Ординатура / Офтальмология / Английские материалы / Ophthalmology A Short Textbook_Lang_2000

10.3 Primary Glaucoma 253

Perimetry. Noise field perimetry is suitable as a screening test as it makes the patient aware of scotomas and makes it possible to detect and describe them. The patient is shown a flickering monitor displaying what resembles image noise on a television set. The patient will not see the flickering points in the region of the scotoma. After this test, the defect should be quantified by more specific methods. Automatic grid perimetry is suitable for the early stages of glaucoma. Special programs (such as the G1 program on the Octopus perimeter and the 30–2 program on the Humphrey perimeter devices) reveal the earliest glaucomatous changes. In advanced glaucoma, kinetic hand perimetry with the Goldmann perimeter device is a useful preliminary examination to evaluate the remaining field of vision.

Differential diagnosis: Two disorders are important in this context:

Ocular hypertension. Patients with ocular hypertension have significantly increased intraocular pressure over a period of years without signs of glaucomatous optic nerve damage or visual field defects. Some patients in this group will continue to have elevated intraocular pressure but will not develop glaucomatous lesions; the others will develop primary open angle glaucoma. The probability that a patient will develop definitive glaucoma increases the higher the intraocular pressure, the younger the patient, and the more compelling the evidence of a history of glaucoma in the family.

Low-tension glaucoma. Patients with low-tension glaucoma exhibit typical progressive glaucomatous changes in the optic disk and visual field without elevated intraocular pressure. These patients are very difficult to treat because management cannot focus on the control of intraocular pressure. Often these patients will have a history of hemodynamic crises such as gastrointestinal or uterine bleeding with significant loss of blood, low blood pressure, and peripheral vascular spasms (cold hands and feet). Patients with glaucoma may also experience further worsening of the visual field due to a drop in blood pressure.

Caution should be exercised when using cardiovascular and anti-hyper- tension medications in patients with glaucoma.

Treatment: Indications for initiating treatment.

Glaucomatous changes in the optic cup: Medical treatment should be initiated where there are signs of glaucomatous changes in the optic cup or where there is a difference of more than 20% between the optic cups of the two eyes.

Any intraocular pressure exceeding 30 mm Hg should be treated.

Increasing glaucomatous changes in the optic cup or increasing visual field defects: Regardless of the pressure measured, these changes show that the current pressure level is too high for the optic nerve and that additional medical therapy is indicated. This also applies to patients with advanced

254 10 Glaucoma

glaucomatous damage and threshold pressure levels (around 22 mm Hg). The strongest possible medications are indicated in these cases to lower pressure as much as possible (10–12 mm Hg).

Early stages: It is often difficult to determine whether therapy is indicated in the early stages, especially where intraocular pressure is elevated slightly above threshold values. Patients with low-tension glaucoma exhibit increasing cupping of the optical disk even at normal pressures (less than 22 mm Hg), whereas patients with elevated intraocular pressure (25–33 mm Hg) may exhibit an unchanged optic nerve for years.

Patients with suspected glaucoma and risk factors such as a family history of the disorder, middle myopia, glaucoma in the other eye, or differences between the optic cup in the two eyes should be monitored closely. Follow-up examinations should be performed three to four times a year, especially for patients not undergoing treatment.

Medical therapy. Available options in medical treatment of glaucoma (see also Fig. 10.1):

Inhibit aqueous humor production.

Increase trabecular outflow.

Increase uveoscleral outflow.

Fig. 10.14 and Table 10.3 list the various active ingredients and substance groups available for medical treatment of glaucoma. For the sake of completeness, Fig. 10.14 also lists traditional substances that are no longer used today; these include substances that have too many side effects or have been replaced by more efficient medications. Table 10.3 lists only those medications that are actually used today.

Principles of medical treatment of primary open angle glaucoma:

Medical therapy is the treatment of choice for primary open angle glaucoma. Surgery is indicated only where medical therapy fails.

There is no one generally applicable therapy plan. However, several principles may be formulated:

Where miosis is undesirable, therapy should begin with beta blockers (Table 10.3).

Where miosis is not a problem (as is the case with aphakia), therapy begins with miotic agents.

Miotic agents may be supplemented with beta blockers, epinephrine derivatives, guanethidine, dorzolamide and/or latanoprost maximum topical therapy).

Osmotic agents or carbonic anhydrase inhibitors (administered orally or intravenously) inhibit the production of aqueous humor. They can be administered temporarily in addition to topical medications. Their side effects usually make them unsuitable for prolonged treatment. The general rule is to try to use the weakest possible medications required to

phrine derivatives form deposits in the conjunctiva (adrenochrome deposits) and can lead to obstruction of the canaliculus (see Fig. 4.24 h).

episcleral venous pressure and reducing aqueous humor production by decreasing ciliary body perfusion.

Continued !

Continued !

Argon laser trabeculoplasty:

Principle: Laser burns in the trabecular meshwork cause tissue contraction that widens the intervening spaces and improves outflow through the trabecular meshwork.

Technique: Fifty to 100 focal laser burns are placed in the anterior trabecular meshwork (Fig. 10.15).

Comment: Laser surgery in the angle of anterior chamber is possible only if the angle is open. The surgery itself is largely painless, may be performed as an outpatient procedure, and involves few possible complications. These may include bleeding from vascular structures near the angle and synechiae between the iris and individual laser burns. Argon laser trabeculoplasty can bring improvement with intraocular pressures up to 30 mm Hg. It decreases intraocular pressure by about 6–8 m Hg for about two years. Argon laser trabeculoplasty is only effective in about every second patient. The full effect occurs about four to six weeks postoperatively.

262 10 Glaucoma

Argon laser trabeculoplasty.

Fig. 10.15 An argon laser beam is focused on the trabecular meshwork through a gonioscope and slit lamp. Approximately 100 laser burns are placed in a circle in the trabecular meshwork to improve aqueous humor drainage.

Filtration surgery:

Principle: The aqueous humor is drained through the anterior chamber through a subconjunctival scleral opening, circumventing the trabecular meshwork. Formation of a thin-walled filtration bleb is a sign of sufficient drainage of aqueous humor.

Technique (Fig. 10.16a – c): First a conjunctival flap is raised, which may be either fornix-based or limbal-based. Then a partial-thickness scleral flap is raised. Access to the anterior chamber is gained via a goniotomy performed with a 1.5 mm trephine at the sclerocorneal junction or via a rectangular trabeculectomy performed with a scalpel and dissecting scissors. A peripheral iridectomy is then performed through this opening. The scleral flap is then loosely closed and covered with conjunctiva.

Comment: A permanent reduction in intraocular pressure is achieved in 80–85% of these operations.

Cyclodialysis:

Principle: The aqueous humor is drained through an opening into the suprachoroidal space.

Technique: A full-thickness scleral incision is made down to the ciliary body 4 mm posterior to the limbus. The sclera is then separated from the