Chapter 28
Hyperosmotic Agents
JOHN DANIAS, JANET B. SERLE and DONNA J. GAGLIUSO
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HISTORICAL PERSPECTIVE
MECHANISMS OF INTRAOCULAR PRESSURE REDUCTION
PHARMACOLOGY
CLINICAL USES
SYSTEMIC SIDE EFFECTS AND CONTRAINDICATIONS
SUMMARY
REFERENCES

Systemically administered hyperosmotic agents are indicated in the treatment of acute, substantial elevations of intraocular pressure (IOP). They are most effective and best tolerated when used for a short time. Side effects and a limited duration of IOP-lowering response preclude chronic use in the treatment of glaucoma. Topically administered hyperosmotic agents are helpful in patients with edematous corneas. Transient dehydration of the cornea after topical administration allows for improved anterior and posterior segment visualization.
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HISTORICAL PERSPECTIVE
Various hypertonic substances have been used to reduce IOP and to treat cerebral edema. Agents that were used before 1956 included orally administered sodium chloride and lactose and intravenously administered glucose, sucrose, sodium chloride, sorbitol, and gum acacia.1,2 These agents were relatively ineffective because of their rapid distribution into total body fluids or were too toxic to be used clinically. In 1956, Javid and Settlage3 reported that intravenously administered urea effectively reduced intracranial pressure. In 1959, Galin and coworkers4 reported that intravenously administered urea was effective in reducing IOP. Subsequently, intravenously administered mannitol in 1962,5,6 orally administered glycerol in 1963,7 and orally administered isosorbide in 19678 were found to be effective hyperosmotic agents.
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MECHANISMS OF INTRAOCULAR PRESSURE REDUCTION
Two mechanisms are responsible for the decrease in IOP caused by hyperosmotic agents. The primary mechanism is a reduction in vitreous volume. Administration of hyperosmotic agents leads to hyperosmolality of the intravascular fluid. A bloodvitreous osmotic gradient is established (as effective drugs penetrate slowly into the avascular vitreous, and transport into the eye of hyperosmotic agents is restricted by the blood-ocular barrier). Fluid subsequently is drawn out of the vitreous into the vascular space, driven by this hyperosmotic gradient. This loss of fluid reduces the vitreous volume. A reduction in the vitreous volume leads to a reduction in IOP as the intraocular volume decreases while the scleral wall maintains a stable ocular shape and size. Studies performed in rabbits suggest that a 3% to 4% reduction in vitreous body weight occurs after administration of hyperosmotic agents in dosages comparable to those of clinical use.9 If an osmotic gradient cannot be established or maintained, then hyperosmotic agents cannot reduce IOP. This would occur if the blood-ocular barrier was not intact or if the agent used was not excluded by the normal barrier. A rebound elevation in IOP after the use of hyperosmotic agents may occur if the blood-ocular barrier is disrupted and hyperosmotic agents enter the intraocular space or if the osmotic pressure of the dehydrated vitreous becomes greater than the serum osmolality (e.g., by increased water consumption). Either of these situations causes a reversal of fluid flow from the intravascular space into the vitreous body.

Clinical and laboratory studies suggest that another secondary mechanism may play a small role in the IOP reduction seen with hyperosmotic agents. Oral or intravenous administration of low doses of hyperosmotic agents that do not increase serum osmolarity does reduce IOP.10,11 In animals with unilateral optic nerve transections, the operated eyes show reduced or absent IOP effects after low doses of hyperosmotic agents. In contrast, the eyes with intact optic nerves show IOP reductions after these low doses of hyperosmotic agents. Injection of hyperosmotic agents into the third ventricle of rabbits lowers IOP only in the eyes with intact optic nerves.10 These studies support the theory that a hypothalamic center with osmoreceptors and efferent connections to the eye mediates part of the IOP responses to hyperosmotic agents.

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PHARMACOLOGY
An osmotic gradient is a function of the difference of number of molecules (not the individual size of the molecules) in two solutions that are partitioned by a semipermeable membrane. A thousand molecules of a low-molecular-weight substance are just as effective as a thousand molecules of a highmolecular-weight substance, provided that both substances are equally excluded by the membrane. In the case of an hyperosmotic agent, the duration and effectiveness of an osmotic gradient are inversely dependent on the leakiness of the membrane separating the vascular and vitreous compartments and the rate at which the osmotic agent is cleared from the blood (by excretion or metabolism) and are directly dependent on how rapidly the substance enters the bloodstream.

