Definition

An abnormal increase in the internal pressure of the eye, which results in optic nerve atrophy and blindness.

Clinical Signs

May observe any of the following:

• Usually of rapid onset
• Unusual amount of blinking with pain
• Mild swelling or bulging of the eye
• Opaque or hazy cornea
• Ocular discharge (watery eye)
• Presence of conjunctivitis, uveitis, and/or dilated pupil

*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.

Etiology

Glaucoma is a group of diseases of the eye that causes increased intraocular pressure. The fluid produced by the eye, called aqueous humor, is normally kept in a balanced state and maintains the shape of the eye. It is when this balance of fluid shifts and more fluid is formed than is able to drain, that the pressure inside the eye begins to build. This increase in pressure causes damage to the retina, and the optic nerve, and results in blindness, if left untreated. Rats, fortunately rely little on eyesight, using their other senses more effectively to maneuver in their environment. However, any eye condition that results in pressure and or pain is considered a true emergency.

There are two classified forms of glaucoma, primary and secondary. In the primary form, pressure in the eye increases without previous disease, and may be a result of genetic predisposition. It tends to affect both eyes but may not occur at the same time.

With the secondary form of glaucoma, increased pressure is due to diseases such as diabetes, neoplasias (tumors), inflammation such as uveitis, ocular bleeding, or injury. Secondary glaucoma can affect one or both eyes, and is considered the one most often seen with rats.

It is important to try and seek treatment early in the disease, since increasing pressure and pain may result in having to have the eye removed.

Figure

Case History of Glaucoma

• Fig 1: Secondary glaucoma in 3-month-old male rat (Gogol)
• Fig 2: Glaucoma in 15-month-old female rat (Tepeu)
• Fig 3: Buphthalmos (congenital glaucoma) in female rat (Fai). This is a primary form of glaucoma.

 

Diagnostics

Obtain history from owner if possible. This is helpful in trying to determine and treat any underlying causes.

Visualization of the optic nerve with ophthalmoscopy. May see decrease in the retinal vascularity.

Tonometry (to test pressure in eye). An increased pressure may be indicative of glaucoma.

*Note: normal eye pressure in rats ranges between 21 to 26.¹

Treatment

Medications used to treat glaucoma in rats include the following:

• Trithalmic/Cortisone Ophthalmic Ointment applied to affected eye(s) once daily.
• Pilocarpine Ophthalmic Solution 1% to be applied to affected eye(s) twice daily, reducing to once daily as appropriate.

In the event uveitis is present, corticosteroids such as prednisone, or dexamethosone may be used systemically or topically.

In the absence of uveitis, NSAIDs such as: aspirin, or ibuprofen, flunixin meglumine, may be seen used.

In the event swelling and pain persist, enucleation (surgical removal of eye) of the eye should be a consideration.

If surgery is required, the following recommended post-op analgesia may be given:

• For severe pain or first 24 hours post-op: Buprenex (buprenorphine), or Torbugesic (butorphanol).

• For mild to moderate pain : Banamine (flunixin meglumine), Metacam (meloxicam), or carprofen. Do not use if a corticosteroid has already been prescribed.
• *Note: for pain not controlled by the use of an NSAID (e.g., Banamine, meloxicam, or carprofen), alone, consider alternating or co-administering with a narcotic (e.g., buprenorphine or butorphanol) or narcotic-like (e.g., tramadol) medication.

For information regarding medications refer to the Rat Medication Guide.

Nursing Care

• Provide for safe environment. Reduce chances of falls from heights by keeping cage levels to a minimum.
• Allow the rat to become familiar with cage surroundings. Prevent redesigning or moving interior cage accessories around.
• Keep water bottles and food dishes in same familiar area of cage.

Provide post-op care, as listed below, in event of surgical removal of eye:

• Provide hospital cage during recovery, especially if there are concerns that their cage mates may groom sutures or wound site.
• Provide clean bedding daily such as felt, soft t-shirt type material or ink-free paper towels. Avoid using material such as terry cloth type towels that can ravel. Also avoid litter-type bedding, post-op, until healed to prevent the chance of wound contamination or infection.
• Provide additional warmth to maintain body temperature within normal limits. It is essential that the rat does not become overheated or dehydrated. The rat should also be able to move away from the heat source if it becomes uncomfortable. If the rat is unconscious or immobile extreme care must be taken to keep the heat low and stable.
  • You can use an isothermic product that is heated in the microwave such as SnuggleSafe®. Make sure to follow the product directions carefully and wrap in a towel before placing in the cage. SnuggleSafe® will provide heat for 12 hours before needing to be reheated. Other similar types of products may vary in re-heat time. Check directions for individual product.
  • If using a heating pad (good for long term use) use only the low heat setting, put a thick towel in between the pad and the cage bottom, and place beneath a corner of the cage.
  • If none of these options are available you can use a plastic bottle filled with hot water, and wrapped in a towel, in the corner of the cage.
• Medicate for post-op pain as needed.
• Provide high calorie foods or food supplements such as Nutri-Cal Paste, canned Ensure, soy or soy formula, during recuperation.
• Encourage fluid intake while recuperating, such as water, Jell-O water, or electrolyte replacement drinks such as Pedialyte or Gatorade (which can be found in local grocery stores).
  • Please note that Pedialyte is only good refrigerated for 24 hours after opened, but can be frozen as ice cubes and thawed as needed.
  • *Note: juicy types of fruit also provide an additional fluid source in the diet.
• Contact veterinarian if any of the following are observed: swelling, redness, or pain at the incision site.

Outcome

• Pain, pressure, swelling reduced with meds
• Uneventful recovery if surgery required
• Free from signs of infection

Prevention

• Doing weekly assessments of rat’s health and becoming familiar with what the rat’s normal appearance is in order to detect change in appearance or condition early.
• Treat any underlying illnesses or infections promptly and appropriately.

Consultation and Technical Assistance

1. Dr. James Bogan, DVM, Banfield Veteranary Hospital of Waterford Lakes, Orlando. Normal range of eye pressure in rats.