it means there is a positive growth. Indicators positive for growth will often be evident prior to maximum recommended incubation time, but indicators not evidencing growth mtiust be allowed to incubate for at least 24 hours (steam) and 48 hours (ethylene oxide) to assure confidence in the negative reading.

When, Where and Why to Use Biologicals

When?

•Once a day in every sterilizer

•Once a week in steam sterilizer cycle used

•Every steam load with implants

•Every EO load.

Three consecutive times before using new sterilizer and after repairs.

Where?

All sterilization processes.

Why?

•To challenge your sterilizer’s effectiveness

•To assure load sterilization parameters were up to standard.

Surgeons Hands Cultured

Right after scrubbing and ready for operation a surgeon’s hands should be regularly swabbed and taken for culture so that a close check can be carried out to the efficacy of the cleaning and scrubbing solutions.

There are many surgeons who believe in different technologies of scrubbing. While some would swear with the pounding away of epithelial tissue by a brush others would want to keep the epithelium intact at all times. While some would swear with a last dip into alcohol, others would keep alcohol well out of the way of surgeon’s hands.

However, it has been seen that three times to lather with soap and wash hands is a uniform tendency of most surgeons.

Linen and Textiles Cultured

Efficacy of sterilization on the different linens and textiles used in surgery should be tested by taking culture tests from these items just after surgery.

Viscoelastics 4

Viscoelastics 35

VP Gupta

Viscoelastic substances are currently essential for the successful performance of most of the intraocular anterior segment surgery, especially extracapsular cataract extraction and phacoemulsification with an intraocular lens implantation. Viscoelastics substances are considered as the most important addition in the armamentarium for microsurgery. Viscoelastic substances have revolutionised ophthalmic microsurgery particularly cataract surgery. Balazs coined the term viscosusrgery. Viscosurgery uses these agents to protect tissue surfaces, to create and maintain spaces, to facilitate intraocular tissue manipulations and to assist in haemostasis. During the evolution of IOL surgery it was observed that short contact between polymethyl methacrylate of IOL and the fragile endothelial cells of cornea could result in irreversible corneal damage leading to persistent corneal oedema. Binkhorst et al had recommended the air cushion technique to prevent the danger of contact between polymethyl methacrylate intraocular lens and the fragile endothelial cells of cornea. Fechner reported the use of methylcellulose successfully in intraocular lens implantations since 1976 to prevent the rubbing of PMMA of IOL against the endothelium of cornea. Sodium hyaluronate was used in the human eye as a vitreous substitute for the first time in 1972. First human studies of efficacy of hyaluronic acid were performed by Robert Stegmann and further confirmed and reported by Balazs et al in 1979. Ever since a variety

of viscoelastic substances have emerged.

PHYSICAL AND CHEMICAL PROPERTIES OF VISCOELASTICS

Viscoelastic substances possess viscous and elastic properties concomitantly. Viscoelastic substances are excellent for protection of tissue surfaces by forming even layers on the tissue or implant surfaces and act as ideal coating agents. Space maintenance by viscous materials is efficient resistance. However, the maintenance of space with viscoelastic substances does not depend on the outflow resistances, therefore, even effective in open

chambers. Surface application of viscoelastic materials maintains a stable irregular shape and is easily wiped off when touching an obstancle. The usefulness of a viscoelastic substance to protect tissue surfaces and for space maintenance depends mainly on their physical properties. The tolerance of viscoelastic substances within the eye depends on their chemical composition. An ideal viscoelastics substance should have the following properties:

1.It should be inert and iso-osmotic.

2.Viscoelastic should have a high viscosity for successful performance of various functions such as maintenance of anatomic spaces, tissue protection, intraocular tissue manipulations, lubrication and haemostasis.

3.It should be free of corpuscular elements and clumps.

4.It should be sterile, non-inflammatory, non-pyogenic, non-toxic and non-antigenic.

5.It should be reabsorbed without inflammation and should not interfere in the wound healing.