The larger the number of molecules, the more hypertonic a solution. Thus, assuming all else is equal, on a per-gram basis, substances of lower molecular weight are more effective than substances of higher molecular weight (at the same dosage). Drugs with poor solubility require greater volumes of fluid for administration and are thus less effective in increasing intravascular osmolality.

Ocular penetration is a function of the permeability of the blood-ocular barrier and the size of the molecule. Larger molecules usually are more restricted in penetrating the blood-ocular barrier than are smaller molecules. The blood-ocular barrier has multiple components. The pigment epithelium of the iris and ciliary body forms the blood-aqueous barrier. More posteriorly, the retinal pigment epithelium forms a barrier between the choroidal circulation and the outer visual retina. The endothelial cells of the retinal vessels and capillaries form a barrier between the retinal circulation and the vitreous cavity on one side and the inner retina on the other side. The blood-aqueous barrier typically is leakier than the blood-retinal-vitreous barriers. This difference becomes more marked as the water solubility of a molecule increases and less marked as the lipid solubility increases. Fluid moves from the compartment of lower osmolarity. Systemically administered hyperosmotic agents increase intravascular osmolarity and induce fluid to flow out of the eye. The opposite flow of fluid (into the eye) was used in the water provocative test, which is of historical interest, and was used to diagnose glaucoma. Rapidly drinking a liter of water decreased the blood osmolarity. The relatively higher intraocular osmolarity induced the flow of fluid into the eye, raising the IOP.12 Finally, the route of administration dictates the onset of action of hyperosmotic agents. Intravenous administration is the most rapid route for accession of substances into the bloodstream and provides the most rapid onset of action.13

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CLINICAL USES

SYSTEMICALLY ADMINISTERED

Hyperosmotic agents that lower IOP are administered orally or intravenously in clinical practice (Tables 1 and 2). Indications for the use of hyperosmotic agents include the treatment of acute elevations in IOP and the treatment of glaucomas with critically shallow anterior chambers.

 

TABLE 1. Orally Administered Hyperosmotic Agents in Clinical Use


Generic NameTrade NameDosageDuration of ActionSide Effects (Agent-Specific)
GlycerolOsmoglyn50% solution 1---1.5 g/kg4---5 hrHyperglycemia/glycosuria Caloric loadNausea/vomiting
IsosorbideIsmotic45% solution 1.5---2 g/kg3.5---4.5 hrNausea/vomiting

 

 

TABLE 2. Intravenously Administered Hyperosmotic Agents in Clinical Use


Generic NameTrade NameDosageDuration of ActionSide Effects (Agent Specific)
UreaUreaphil30% solution 2---7 ml/kg (freshly prepared)5---6 hrThrombophlebitisTissue necrosisTemporary increase in BUN
MannitolOsmitrol10% or 20% solution 1---1.5 g/kg at rate of 3---5 ml/minUp to 6 hrAllergic reactionBUN = blood-urea nitrogen.

 

Elevations in IOP often are present before surgery in patients undergoing filtration surgery and the surgeon is concerned that the sudden drop in IOP occurring when the initial incision is made may cause problems such as choroidal hemorrhage. To avoid this problem, a hyperosmotic agent may be administered intravenously just before surgery. When the pressure has been reduced to a level that the surgeon considers safe for the patient to open the eye, surgery is begun.

Postoperative IOP elevations occur after various types of intraocular surgery, and hyperosmotic agents may be used to temporize. Significant IOP elevations occur in up to 20% of patients undergoing anterior segment laser surgery, including laser trabeculoplasty, laser iridectomy, and laser capsulotomy.14–16 The acute use of topical alpha adrenergic agonists such as apraclonidine (Iopidine) and brimonidine (Alphagan) before and after laser treatment has reduced the incidence of these IOP spikes,17–19 thereby reducing the need for hyperosmotic treatment after laser surgery. More recently, these alpha adrenergic drugs have been used in the chronic management of glaucoma.19–21 This renders them less effective in preventing and treating acute IOP elevations in patients treated with them chronically.22 The use of hyperosmotic agents after laser surgery may, therefore, increase.

