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Ophthalmology > INTRAOCULAR PRESSURE
Ocular Hypotony
Article Last Updated: Nov 12, 2007
AUTHOR AND EDITOR INFORMATION
Section 1 of 11  
Author: Sheila P Sanders, MD, Associate Professor, Director of Glaucoma Service, Department of Ophthalmology, University of Kentucky College of Medicine
Sheila P Sanders is a member of the following medical societies: American Academy of Ophthalmology and American Glaucoma Society
Editors: Bradford Shingleton, MD, Assistant Clinical Professor of Ophthalmology, Department of Ophthalmology, Harvard Medical School; Consulting Staff, Massachusetts Eye and Ear Infirmary; Simon K Law, MD, PharmD, Assistant Professor of Ophthalmology, Jules Stein Eye Institute; Chief of Section of Ophthalmology Surgical Services, Department of Veterans Affairs Healthcare Center, West Los Angeles; J James Rowsey, MD, Director of Corneal Services, St Luke's Cataract and Laser Institute, Florida; Lance L Brown, OD, MD, Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri; Hampton Roy Sr, MD, Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences
Author and Editor Disclosure
Synonyms and related keywords:
low intraocular pressure, choroidal detachment, wound leak, overfiltration, complication of glaucoma surgery, flat anterior chamber, cyclodialysis cleft, uveitis
Background
Hypotony is usually defined as an intraocular pressure (IOP) of 5 mm Hg or less. Low IOP can adversely impact the eye in many ways, including corneal decompensation, accelerated cataract formation, and maculopathy. Clinically significant changes occur more frequently as the IOP approaches 0 mm Hg.
Pathophysiology
The usual rate of aqueous humor production is 2.5 µL/min. According to traditional teaching, in healthy human eyes, about 90% of aqueous humor exits through the conventional trabecular meshwork/juxtacanalicular/Schlemm canal/episcleral venous route. The remaining 10% exits via the uveoscleral outflow, where it crosses the ciliary body, sclera, or scleral openings to reach the suprachoroidal space. Studies suggest that the percentage of uveoscleral outflow may actually be much higher. Flow through the trabecular route ceases when IOP declines below the episcleral venous pressure, usually 9 mm Hg. Therefore, uveoscleral outflow predominates at low IOPs. Hypotony occurs when aqueous humor production does not keep pace with outflow. Outflow may be greater than usual, as seen with wound leak, overfiltering bleb, or cyclodialysis cleft. Conditions that decrease ciliary body function, such as iridocyclitis, hypoperfusion, or tractional ciliary body detachment, may cause inadequate aqueous humor production. Hypotony is also seen in association with rhegmatogenous retinal detachments and some altered osmotic states. Inflammation plays a key role in the evolution of hypotony. It causes increased permeability of the blood-aqueous barrier. Choroidal fluid is believed to accumulate as a result of enhanced uveoscleral outflow and decreased aqueous humor production, a cycle that is often perpetuated once choroidal effusions develop. An anterior ring of choroidal fluid can rotate the ciliary body forward, impairing its ability to produce aqueous humor.
Frequency
United States
Hypotony following glaucoma surgery is common but often not clinically significant. Transient hypotony can be seen following other types of ocular surgery, especially if a pars plana approach has been used, or following trauma. The rate of hypotony following uncomplicated cataract surgery is extremely low. The incidence of hypotony following trabeculectomy increases with the use of antifibrinolytic agents. Chronic hypotony leading to phthisis is rare and occurs only in eyes with severe damage or complex problems.
Mortality/Morbidity
- Hypotony usually occurs as a complication of an underlying ocular disorder.
- Transient or permanent visual impairment may result from corneal changes, accelerated cataract formation, choroidal fluid, choroidal folds, maculopathy with disturbance of the retinal pigment epithelium (RPE), cystoid macular edema, or optic disc
k edema. - Hypotony in the setting of an incompetent corneal or limbal wound can predispose the patient to epithelial ingrowth.
- Severe chronic hypotony can ultimately lead to phthisis.
Sex
Females may be more predisposed to hypotony following antimetabolite-enhanced trabeculectomy. Males may be more prone to hypotony maculopathy.