6.It should be optically clear. Viscoelastics should not impair the visibility inside anterior chamber.

7.Viscoelastics should possess pseudopasticity, i.e. the ability to pass through a fine cannula, i.e. a 30 gauze needle.

VISCOELASTIC SUBSTANCES

Currently used viscoelastics have been divided into two broad types (a) cohesive viscoelastics having high cohesive characteristics, e.g. healon (1% NaHa), Healon GV (1.4 Va Ha) (b) dispersive viscoelastics—These are noncohesive viscoelastic. These materials adhere to ocular surfaces. Dispersive viscoelastics provide a protective coating for corneal endothelium without excessive coakage from AC.

The following viscoelastic substances are described in literature:

1.Hyaluronic acid

2.Methylcellulose-Hydroxypropyl methylcellulose

3.Chondroitin sulphate

4.Polyacrylamide

5.Collagen—human placental collagen type IV

6.Poly TEGMA—Triethylene glycol monomethacrylate

Hyaluronic Acid (Sodium Hyaluronate)

It is a naturally occurring mucopolysaccharide. It consists of a long unbranched chain of alternative N-acetyl-gluco- samine and sodium gluconate. Hyaluronic acid is present in abundance in vitreous humor and trabecular meshwork. Corneal endothelium is naturally covered with a layer of sodium hyaluronate. It is an inert, totally transparent, non osmotic viscoelastic material composed of 98 per cent water and is highly viscous, 400,000 times more viscous than saline. It is a viscoelastic with pseudophastic properties. It is not metazolised or degraded.

Healon—(It contains sodium hyaluronate 1%) it is derived from a natural source-rooster comb. It was the first viscoelastic used in anterior segment surgery. Physical properties are molecular weight 1-2 million daltons, viscosity 700000 centipoise, osmolarity 340 mOSM/kg. storage 2-8°C, pH 7.2, shelf life two years. It is available in sterile, sealed 0.5 to 10 ml glass syringes. Blue tint may be given to facilitate intraocular visualisation. It is the viscoelastic most frequently used in cataract surgery because of its characteristics and qualities during the procedure.

Disadvantages—It is very expensive, not available universally and difficult to dilute hence relatively large amount of the material may be left in the anterior chamber and cause dangerous rise of intraocular pressure postoperatively.

•Healon GV—It is sodium hyaluronate 1.4 per cent. The viscosity of healon GV is 10 times higher than that of healon because of higher concentraction and molecular weight.

•Amvisc—It contains sodium hyaluronate 1-1.4 per cent. It is 20 times more viscous than chondroitin sulfate

•Amvisc plus—It is 1.6 per cent sodium hyaluronate. Its molecular weight and viscosity is less than healon. It is 30 per cent more viscous than amvisc.

•Three per cent sodium hyaluronate (Amo vitrex)— is the highest concentration available. Its molecular weight is 0.5 million daltons and viscosity— 30,000 cct, It has low cohesive properties.

Methylcellulose

Methylcellulose is a viscous, transparent, non-irritating, water soluble compound. It is nearly inert chemically. It

is stable and can be sterilised by boiling. It does not support the growth of micro-organisms.

Methylcellulose used for intraocular surgery is a highly purified brand of medical use grade hydroxypropyl methylcellulose (HPMC). It is a synthetic modification of methylcellulose. HPMC 2 per cent is freely available commercially. The hydroxypropyl and methyl groups replacing hydrogen groups increase its hydrophilicity. The basic molecule is D- glucose. Two monomers of glucose combine to form cellobiose, which differs from dextrose only in the way the 2 monomers are stereochemically connected: in cellobiose the bonding is beta-glycosidic, in dex–trose alpha glocosodic. The human enzymes are incapable of breaking cellobiose bonding. HPMC is a dispersive viscoelastic agent. Its MW is 90000 Daltons. HPMC is less viscous than healon due to low viscosity at zero shear rate 40000 PS (800020000). The dispersive nature causes better adherence of viscoelastic agent to the corneal endothelium resulting in better protection of corneal endothelium against fluid turbulence and lens fragments during phacoemulsification. It lacks pseudoplastic characteristic and does not pass easily through 30 gauge cannula. It predominantly protects tissues surfaces against touch by implant, instruments, etc. It is a non-physiological and non-metabolic substance consisting of large polymers.