Hyperosmotic agents are indicated in patients with secondary glaucomas including traumatic glaucoma, uveitic glaucoma, and neovascular glaucoma during acute episodes of IOP elevations. The short-term use of these agents may help patients avoid glaucoma surgery or allow for surgical intervention under more controlled circumstances.

Ocular diseases that lead to critical shallowing of the anterior chamber include pupillary block angle closure glaucoma and the various types of ciliary block glaucoma. In angle closure and ciliary block glaucomas, hyperosmotic agents not only lower the IOP but also deepen the anterior chamber. The reduction in vitreous volume allows the lens and iris to move posteriorly and the anterior chamber angle to open in patients without peripheral anterior synechiae. Hyperosmotic agents are not the definitive treatment for these conditions. Iridectomies are indicated to prevent repeated attacks of pupillary block angle closure glaucoma. Patients diagnosed with ciliary block glaucoma may need to be treated chronically with long-acting mydriatic agents such as atropine and scopalomine. Peripheral iridoplasty may be indicated in patients with variants of ciliary block glaucoma that are due to swelling or forward movement of the ciliary body, which may follow retinal detachment surgery, panretinal photocoagulation, and central retinal vein occlusion.

TOPICALLY ADMINISTERED

Topical hyperosmotic agents are used to dehydrate edematous corneas to improve the view of the anterior and posterior segments and to permit gonioscopic examination (Table 3). These agents are particularly useful in diagnosing suspected angle closure glaucoma in patients with elevated IOPs and cloudy corneas.

 

TABLE 3. Topically Administered Hyperosmotic Agents for Corneal Dehydration


Generic NameTrade NameConcentrationDuration of ActionSide EffectsUse
Sodium chlorideMuro 128Adsorbonac ophthalmicAK-NaCl5% (solution and ointment)2%, 5% solution5% (solution and ointment)Up to 7 hoursOccasional mild burningTherapeutic
GlycerinOphthalgan 1–5 minIntense burningDiagnostic

 

In addition, topical hyperosmotic agents are used chronically to dehydrate corneas in patients with failing endothelial function (e.g., patients with Fuch's dystrophy, postsurgical corneal decompensation). Topical agents in the form of drops or ointments improve corneal clarity and, thus, visual acuity in the early stages of corneal decompensation, often delaying the need for surgical intervention (see Table 3).

HYPEROSMOTIC AGENTS

Intravenous Agents

Hyperosmotic agents should be administered intravenously when the patient needs to be fasting, such as before surgery, or when the patient is nauseous or vomiting and is unable to take the agents orally. Intravenous agents have a faster onset of action than orally administered hyperosmotic agents.

Urea

Urea was first introduced into clinical practice in 1956 for neurosurgical use.3 Subsequently, in 1959, it was reported to be an effective ocular-hypotensive agent.4,23 Urea is administered as a 30% solution that must be freshly prepared. Stale solutions decompose to ammonia, a toxic byproduct. The recommended dosage is 2 to 7 ml/kg. IOP reductions occur within 30 to 45 minutes and peak at 1 hour after administration. Persistent reductions in IOP are observed for 5 to 6 hours. Urea is a small molecule6 and is not restricted to the extracellular or intravascular fluid compartment. It moves freely throughout total body water. Urea thus is less effective than mannitol for reducing IOP in inflammatory glaucomas. In addition, extravasation of urea during administration leads to tissue necrosis and sloughing; thus, the drug must be administered carefully. Urea is not metabolized and is excreted rapidly by the kidneys.24 The blood urea nitrogen level remains elevated for up to 6 hours after administration but returns to normal within 24 hours.25

Mannitol

Mannitol was first reported to be an effective ocular-hypotensive agent in 1962.6 Mannitol is administered as a 10% or 20% solution. It is stable in solution but is soluble only up to a concentration of 15% in cold water. If crystals are observed before administration, the solution can be warmed. A blood filter should also be used to avoid the entry of crystals into the bloodstream. The recommended dosage is 1 to 1.5 g/kg of body weight administered at a rate of 3 to 5 ml/min. IOP reductions occur within 30 to 45 minutes and peak 1 to 2 hours after administration. Persistent IOP reductions have been reported for up to 6 hours.26 Mannitol is eliminated by the kidneys and is not metabolized in the body.24 The large size of the molecule prevents it from crossing the intact blood-ocular barrier.24

Oral Agents

Oral agents have the advantages of less-systemic toxicity than intravenously administered agents, and they can be administered on an outpatient basis, thus eliminating the need for obligatory hospitalization.27 However, oral administration of hyperosmotic agents may be accompanied by unpleasant gastrointestinal side effects.

