Clinical History:

A 62-year-old woman has noted decreasing visual acuity in her peripheral vision over the past year, and she states that "everything just seems to be darker." She goes to her optometrist. The optometrist, using an "air puff" tonometer" discovers that she has increased intraocular pressure bilaterally. The cornea and sclera of each eye appear normal. There is no opacification of the crystalline lens.

Funduscopic and Microscopic Pathology:

There is cupping of the optic disk (images 4.1 and 4.2) as a consequence of the increased intraocular pressure, leading to atrophy of the optic nerve head. Image 4.3 illustrates the normal histology of eye structures that play a role in the pathophysiology of glaucoma. Image 4.4 demonstrates papilledema, which is seen with increased intracranial pressure.

Questions:

1. What condition is present? Who is at risk?

This is glaucoma. Older persons, black race, history of diabetes mellitus, and history of corticosteroid use increase the risk for glaucoma.

2. How is this condition detected?

Methods include tonometry (measuring intraocular pressure), funduscopy (viewing the retina; also called ophthalmoscopy), and perimetry (measuring visual fields). Tonometry is often performed with a device that is "non-contact" with the eye, using a puff of air to determine intraocular pressure. A more sensitive and exact measurement can be taken with a Goldmann applanation tonometer mounted on a slit lamp. Gonioscopy, utilizing a goniolens, can be used to view the angle of the anterior chamber to determine if "open angle" or "closed angle" glaucoma is present. However, not all persons with increased intraocular pressure will develop glaucoma, and not all persons with glaucoma have a measurable increase in intraocular pressure. Thus, it is recommended to screen patients by funduscopy and ophthalmoscopy (slit-lamp exam) as well as for pressure. Testing of visual fields (perimetry) may be indicated.

3. How does this condition occur?

There are several ways that intraocular pressure can be increased. The process is generally slow and painless, so the affected person is not often aware of the condition until substantial visual problems have occurred.

The drainage of the aqueous humor in the anterior and posterior chambers of the eye occurs at the angle of the ciliary body with the cornea, where a trabecular meshwork of veins leads to the canal of Schlemm. Eyes that are small and hyperopic (farsighted) have a narrower angle that reduces resorbtion of fluid, leading to the so-called "primary angle-closure glaucoma." There is a propensity for an acute exacerbation marked by intense pain and the appearance of halos around lights, as if looking through a steamy shower door. This is an emergency that must be immediately treated.

However, most cases of glaucoma (about 1 in 100 persons under age 65 and up to 1 in 25 persons over age 75) are of the "primary open-angle glaucoma" type in which there is no anatomic abnormality, but decreased resorbtion for an unknown reason. Persons with this condition tend to lose peripheral vision first and have a sensation that everything appears darker. In the U.S. persons of African-American ancestry develop this disorder more often than caucasians.

Much rarer are congenital glaucoma and glaucoma due to increased produced of aqueous. Signs of congenital glaucoma in an infant may include increased rubbing of eyes and a hazy corneal appearance.

4. How is this condition treated?

Both topical and systemic agents may be used. Topical beta-adrenergic receptor blocking agents such as timolol, topical carbonic anhydrase inhibitors such as dorzolamide, and alpha-2 adrenergic agonists such as brimonidine decrease the production of aqueous. An oral carbonic anhydrase inhibitor such as acetazolamide can be employed. Pilocarpine is a cholinergic parasympathomimetic agent that increases filtration or drainage out of the eye. Prostaglandin receptor agonists such as latanoprost also increase the outflow of aqueous humor. There are potential concerns about the systemic absorbtion of drugs, such as the beta-blockers in persons with asthma or diabetes mellitus.

Argon laser trabeculoplasty shrinks the trabecular meshwork and improves glaucoma in most cases of primary open angle glaucoma not responsive to drug therapy.

A surgical procedure called trabeculectomy involves excising a small section of the trabecular meshwork to create artificial filtration of aqueous, but the surgical site tends to scar and close to block fluid drainage after a few years.

5. What is the significance of the condition in image 4.4?

Papilledema indicates a medical emergency. The outward bulging of the optic nerve head at the optic disk indicates increased intracranial pressure which can presage herniation.


6. For a patient with significant visual impairment who continues to operate a motor vehicle, what should you do?

The best thing to do is tell the patient to be tested by the department of motor vehicles (DMV) and that this is important for their safety as well as others. State that their safety is part of your responsibility so if they don't contact the DMV, you will.

Typical visual requirements for operating a motor vehicle are: 20/70 vision in either eye, or both eyes together, with or without corrective lenses. If one eye is 20/200 or worse, the other eye must be 20/40 or better, with or without a corrective lens. 130 degrees is the minimum acceptable field of vision (normal is 180 degrees).

The types of problems that can impair ability to operate a motor vehicle include: seizure disorders or blackouts, dizzy spells, severe cardiovascular problems, memory or judgment impairment, drug or alcohol problems, progressive neurological disorders, severe psychiatric disorders, visual impairments, sleep disorders, poorly controlled diabetes mellitus, and severe head injuries.