Preparation

Preparation of 2 per cent hydroxypropyl methylcellulose for intraocular use.

The medical use grade hydroxypropyl methylcellulose of highest purity which is commercially available as methocel E-4 M premium of Dow chemical corporation is recommended. Dissolve 10 g of methocel E-4 M premium in 150 ml of boiling balanced salt solution (BSS). Add 350 ml of icy BSS solvent. This 2 per cent HPMC solution is stored in a refrigerator overnight at 0 to 10°C in lightly closed glass bottles. The preservatives like benzalkonium, chlorbutanol, thiomersal are not used because of their endothelial toxic effects. However, addition of 5 mg of patent blue V (sulphan blue) has been recommended. Next day the solution is warmed to 40°C to reduce its viscosity. The solution is now filtered through a filter tube (pore size of 0.5 to 0.8 um). This filtration procedure is necessary to remove crystalline complexes which form corpuscular elements. The filtered solution is poured into 3 ml glass vials and sealed with a rubber

stopper and aluminium cap and then sterilised by autoclaving at 120°C for 30-40 minutes. The solution is also available in special pre-filled syringes. The main disadvantage of pre-filled syringe is that usually great force is applied to push later half of the solution in the anterior chamber.

Advantages of HPMC

It is well-tolerated by corneal endothelium. It is cheap and universally available. It can be easily prepared for intraocular use. It can be autoclaved and resterilised. Because of its highly hydrophilic and easily dilutable property most of it can be easily irrigated from the eye. The fate of the residual HPMC in the anterior chamber after irrigation is not known. Fleming et al have shown that methylcellulose inside the eye is harmless. According to Fechner, if 20 per cent of what was injected into AC, i.e. 0.5 ml of residual HPMC is left in AC, this is equivalent to 2 mg of dry substance of methylcellulose, which is a inert substances and did not cause any local or systemic complication.

Contaminants/Particulate matter in HPMC

Rosen et al had raised serious concern about safety of intraocular ocular use of hydroxypropyl methylcellulose because of high density of particulate matter in the solution. However, Mamose et al examined the number of insoluble paprticles of verious sizes in one ml of 5 viscosurgical solutions and concluded that methylcellulose solution had 10 times less particles of various sizes (1-30 mm or more in diameter) as compared to Viscoat, Amvisc and Healon.

Systemic safety The process by which methylcellulose is cleared from human body is till not known. However, the doses used intraocularly are very small and most of the solution is irrigated at the end of surgery. The residual HPMC is clinically insignificant and unlikely to cause any toxicity. Methylcellulose has long been used in the preparation of injectable preparation of prednisolone acetate and hydrocortisone acetate. Oral consumption of large doses in soft ice creams is not known to cause any toxicity.

Endothelial cell loss It is well-established that endothelial cell loss with use of HPMC during IOL implantation is lower in comparison to air. There is no statistically significant difference in the endothelial cell loss during IOL implantation with Healon (20.7 +15.6) and 2 per cent HPMC (18.1 +14.9%).

Disruption of blood aqueous barrier Fluorophotometric studies have shown that the disruption of blood aqueous barrier with 2 per cent HPMC in intraocular surgery is similar to that caused by sodium chondroitin sulphate or sodium hyaluronate.

Postoperative glaucoma Postoperative glaucoma is not a common complication with 2 per cent HPMC. This has been attributed to the hydrophilic nature and easy dilutability of HPMC. However, the potential drawback is the difficulty of completely removing HPMC due to its dispersive nature, possibly resulting in an increased postoperative IOP.