Glycerol

Glycerol was the first oral hyperosmotic agent to be used clinically.7 Glycerol is available as a 50% solution in 0.9% saline. One milliliter of this solution contains 0.62 g of glycerol. Dosages used in clinical practice range between 1 and 1.5 g/kg of body weight. The taste is not very pleasant (extremely sweet), so orange juice or ice can be used to make glycerol more palatable.

Orally administered glycerol is not as effective as intravenously administered hyperosmotic agents in lowering IOP. Absorption is variable and glycerol crosses the blood-aqueous barrier in the inflamed eye more easily than other hyperosmotic agents.25 The advantage of glycerol is that it is a component of human body fat, as it constitutes approximately 1% of body weight. Glycerol thus is readily metabolized, which makes it relatively safe. Accidental ingestion of up to 23 g/kg in a 2½-year old was tolerated.28 Experimental chronic oral administration of approximately 1 to 3 g/kg three times a day for 7 weeks in 14 humans produced no significant toxicity.29 Glycerol is metabolized through the tricarboxylic acid cycle to glucose, and hyperglycemia and glycosuria can result from its use. Thus, it is relatively contraindicated in subjects with diabetes as it can easily upset glucose control. The high concentration of glucose after metabolism of glycerol also provides a substantial caloric load in contrast to the other clinically available hyperosmotic agents. Interestingly, in the preinsulin era, glycerin was used as a source of carbohydrate in subjects with diabetes as its cellular uptake does not require insulin.

The onset of the ocular-hypotensive effect of glycerol is 10 minutes after administration and the peak effect is 30 minutes to 1 hour after administration. The duration of IOP reduction is 4 to 5 hours, after which IOP returns to pretreatment values. Glycerol administration can be repeated at that time.7 As the drug is metabolized, it is less likely to produce a diuresis than a nonmetabolized drug such as isosorbide or mannitol. This may be useful for surgery in which the surgeon wishes to avoid the need for a Foley catheter.

Isosorbide

Isosorbide was first used for lowering IOP in 1967.8 Since then, isosorbide has quickly surpassed glycerol as the oral hyperosmotic of choice in the United States. Its main advantage is rapid and almost complete absorption from the gastrointestinal tract.30 In addition, isosorbide is more palatable than glycerol, causing less nausea. Nonetheless, it is far from tasty and is most palatable when administered with ice or orange juice. Isosorbide is available as a 45% solution. Dosages used clinically range from 1.5 to 2 g/kg and produce IOP reductions comparable to clinically administered dosages of glycerol. However, isosorbide is not metabolized and does not cause hyperglycemia.

Maximum reductions in IOP occur 45 minutes to 2 hours after administration. IOP decreases by 25% to 90% and returns to pretreatment values in 3½ to 4½ hours after administration.31 Over 95% of a dose of isosorbide is excreted unchanged by the kidneys.32

Ethanol

Ethanol has been investigated as an IOP-lowering agent in both normotensive and glaucomatous patients at various doses.24,33 In relatively high doses, it decreases IOP through both an osmotic action on the vitreous (as penetration into the vitreous is slow) and by inhibition of secretion of antidiuretic hormone by the posterior pituitary gland. Unfortunately, intoxication associated with the use of ethanol precludes its use in clinical practice. The effective dosage as an osmotic agent is approximately 2 to 3 ml/kg of 40% to 50% (i.e., 80 to 100 proof) alcohol.

Urea

Urea has been administered orally, but it is not palatable. Thus, if selected, urea should be administered intravenously.

