Muro 128 (Bausch & Lomb) is an over-the-counter, hyperosmotic eye drop and ointment used to reduce corneal edema. I usually write a prescription so the pharmacist will provide instructions for usage. Occasionally, the patient's health insurance will pay for Muro 128 when an over-the-counter agent is written as a prescription.

This hyperosmotic is very effective at eliminating fluid from the corneal epithelium. So, it is important to understand when Muro 128 will be useful and when it will have no affect on corneal edema.

Muro 128 is available in 2% and 5% drops and in a 5% ointment. The drops come in 15-mL and 30-mL bottles, and the ointment is available in a 3.5-g ophthalmic tube dispenser. The 2% drops are preserved with methylparaben 0.046% and propylparaben 0.02%. The 5% solution has a 0.023% and 0.01% concentration of the preservatives, respectively. The drops should be stored at 59°F to 86°F. The primary component is sodium chloride (salt water).

What it will not do

Points to consider

Muro 128 stings upon instillation. Only epithelial edema is reduced. Wait a few days before starting treatment after a corneal abrasion. Microcysts will not be eliminated by a hyperosmotic. Stromal edema caused by endothelial cell loss is not improved with a hyperosmotic. Treatment lasting 6 to 8 weeks is usually needed to eliminate epithelial edema causing recurrent erosions. Instruct patients to instill a ribbon of ointment in the lower fornix, about ½-inch long, at bedtime. Muro 128 is safe to use for long periods of treatment.

Muro 128 will not eliminate corneal edema caused by extended wear contact lenses and endothelial dysfunction such as Fuchs' dystrophy. Striae or endothelial folds induced by stromal edema are not affected by hyperosmotics. Muro 128 seems to effectively eliminate edema only above the anterior limiting membrane of the cornea.

During the healing process after fingernail scratches, paper cuts and tree branch abrasions, the epithelium often does not reattach firmly to the anterior limiting membrane, resulting in edema in this area. Recurrent erosions often occur at these sites when the patient awakens. Many times, the area has re-epithelialized by the time the patient has arrived at your office.

The area sometimes will exhibit an area of negative stain when fluorescein is instilled. This is caused by the epithelium being elevated over the site from edema. Microcysts may also be present at the site of the recurrent erosion. These clinical signs are often not present, making it difficult to determine the location or if the patient truly had a recurrent erosion.

A good patient history is helpful in these situations. Has the patient suffered any eye injuries during the past year? Does the pain occur when the patient wakes up in the morning? Has it happened before? How long does it last?

If the symptoms and history lead you to believe that a recurrent erosion has occurred, I have found (by accident) an observation method to locate the edema area and to monitor the site to see if Muro 128 is resolving the edema: stand about 20 to 24 inches from the patient and hold your direct ophthalmoscope at a 45° angle to the apex of the patient's cornea. Focus the light on the anterior cornea. You will see a dark shadow in the anterior cornea at the location of the edema. It reminds me of the corneal shadow I see when viewing a low-grade keratoconic cornea with a direct ophthalmoscope. As treatment with the hyperosmotic progresses, the shadow will slowly decrease in size. When the shadow is gone, you can taper the Muro 128, and the patient will usually not experience a recurrence.

If the shadow does not go away with hyperosmotic treatment, a more aggressive therapy such as stromal puncture or phototherapeutic keratectomy (PTK) may be required. A bandage soft contact lens will infrequently help alleviate the recurrent erosion. This treatment is most often successful when a foreign body or eyelid disease is causing the epithelial erosion.

Deeper tissue unaffected

A hyperosmotic produces an osmotic force that moves the fluid from tissues with fewer sodium chloride ions to a fluid with a greater number of sodium chloride ions. This action is limited by distance and barriers. Deeper tissue, especially tissue protected by barriers such as epithelium, is not easily influenced by the hyperosmotics, so Muro 128 provides the greatest benefit for patients with epithelial edema.

Epithelial microcysts do not seem to resolve any more quickly when using a hyperosmotic. They will take about 6 weeks to totally resolve after extended-wear contact lenses are removed. My experience has been that it takes the same amount of time for microcysts to resolve, whether a hyperosmotic is used or not. It takes the corneal epithelium about 6 weeks to totally replicate itself, and that is how long it takes for the deep microcysts to disappear.

Treating map dot dystrophy

Patients with anterior basement membrane disease (map dot dystrophy) often have subtle decreases in vision and mild discomfort that is difficult for them to describe. They will have vague complaints of irritated eyes and vision that is not as sharp as it used to be. After ruling out refractive changes, cataract or macular degeneration, consider edema induced by the corneal dystrophy. These patients often exhibit mild epithelial fluorescein staining, negative staining and more advanced map dot dystrophy on slit lamp observation. Corneal topography provides helpful information regarding the irregularity of the corneal surface. Treating these patients with Muro 128 5% drops twice daily during the day and ointment at night will often improve vision and comfort.

Dry eye treatment may also be beneficial. Artificial tears or punctal occlusion can be helpful additive treatments for patients with map dot dystrophy. Negative staining and low tear volume, accompanied by symptoms of burning and stinging, are diagnostic of dry eye. Treatment for dry eye and map dot dystrophy may require the addition of punctal occlusion of the lower punctum. If the symptoms persist and tear volume is still inadequate, progress with occlusion of the upper punctum. Treating the dry eye with occlusion and the corneal edema with Muro 128 5% usually offers the patient noticeable improvement in comfort.

Treatment that is too aggressive following a corneal abrasion may result in sloughing of the new epithelium over the abrasion site. Young cells are loosely attached to the anterior limiting membrane, and sudden osmotic changes can result in loss of the new epithelial cells. I have found it best to wait 2 to 4 days after the epithelium has covered the wound before starting the patient on the hyperosmotic drops and ointment. This allows the cells to attach firmly, reducing the chance of re-abrading the corneal epithelium.

Other treatment options

When treating recurrent erosions, I prescribe Muro 128 5% drops four times a day and 5% ointment at bedtime for 2 weeks. Then, I re-evaluate the area of edema. Treatment may be necessary for up to 8 weeks to resolve the edema. Supportive treatment would include nonpreserved lubricating drops four times a day during the course of treatment. If the edema and recurrent erosions persist, it may be necessary to consider stromal puncture, oral doxycycline or PTK to solve the problem.

When treating anterior basement membrane disease (map dot dystrophy), my treatment plan varies according to the severity of symptoms. For patients who have mild to moderate symptoms, I prescribe Muro 128 5% drops twice a day and 5% ointment at bedtime for 4 weeks. Then, I re-evaluate to determine if a maintenance dose is required or if treatment can be stopped.

For moderate to severe symptoms associated with map dot dystrophy, I prescribe Muro 128 5% drops four times a day and 5% ointment at bedtime for 4 weeks. Then, I reduce the drop to twice daily while maintaining the ointment for another 4 weeks. At the end of 8 weeks, I re-evaluate patients to decide if maintenance therapy is needed. I often maintain these patients on Muro 128 5% twice a day and ointment at bedtime indefinitely. Nonpreserved lubricants and punctal occlusion are often helpful. PTK is an option if the epithelium is very irregular and when patient comfort and visual acuity are too compromised.

Recurrent erosions from injuries are common in primary eye care practices today. A safe, inexpensive initial treatment option such as Muro 128 often allows practitioners to provide patients with comfort without the risk potential and expense of stromal puncture, oral doxycycline or PTK.

For Your Information:

• Muro 128 is available from Bausch & Lomb, One Bausch & Lomb Place, Rochester, NY 14604-2701.