Chondroitin Sulphate

It is the naturally occurring glycosaminoglycan. It is a sulphated and negatively charged viscoelastic substance. It forms a better coating of positively charged IOL. It reduces electrostatic interaction between IOL and endothelial cells.

Disadvantages

1.It is not a pseudoplastic substance—extremely high pressure is exerted for injection through a 30 G cannula

2.Maintenance of anatomic spaces (AC depth) is poor due to low viscosity of chondroitin sulphate 20 per cent.

3.50 per cent chondroitin sulphate solution damages corneal endothelium due to hyperosmolarity

4.Its yellow colour affects transparency and visibility through AC

•Viscoat—It contains 3 per cent sodium hyaluronate plus 4 per cent chondroitin sulphate. Its molecular weight is 600000 daltons and viscosity at zero sheer rate is 40000 CPS, as it is a dispersive viscoelastic agent, it is a superior coating substance and is superior to healon in preventing corneal endothelial cell loss during phacoemulsificationGlasser 1989

•Orcolon—It is the 4.5 per cent polyacrylamide solution. It is a synthetic polymer. It is hydrophilic, non-toxic and non-inflammatory. It has been recalled from the market due to occurrence of several cases of severe uveitis and glaucoma days to weeks following surgery.

•Poly TEGMA—It is a highly hydrophilic polymer poly (triethylene glycol monoacrylate) a cross linked gel. The new polymer poly TEGMA was characterised by high biological tolerance after its

implantation into the anterior chamber of rabbits. Poly TEGMA 40 per cent might be considered as a potential viscoelastic material in humans.

Uses of Viscoelastic Substances

Viscoelastic substances are used in cataract surgery, cornea grafting, glaucoma filteration procedures, vitreoretinal surgery, strabismus surgery, lacrimal surgery, evacuation of hyphaema and management of dry eye.

1.Viscoelastics in cataract surgery—Use of viscoelastics have revolutionised the cataract surgery. Viscoelastics have become indispensable in all forms of cataract surgery. Viscoelastic substances are routinely used intraoperatively in ECCE, phacoemulsification, nonphaco small incision cataract surgery and paediatric cataract surgery with intraocular lens implantation. Viscoelastics are also essential in secondary and scleral fixated IOL surgery and IOL exchange or explantation surgery. Viscosurgery uses viscoelastics to protect tissue surfaces, to create and maintain anatomical spaces to facilitate tissue manipulation in anterior chamber and to assist in haemostasis. Various uses of viscoelastics in cataract surgery are as follows:

a.Maintenance of deep anterior chamber during surgical manipulation. Comparative studies have demonstrated that 2 per cent HPMC, Healon, Amvisc, and Viscoat are all effective in the maintenance of deep anterior chamber during various stages of cataract surgery, e.g. during capsulotomy, capsulorhexis, before nuclear expression, cortical aspiration, insertion and manipulation of IOL, cutting large anterior capsular flap, etc.

b.To combat vitreous upthrust—all viscoelastics are effective in controlling positive vitreous pressure. High viscosity viscoelastics are superior in combating vitreous upthrust.

c.Facilitates in the bag insertion of IOL by inflating the capsular bag prior to IOL insertion.

d.Viscoelastics protect the corneal endothelium from mechanical trauma during various stages of cataract surgery—viscoelastic substances are injected into the AC from the beginning of cataract surgery to facilitate anterior capsulotomy, capsulorhexis, manipulation of various instruments inside AC and expression of nucleus. Maintenance of deep AC with viscoelastics inflate the capsular bag which results in easier cortical aspiration and also prevent damage to corneal endothelium and posterior capsule. It also helps in removing anterior

capsule after IOL insertion following envelope technique. Viscoelastics filled in AC and a drop of it on the IOL optic provides complete corneal endothelial protection during IOL implantation and dialing of IOL. Glasser et al in a recent study reported superior ability of viscoat to prevent corneal endothelial cell loss during phacoemulsification with IOL implantation when compared to Healon. This superiority has been attributed to the presence of chondroitin sulphate in viscoat. Chondroitin sulphate remains adherent to the corneal endothelium.