TOPICAL AGENTS

Glycerol

Glycerol (Ophthalgan) is used to clear the cornea to perform gonioscopy in patients with microcystic corneal edema (see Table 3). The effect on the cornea is only temporary (1 to 5 minutes). The onset of action is rapid (1 to 2 minutes). Topically applied hyperosmotic agents do not reduce IOP. They do not create a sufficient osmotic gradient, as they are quickly diluted by tears. Glycerol causes intense burning when applied to the nonanesthetized cornea; thus, topical anesthesia is indicated before its use.

Sodium Chloride

Sodium chloride 5% is available in both drops and ointment (see Table 3). It has no significant side effects except for occasional mild burning and irritation. When used as an ointment, sodium chloride 5% temporarily can blur the vision. Hypertonic sodium chloride in ointment form can reduce corneal thickness up to 24% in patients with compromised corneal endothelial function. The effect lasts up to 7 hours and is maximal 3 to 4 hours after application. In contrast, sodium chloride drops seem to have little effect on corneal thickness.34

Dextran Polysaccharide

The colloidal dextran polysaccharide solution (Dehydrex), which has been evaluated for use in patients with recurrent corneal erosion syndrome, is not commercially available.35 This solution is a high-molecular-weight polysaccharide that is equal to or slightly hyperosmolar to corneal tissues. One small clinical trial suggests this solution, which causes epithelial dehydration and lubrication, improves vision, and reduces symptoms in patients with recurrent corneal erosion syndrome.

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SYSTEMIC SIDE EFFECTS AND CONTRAINDICATIONS
The mechanism by which the systemically administered hyperosmotic agents reduce IOP (i.e., relative dehydration of extravascular spaces) also is the reason for the side effects of these agents. Water is drawn into the intravascular space, thus increasing the intravascular volume. This is relatively well tolerated in healthy individuals. However, it can be detrimental in patients sensitive to acute changes of intravascular volume, such as patients with chronic congestive heart failure. In these patients, the use of systemic hyperosmotic agents can induce an acute episode of heart failure.36 Headache is a common side effect of hyperosmotic agents. The headache is caused by cerebral dehydration, causing reduced intracranial pressure.37 It may last for as long as 45 minutes to 1 hour after administration of the agent. The headache is quite similar to headaches that occur after lumbar puncture. In a few patients, cerebral dehydration has caused confusion and disorientation.37 This is more common with intravenous agents that have a more rapid onset of effect.

Increased diuresis results from the use of systemic hyperosmotic agents as the intravascular volume expands. Many of the hyperosmotic agents are excreted in the urine, and catheterization may be necessary in anesthetized patients to avoid severe distention of the bladder.37 Urinary retention with severe bladder distention is common in older men with prostatic hypertrophy, particularly when they cannot void for extended periods such as during a surgical procedure.

Renal failure is a relative contraindication to the use of hyperosmotic agents. The fluid drawn into the intravascular space by these agents is excreted by the kidneys. If renal function is compromised, the increase in intravascular free water causes plasma sodium concentration to fall. The resulting hyponatremia can lead to lethargy, seizures, and coma.28 Potassium depletion also may occur. Renal toxicity can complicate the situation as many of these agents are excreted in the urine, and compromised renal function can reduce their elimination. In this situation, hemodialysis is indicated as neurologic deterioration can be rapid.36 Thus, in patients with compromised renal function, there is an advantage to using hyperosmotic agents that are metabolized as well as excreted, such as glycerin.

Nausea and vomiting are the most common side effects, particularly in patients receiving orally administered hyperosmotic agents. This side effect also has been reported in up to 30% of patients receiving urea intravenously.23 Severe vomiting can limit the usefulness of oral hyperosmotic agents in the preoperative treatment of patients.

