Commonly used intraocular medications and the corneal endothelium

Presumed herpetic endotheliitis following phacoemulsification surgery*

The authors present an observational case series. Three cases of presumed herpetic endotheliitis presented as cases of pseudophakic bullous keratopathy many years after successful phacoemulsification surgery. All patients had reduction of vision in the involved eye, corneal oedema and secondary glaucoma. The patients were treated with medical therapy consisting of topical corticosteroids, antiviral and antiglaucoma drugs. Resolution of corneal oedema, control of glaucoma and restoration of visual acuity were achieved in all cases. Specular microscopy performed thereafter demonstrated relatively normal endothelial cell counts. The authors conclude that pseudophakic bullous keratopathy occurring after phacoemulsification surgery may be caused by herpetic endotheliitis.

Toxic endothelial cell destruction from intraocular benzalkonium chloride

PURPOSE

To present a cluster of cases of corneal edema occurring after phacoemulsification.

SETTING

Regional hospital in rural Australia.

METHODS

This retrospective case series comprised 12 patients from a single surgical list comprising 19 cases who developed persistent corneal edema after having phacoemulsification.

RESULTS

After 6 months, the edema improved in 1 patient. Inadvertent intraocular use of balanced salt solution (BSS) preserved with benzalkonium chloride was found to be the cause of this serious complication.

CONCLUSIONS

Benzalkonium chloride in concentrations commonly used extraocularly is highly toxic to the corneal endothelium. Every possible safeguard should be taken to prevent inadvertent intraocular use of such preserved solutions.

Maintenance of mydriasis with one bolus of epinephrine injection during phacoemulsification

Surgically-induced miosis commonly occurs during cataract extraction surgery, complicating removal of lens cortex and placement of a posterior chamber intraocular lens. To maintain intraoperative mydriasis, one bolus of epinephrine injection was used in our study. The pupillary response to various doses of intracameral epinephrine (0.1 ml of 1:25,000, 1:50,000, 1:100,000, 1:200,000, 1:400,000) was assessed in 60 consecutive patients. The pupil size was measured just prior to the incision, one min after epinephrine injection, after phacoemulsification and after irrigation/aspiration. There was no significant difference among the mean mydriatic responses to the epinephrine concentrations we tested. The 1:400,000 concentration appeared to be as effective as 1:25,000, but two cases of the 1:400,000 group failed to maintain the pupil diameter after irrigation/aspiration. In addition, we found that blood pressure did not elevate after injection of any concentration of epinephrine. We concluded that one bolus of an extremely dilute concentration of epinephrine (i.e., 1:400,000) injection might be effective in maintaining mydriasis during cataract surgery without systemic side effects.

Intraocular adrenaline maintains mydriasis during cataract surgery

Cataract surgery is performed more easily if mydriasis can be maintained until the intraocular lens has been inserted. Intraocular irrigation with adrenaline is thought to be of benefit in this respect, and is used by some surgeons but not others. This prospective double blind controlled trial assessed the efficacy and safety of using perioperative adrenaline during extracapsular cataract surgery, as an adjunct to preoperative topical mydriatics. Seventy patients were randomised to receive intraocular irrigation fluid with or without 1:1,000,000 adrenaline. The adrenaline entering the eye through the anterior capsulotomy needle helped to resist the miosis induced by expression of the nucleus (7.1 versus 6.5 mm). The mydriasis maintained during irrigation aspiration was significantly greater in the group receiving adrenaline (6.6 versus 6.0 mm, p < 0.02). Their pupil diameters were also significantly larger at 20 minutes (p < 0.001) and 30 minutes (p < 0.01) into surgery. Pupillary constriction to a diameter of less than 5 mm occurred more frequently in the group not receiving adrenaline. Pulse rate and blood pressure in the 27 patients who had local anaesthesia showed no significant difference between the treatment groups (p > 0.05), and there was no significant variation from baseline (p > 0.05). Intraocular irrigation with adrenaline 1:1,000,000 is a safe and effective means of maintaining mydriasis during cataract surgery.

Intraocular dapiprazole for the reversal of mydriasis after extracapsular cataract extraction with intraocular lens implantation. Part II: Comparison with acetylcholine

Intraocular dapiprazole for reversing mydriasis during extracapsular cataract extraction with intraocular lens (IOL) implantation has been compared to intraocular acetylcholine. Ninety patients were enrolled in a double-blind study and divided into three groups of 30 eyes; each group received balanced salt solution (control), 0.25% dapiprazole, or 1% acetylcholine. Pupillary diameter recordings were performed immediately before and a few minutes after drug injection, and two, four and eight hours after surgery. Goldmann tonometry was performed the day before and 6 and 24 hours after surgery. Contact endothelial cell count was performed before and one and four months after surgery. The results indicated a slower starting but longer lasting effect with dapiprazole than with acetylcholine and a significant reduction of the postoperative intraoperative pressure rise with both drugs. No significant difference in reduction in the endothelial cell count was seen between dapiprazole and acetylcholine groups and the control group.

Clinical evaluation of the effect of acetylcholine on the corneal endothelium

A transient corneal edema is often seen after the injection of acetylcholine solution in the anterior chamber during cataract surgery. Ninety eyes of 90 patients scheduled for extracapsular cataract extraction with posterior chamber intraocular lens implantation were randomly assigned to two groups: one which received acetylcholine solution in the anterior chamber and one, a control group, which received only external conjunctival pilocarpine drops as a miotic. At three days, endothelial folds (P = .04) and corneal edema (P = .01) were more pronounced in the acetylcholine group; at seven days, endothelial folds were more severe (P = .04) in the acetylcholine group. At 30 days, the acetylcholine group showed a 37.2% increase (P = .01) of the endothelial cell area, whereas the control group showed a 7.08% increase. The difference between the groups was statistically significant (P = .05). Anterior chamber fluorophotometry at 30 days showed an increase of the corneal transfer coefficient that was higher but not significant in the acetylcholine group. We suggest caution in the intraoperative use of acetylcholine solution, particularly in those eyes showing a preoperative compromise of the endothelium.

Comparison of intraocular acetylcholine and carbachol

Commercially available 1% acetylcholine chloride and 0.01% carbachol chloride, which are commonly used as miotics in intraocular surgery, have recently been reformulated. Comparative studies of these agents show similar miotic activity. However, in vitro perfusion of human corneas demonstrated that 1% acetylcholine chloride causes marked changes in endothelial function and ultrastructure as compared to carbachol or BSS Plus. This study showed that 0.01% carbachol chloride was less toxic to the corneal endothelium than 1% acetylcholine chloride and suggests that 1% acetylcholine should not be used in corneas with compromised endothelium as in primary corneal endotheliopathies.

Endothelial physiology and intraocular lens implantation

The endothelium is the cellular monolayer which lines the posterior surface of the cornea. This layer is important in clinical ophthalmology because it is vital to maintenance of the transparency of the cornea and vision through its pump and barrier functions which limit the ingress of fluid into the cornea from the aqueous. When the function of the corneal endothelium becomes compromised, the corneal stroma swells as it hydrates. Subsequently, epithelial bullae form with painful recurring epithelial erosions, and finally corneal scarring and blindness result. The relatively vulnerable position of the corneal endothelium renders it susceptible to iatrogenic injury during intraocular procedures, especially IOL implantation: the poor regenerative (mitotic) capacity of the human corneal endothelium limits its ability to recover normal function once it is injured.