e.Injection of viscoelastics into AC is of great help during different steps of phacoemulsification and non-phaco small incision surgery. Injection of viscoelastic into the cleavage plane between the lens nucleus and cortex termed as viscodissection greatly facilitates phacoemulsification of nucleus. The technique of nucleus removal by injecting viscoelastic in AC after capsulorhexis during ECCE is being practised successfully by many surgeons.

f.Protection of anterior hyaloid face during posterior capsulotomy and primary posterior capsulorrhexis.

g.Facilitates removal of residual cortex in the presence of posterior capsule rupture. Aspiration of lens matter is done without any irrigation in such cases (dry aspiration)

h.Injection of sodium hyaluronate beneath the subluxated lens simplifies lensectomy by elevating the lens and prevention of total luxation.

i.Viscoelastics have also been used successfully to prevent drying of corneal epithelium during anterior segment surgery including penetrating keratoplasty.

j.Management of Descemet’s detachment— Descemet’s detachment from corneal stroma is a common complication during cataract surgery. Sodium hyaluronate injection has been used successfully in the repair of stripped Descemet’s membrane. The tamponading effect of viscoelastic keeps the detached Descemet’s membrane in the normal anatomic position.

k.Viscoelastics in glaucoma filteration surgeries—The advantages of viscoelastics during glaucoma filteration procedures include—to prevent shallow anterior chamber during intraoperative and postoperative period, prevention of hyphaema, facilitates bleb formation and maintenance of permanent blebs and lower long-term postoperative IOP.

Healon (Sodium hyaluronate) has been the most often studied viscoelastic with regard to behaviour of viscoelastics in glaucoma filtering surgery. It is effective in post-trabeculectomy anterior chamber reformation. Juzych et al reported usefulness of healon in the management of postoperative ciliary block. There have been reports of intraoperative use of viscoelastics to prevent various post-trabeculectomy complications such as flat anterior chamber, detachment, hypotony, etc. Eugene et al has recently reported the results of a survey of members of the American Glaucoma Society about the use of viscoelastic materials in the post-trabeculectomy patient in the office at the slit lamp for anterior chamber reformation 75 per cent of the respondents practised injection of viscoelastics postoperatively at the slit lamp in the office. Healon (60%), viscoat (17%) and Healon GV (7%) were the three most often used viscoelastics. Injection of viscoelastics in the anterior chamber is not without complications. It may cause corneal, iris or lens damage and elevation of intraocular pressure. However, Gerber et al did not report any of these complications in a series of 19 anterior chamber reformations. Injection of viscoelastic in an hypotonous eye with patent sclerostomy is unlikely to cause elevated IOP. Incidence of endophthalmitis was 1 per cent in this survey.

l.Use of viscoelastics has been recommended for control of intraocular bleeding, e.g. hyphaema and suprachoroidaehaemorrhage. A technique of safe evacuation of traumatic hyphaema using viscoelastic properties of healon has been described. Healon maintain a deep AC, stable IOP, protects lens, corneal endothelium and allows clear observation.

m.Viscoelastics in vitreo-retinal surgery—Sodium hyaluronate has been used as vitreous substitute. Suprachoroidal implantation of sodium hyaluronate can be used as internal buckling procedure in the retinal detachment surgery. Sodium hyaluronate has also been used in cases of retinal detachment with giant retinal tears. unrolling of giant retinal tears and approximation with underlying retinal pigment epithelium has been performed with use of sodium hyaluronate. The procoagulant effect of intraocular sodium hyaluronate after phakic diabetic vitrectomy has been reported by Pocker et al. Sodium hyaluronate has

also been advocated for viscodelamination of the vitreoretinal juncture in severe diabetic eye disease.

n.viscoelastics in lacrimal surgery—Sodium hyaluronate has been successfully used in lacrimal sac identification during dacryocysto-rhinostomy. Injection of sodium hyaluronate in the lacrimal sac helps in locating cut medial canaliculi and also facilitates passage of lacrimal probes for repair of lacerated canaliculi.