Extravasation of urea during infusion can cause local tissue damage, which can be quite painful and rarely produces necrosis.38 Mannitol extravasation causes only localized swelling.5 In addition, thrombophlebitis at the site of injection is more common with urea and occurs in up to 5% of patients. Mannitol thrombophlebitis is extremely uncommon and very mild.6 Rare events that have been reported in association with the use of hyperosmotic agents include the development of subdural hematomas with urea39 and allergic reactions with mannitol.40,41

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SUMMARY
Hyperosmotic agents reduce IOP by increasing plasma osmolarity and thus drawing water out of the vitreous and into the intravascular space. Systemically administered hyperosmotic agents are indicated for the short-term management of acute elevations of IOP such as preoperative and early postoperative IOP elevations, and pupillary block and ciliary block glaucomas. These medications are indicated in the treatment of acute IOP elevations in patients nonresponsive to topically administered ocular hypotensive agents and systemically administered carbonic anhydrase inhibitors. Orally administered hyperosmotic agents are less toxic but may not be tolerated as well as intravenously administered agents. Intravenous agents have a more rapid onset of effect. Elimination of many of these agents is through the kidneys. The preferred hyperosmotic agents are mannitol for intravenous administration and isosorbide for oral administration. These two agents are better tolerated and induce fewer side effects than the other drugs currently available.

Hyperosmotic agents should not be administered chronically to treat glaucoma. The duration of IOP effect is relatively brief, 4 to 6 hours; thus, dosing three to four times daily would be required for chronic use. Repetitive dosing leads to decreased efficacy, as the hyperosmotic particles eventually enter the extravascular spaces. Rebound elevations of IOP have been noted after repetitive dosing. Side effects are quite common and occasionally serious. Thus, long-term use of hyperosmotic agents for the chronic management of glaucoma is not appropriate.

Topical hyperosmotic agents draw water from the cornea into the tears. They are useful diagnostic tools for temporarily clearing the cornea in cases of corneal edema, and they are useful therapeutic tools for the chronic management of mild cornea edema. Side effects of these agents are limited to local ocular discomfort.

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REFERENCES

1. Dyrr EW, Matthew WB: Use of sucrose preparatory to surgical treatment of glaucoma. Arch Ophthalmol 18:57–61, 1937

2. Bellows J, Puntenney I, Cowen J: Use of sorbitol in glaucoma. Arch Ophthalmol 20:1036–1043, 1938

3. Javid M, Settlage P: Effect of urea on cerebrospinal fluid pressure in human subjects: Preliminary report. JAMA 160:943–949, 1956

4. Galin MA, Futaba A, McLean JM: Urea as an osmotic ocular hypotensive agent in glaucoma. Arch Ophthalmol 62:347–352, 1959

5. Smith EW, Drance SM: Reduction of human intraocular pressure with intravenous mannitol. Arch Ophthalmol 68: 734–737, 1962

6. Weiss DI, Shaffer RN, Wise BL: Mannitol infusion to reduce intraocular pressure. Arch Ophthalmol 68:341–347, 1962

7. Virno M, Cantore P, Bietti C et al: Oral glycerol in ophthalmology. Am J Ophthalmol 55:1133–1142, 1963

8. Becker B, Kolker AE, Krupin T: Isosorbide: An oral hyperosmotic agent. Arch Ophthalmol 78:147–150, 1967

9. Robbins R, Galin MA: Effect of osmotic agents on the vitreous body. Arch Ophthalmol 82:694–699, 1969

10. Krupin T, Podos SM, Becker B: Effect of optic nerve transection on osmotic alterations of intraocular pressure. Am J Ophthalmol 70:214–220, 1970

11. Podos SM, Krupin T, Becker B: Effect of small-dose hyperosmotic injections on intraocular pressure of small animals and man when optic nerves are transected and intact. Am J Ophthalmol 71:898–903, 1971

12. McLean JM, Galin MA: The effect of reduced blood osmolarity on intraocular pressure. Trans Am Ophthalmol Soc 58:118–131, 1960

13. Feitl ME, Krupin T: Hyperosmotics. In Ritch R, Shields MB, Krupin T (eds): The Glaucomas, pp 1483–1488. St Louis: Mosby, 1996

14. Zborowski L, Ritch R, Podos SM et al: Prognostic features in laser trabeculoplasty. Acta Ophthalmol 62:142–149, 1984

15. Shani L, David R, Tessler L et al: Intraocular pressure after Nd-YAG laser treatments in the anterior segment. J Cataract Refract Surg 20:455–458, 1994

16. Slomovic AR, Parrish RK 2d: Acute elevations of intraocular pressure following Nd-YAG laser posterior capsulotomy. Ophthalmology 92:973–976, 1985