o.Sodium hyaluronate has been successfully used in adjustable strabismus surgery as a biologic sleeve. It reduces postoperative muscle adhesions and increases the period of suture adjustability.

p.Sodiumhyaluronateandchondroitinsulphatehave been used in the management of dry eye and some

ocular surface disordes. Sand BB reported marked subjective and objective improvement in the patients of keratoconjunctivitis sicca

Complications

Postoperative complications following intraoperative use of viscoelastic substances are as follows:

1.Elevated intraocular pressure (IOP)

2.Corneal endothelial toxicity

3.Inflammation

4.Dilated fixed pupil

Elevated IOP postoperatively following use of viscoelastic substances remains the most common ocular toxic effect of viscoelastic agents, It occurs with all viscoelastic substances. It occurs 2-24 hours after surgery with a peak at 6-8 hours. It resolves spontaneously within 72 hours. The IOP may be elevated to dangerous levels threatening the functioning of optic nerve and corneal endothelium. Rise in IOP is more if viscoelastic material is not aspirated from the anterior chamber at the end of surgery. However, one must remember that IOP may be elevated despite aspiration of viscoelastic substance from the anterior chamber. The mechanism of postoperative IOP increase is not yet fully understood. It is assumed that the mechanical obstruction of trabecular meshwork by viscoelastic substances decreased the outflow pathway resulting in glaucoma. Individual variation in postoperative IOP elevation may be explained on the basis of variation in trabecular pore size, polymer size of hyaluronic acid, amount of fibrin, albumin, residual viscoelastic material in AC, viscosity and molecular weight of viscoelastic substances and inflammatory products produced after surgery. Elevation in IOP may occur even with administration of antiglaucoma treatment like acetazolamide. Elevation of IOP also occurs following ICCE with viscoelastic substances.

The clearance of the viscoelastic agent through the trabecular meshwork is believed to be dependent upon the viscosity and molecular weight. The lower the viscosity and molecular weight of viscoelastic material, the faster is its clearance through the trabecular meshwork. HPMC is less viscous and has a lower molecular weight than viscoat causes less IOP increase.

Prevention—Aspiration/removal of viscoelastic at the end of surgery. Removal of viscoelastic material may be done either by completely aspirating or by diluting the viscoelastic substance. Aspiration of viscoelastic agent in bulk ensures complete removal but results in loss of anterior chamber causing more endothelial damage. Removal by dilution of viscoelastic agent ensures maintenance of anterior chamber depth and slow removal by irrigation and aspiration. The viscoelastic agent should be aspirated thoroughly from the retrolental space, the capsule fornix and the anterior chamber using an irrigation aspiration tip. First the optic edge is titled with a spatula and the I/A tip inserted behind the optic. After aspiration of the central portion of viscoelastic material the I/A tip is swept across and along the capsule equator to capture peripheral residual viscoelastic material. The viscoelastic agent from the AC is aspirated circumferentially from the retroiridal and preiridal spaces. The I/A tip should always be kept away from the endothelium and the angle of AC. Despite thorough removal of IOP both HPMC and viscoat cause a significant IOP increase.

•Postoperative monitoring of IOP is necessary after ECCE small incision cataract surgery and administration of antiglaucoma drugs in patients with high IOP is recommended.

•Prophylactic use of antiglaucoma drugs. We routinely administer tab acetazolamide 250 mg following ECCE with PC IOL for two days. Timolol maleate 0.5 per cent bid is added in appropriate cases after monitoring IOP on first postoperative day we routinely give intravenous mannitol 1 g/kg body weight 6-8 hours following ECCE with PC IOL surgery provided there is no contraindication. However, despite IV mannitol and oral acetazolamide and aspiration of HPMC, we still encounter dangerous elevations of IOP in some

cases.

Inflammatory potential and endothelial cell toxicity has been variably reported. Intraocular inflammation and subsequent bullous keratopathy have been reported following the reuse of injection cannulas of healon. It has been attributed to denatured healon by disinfectants or autoclaving. Chondroitin sulphate being an hyperosmotic

agent can cause damage to corneal endothelium due to dehydration because of its high osmolality. Initial formulations of chondroitin sulphate caused several cases of acute band keratopathy due to its high phosphate concentration, According to recent reports toxic endothelial cell destruction syndrome occurs due to intracameral injection of toxic detergent residue due to contamination inside reusable cannula 0.2 per cent chlorhexidine digluconate has also been reported to be endothelial toxic. The use of reusable cannula must be avoided. Disposable cannulas should be used where-ever possible.

Author is using HPMC 2 per cent in ECCE with posterior chamber IOL for senile and paediatric cases for last 15 years. Author has encountered severe unexpected diffuse corneal oedema on the first postoperative day after ECCE with posterior chamber IOL with intraoperative use of 2 per cent HPMC in 1 per cent of cases. In some patients the corneal oedema is maximum on 2nd postoperative day. This corneal oedema is usually associated with ocular hypertension and dilated pupil or decreased reactivity of pupil. This postoperative elevated IOP developed despite routine prophylactic administration of acetazolamide 250 mg 6 hourly in all ECCE with PC IOL implantation. Routine dilatation of pupil with cycloplegics in early postoperative period in such cases results in dilated fixed pupil which resists constriction with topical pilocarpine therapy. Persistent corneal oedema and elevated IOP have been noted in these patients. Although mechanical trauma is usually considered to be the most significant factor in the corneal endothelial damage during ECCE with IOL surgery resulting in postoperative corneal oedema. However, corneal decompensation out of proportion to the degree of surgical trauma may be traced to the unrecognised preoperative endothelial dysfunction or to toxicity of intraocular medications used during surgery.

The medications used inside AC during ECCE are 2 per cent HPMC, 0.3 ml of preservative free epinephrine in 500 ml of BSS and diluted pilocarpine to constrict pupil after insertion of PC IOL.

In authors opinion, viscoelastics may be implicated in the aetiology of unexplained corneal oedema as it was associated with elevated IOP in all such cases. Tan and Humphry have reported that a total of 1.67 per cent of eyes operated on using hypromellose developed a nonreactive semidilated pupil whereas none of the eyes from the control group developed this phenomenon. They concluded that there is a probable link between the intraocular use of hypromellose and abnormal pupil after

cataract surgery. Eason and Seward suggested that sodium hyaluronate and two per cent HPMC have similar effects on the pupil after their use in cataract surgery. Two per cent of pupils were partially reactive in both healon and HPMC groups

Comparative Studies Using Different Viscoelastics

Liesegang et al compared the efficacy and complications of 2 per cent HPMC and 1 per cent sodium hyaluronate in ECCE with PC IOL implantation in 70 patients. although both VE agents maintained anterior chamber and facilitated the surgery, sodium hyaluronate was preferred. There was no excessive intraocular inflammation with either agent. Sodium hyaluronate caused greater rise in IOP than HPMC but the difference was not significant. Mean endothelial cell loss and corneal thickness were also not significantly different. Intraocular pressure doubled for the first postoperative day following uncomplicated ICCE with AC reformed using sodium hyaluronate with or without systemic acetazolamide. Healon and viscoat both caused significant and comparable elevation of intraocular pressure. Some postoperative IOPs may be as high as 50 to 60 mm hg despite removal of VE agent at the end of surgery. (Baren). Fry observed that postoperative IOP rise was lower with healon as compared to Amvisc and Viscoat. Viscoat (not aspirated) group caused highest IOP rise. Retained Viscoat group patients had more incidence of patients with IOP greater than 30 mm hg. However, retained Viscoat may have better protective effect on endothelium. In one study although the effects of ocucoat (2% HPMC), Viscoat, Healon and Healon GV on postoperative IOP and endothelial cell loss after phacoemulsification were comparable among four groups. The high molecular weight viscoelastics (Healon and Healon GV) performed better as viscosurgical tool during phacoemulsification.