17. Lewis R, Perkins TW, Grangnon R et al: The rarity of clinically significant rise in intraocular pressure after laser peripheral iridotomy with apraclonidine. Ophthalmology 105: 2256–2259, 1998

18. Chevrier RL, Assalian A, Duperre J et al: Apraclonidine 0.5% vs brimonidine 0.2% for the control of intraocular pressure elevation following anterior segment laser procedures. Ophthalmic Surg Lasers 30:199–204, 1999

19. Walters JR: Development and use of brimonidine in treating acute and chronic elevations of intraocular pressure: A review of safety, efficacy, dose response, and dosing studies. Surv Ophthalmol 41(Suppl 1):S19–S26, 1996

20. Serle JB, the Brimonidine Study Group III: A comparison of the safety and efficacy of twice daily brimonidine 0.2% versus betaxolol 0.25% in subjects with elevated intraocular pressure. Surv Ophthalmol 41(Suppl 1):S39–S47, 1996

21. Schuman J: Clinical experience with brimonidine 0.2% and timolol 0.5% in glaucoma and ocular hypertension. Surv Ophthalmol 41(Suppl 1):S27–S37, 1996

22. Chung HS, Shin DH, Birt CM et al: Chronic use of apraclonidine decreases its moderation of post-laser intraocular pressure spikes. Ophthalmology 104:1921–1925, 1997

23. Tarter RC, Capt USAF Linn Jr JG: A clinical study of the use of intravenous urea in glaucoma. Am J Ophthalmol 52:323–330, 1961

24. Becker B, Kolker AE, Krupin T: Hyperosmotic agents. In Leopold IM (ed): Symposium on Ocular Therapy, pp 42–53. Vol 3. St Louis: Mosby, 1968

25. Galin MA, Davidson R, Shachter N: Ophthalmological use of osmotic therapy. Am J Ophthalmol 62:629–634, 1966

26. Adams RE, Kirschner RJ, Leopold IH: Ocular hypotensive effect of intravenously administered mannitol. Arch Ophthalmol 69:55–58, 1963

27. Kolker AE, Hetherington J Jr: Hyperosmotic agents. In Becker-Shaffer's diagnosis and therapy of the glaucoma, pp 408–411. St Louis, MO: Mosby, 1983

28. Thomas R: Glycerin. Arch Ophthalmol 70:625–628, 1963

29. Johnson V, Carlson AJ, Johnson A: Studies on the physiological action of glycerol on the animal organism. Am J Physiol 103:517–534, 1933

30. Krupin T, Kolker AE, Becker B: A comparison of isosorbide and glycerol for cataract surgery. Am J Ophthalmol 69:737–740, 1970

31. Mehra SK, Singh R: Lowering of intraocular pressure by isosorbide. Arch Ophthalmol 86:623–625, 1971

32. Troncale FJ, Shear L, Shinaberger JH et al: Isosorbide diuretic effect following oral administration to normal subjects. Am J Med Sci 251:188–193, 1966

33. Obstbaum SA, Podos SM, Kolker AE: Low-dose oral alcohol and intraocular pressure. Am J Ophthalmol 76:926–928, 1973

34. Luxenberg MN, Green K: Reduction of corneal edema with topical hypertonic agents. Am J Ophthalmol 71:847–853, 1971

35. Foulks GN: Treatment of recurrent corneal erosion and corneal edema with topical osmotic colloidal solution. Ophthalmology 88:801–803, 1981

36. Borges HF, Hocks J, Kjellstrand CM: Mannitol intoxication in patients with renal failure. Arch Intern Med 142:63–66, 1982

37. Havener WH: Osmotic agents. In Ocular Pharmacology, pp 440–463. St Louis, MO: Mosby, 1978

38. Davis M, Duehr P, Javid M: The clinical use of urea for reduction of intraocular pressure. Arch Ophthalmol 65:526–531, 1961

39. Marshall S, Hinman Jr F: Subdural hematoma following administration of urea for diagnosis of hypertension. JAMA 182:233–234, 1962

40. Spaeth GL, Spaeth EB, Spaeth PG et al: Anaphylactic reaction to mannitol. Arch Ophthalmol 78:583–584, 1967

41. McNeill IY: Hypersensitivity reaction to mannitol. Drug Intel Clin Pharm 19:552–553, 1985

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