Viscoat tended to trap nuclear fragments and air bubbles which decreases visibility during surgery. Space maintenance and injection case were significantly better with Healon and Healon GV due to their high molecular weight Huts. Kohnen et al evaluated IOP rise with healon and healon GV in sutureless cataract surgery with foldable IOL implantation. There was no statistically significant difference in the highest mean IOP elevations between both the viscoelastics but standard deviations were higher in the Healon GV group at 6 and 24 hours groups. Both viscoelastics can be equally removed from AC. Incidence of high IOP using high viscosity hyaluronic acid viscoelastics can be minimised by meticulous removal of

viscoelastics. Rainer et al compared IOP rise after bilateral small incision cataract surgery using two dispersive viscoelastic agents ocucoat (HPMC 2%) and viscoat sodium chondroitin sulphate four per cent—(sodium hyaluronate 3%) Viscoat caused a significantly higher IOP rise and significantly more IOP spikes than ocucoat in the early postoperative period.

FURTHER READING

1.Barron BA, Busin M, Page C et al: Comparison of the effects of Viscoat and Healon on postoperative intraocular pressure. Am J Ophthalmol 100: 377-84 (Medline), 1985.

2.Brown GC, Benson WE: Use of sodium hyaluronate for repair of giant retinal tears. Arch Ophthalmol 107: 1246, 1989.

3.Clorfeine GS, Parker WT: Use of Healon in eye muscle surgery with adjustable sutures. Ann Ophthalmol 19: 215, 1987.

4.Eason J, Seward HC: Pupil size and reactivity following hydroxypropyl methylcelluose and sodium hyaluronate. Br J Ophthalmol 79: 541-43, 1995.

5.Fechner FU and Fechner MU: Methylcellulose and lens implanatation. Br J Ophthalmol 67: 259-63, 1983.

6.Fry LL: Postoperative intraocular pressure rises: A comparison of Healon, Amvisc, and Viscoat. J Cataract Refract Surg 15: 415-20 (Medline), 1989.

7.Gerber SL cantor LB: Slit lamp reformation of the anterior chamber following trabeculectomy. Ophthalmic Surg 23: 784-88, 1992.

8.Glasser DB, Osborn DC, Nodeen JF et al: Endothelial protection and viscoelastic retention during phacoemulsification and intraocular lens implantation. Arch Ophthalmol 190: 1438-40, 1991.

9.Glasser DB, Schultz RC, Hyndiuk RA: The role of viscoelastics, cannular and irrigating solutions additives in post-cataract surgery corneal edema: A brief reviews. Lens Eye Toxic Res 9: 3-4, 1992.

10.Hurwitz JJ, Nik N: Lactimal sac identification for dacryocystorhinostomy. The role of sodium hyaluronate. Can J Ophthalmol 19: 112, 1984.

11.Hutz WW, Eckhardt HB, Kothnen T: Comparison of viscoelastic substances used in phacoemulsification. J Cataract Refract Surg 22: 955-59 (Medline), 1996.

12.Kohnen T, Von Ehr M, Schutte E et al: Evaluation of intraocular pressure with Healon and Healon GV in sutureless cataract surgery with foldable lens implantation. J Cataract Refract Surg 22: 227-37, 1996.

13.Lavin MJ, Leaner PK: Sodium hyaluronate and giant retinal tears. Arch Ophthalmol 108: 480, 1990.

14.Lerner HA, Boynton JR: Sodium hyaluronate as an adjunct in lacrimal surgery. AM J Ophthalmol 99: 365, 1985.

15.Liesegang TJ, Bourne WM, Istrup DM: The use of hydroxypropyl methylcellulose in extracapsular cataract extraction with intraocular lens implantation. Am J Ophthalmol 102: 723-26 (Medline), 1986.