Age
Young patients with myopia may be more predisposed to hypotony following trabeculectomy.
History
- Recent trauma or surgery, especially the following:
- Glaucoma surgery with antimetabolites, a loosely sutured trabeculectomy flap, or a large track created to introduce a tube shunt
- 25-gauge vitrectomy surgery
- Surgery requiring partial thickness scleral sutures, particularly in patients with myopia or abnormally thin tissue
- History of iridocyclitis
- Blurred vision
- Eye pain (usually a deep ache), especially with choroidal detachment (Hemorrhagic choroidal detachment can cause extreme pain.)
- Signs and symptoms associated with retinal detachment
- History of eye inflammation or systemic illnesses predisposing to uveitis
- History of trauma
- Use of IOP-lowering medications, including recent exposure to anesthesia
Physical
- Seidel positive wound leak
- Large bleb following trabeculectomy or tube shunt
- Inadvertent postoperative filtering bleb
- Hyperopic shift/reduced axial length
- Suspected traumatic globe rupture, especially if the following are present:
- 360° of subconjunctival hemorrhagic chemosis
- Peaked pupil
- Hyphema
- Intraocular foreign body
- Preexisting weakness in the globe integrity, such as staphyloma, coloboma, or an old incision
- Inflammatory cells and flare in the anterior chamber
- Shallowing of the anterior chamber
- Corneal edema and decompensation, especially in areas of corneal-iris touch
- Synechiae formation
- Corneal astigmatism
- Accelerated cataract formation
- Cyclodialysis cleft seen on gonioscopy
- Ciliochoroidal detachment - Serous or hemorrhagic
- Hypotony maculopathy
- Retinal folds
- Vascular engorgement and tortuosity
- Optic disc swelling
- Retinal detachment
- The anterior chamber is often deeper than usual when a retinal detachment is present.
- Vitreous hemorrhage or needle tract is visible on funduscopic examination.
Causes
- Unilateral hypotony
- Wound leak
- Overfiltering or inadvertent bleb
- Ciliary body detachment – Serous, hemorrhagic, or tractional
- Cyclodialysis cleft
- Inflammation - Iridocyclitis or blunt trauma
- Retinal detachment or retinotomy
- Ocular ischemia
- Scleral perforation with needle or suture, or scleral rupture following trauma
- Chemical cyclodestruction from antimetabolites
- Photocoagulation or cryoablation of the ciliary body
- Pharmacologic aqueous humor suppression
- Bilateral hypotony
- Systemic hypertonicity or acidosis - Dehydration, uremia, uncontrolled diabetes, or use of hyperosmotic agents
- Myotonic dystrophy
B-Scan Ocular Ultrasound
Choroidal Detachment
Endophthalmitis, Postoperative
Filtering Bleb Complications
Giant Cell Arteritis
Glaucoma, Drainage Devices
Glaucoma, Unilateral
Glaucoma, Uveitic
Hyphema
Laceration, Corneoscleral
Macular Edema, Irvine-Gass
Postoperative Flat Anterior Chamber
Retinal Detachment, Postoperative
Retinal Detachment, Rhegmatogenous
Retinal Detachment, Tractional
Uveitis, Evaluation and Treatment
Other Problems to be Considered
Suprachoroidal hemorrhage
Diabetic ketoacidosis
Uremia
Myotonic dystrophy
Dehydration
Lab Studies
- Hypotony is usually diagnosed based on only the history and the physical examination.
- In patients with undiagnosed but suspected uveitis, evaluate for systemic inflammatory disease, especially if the condition is recurrent.
- In patients with suspected temporal arteritis, measure C-reactive protein and erythrocyte sedimentation rate.
- In patients with bilateral hypotony, test for glucose, blood urea nitrogen, and creatinine.
Imaging Studies
Determining if the etiology is predominantly increased outflow or decreased inflow helps to establish treatment approaches.
- Ultrasonic biomicroscopy or anterior optical coherence tomography (OCT) can help to further evaluate the anterior chamber depth, the position of the ciliary body, and the presence of anterior ciliary detachment, cyclitic membrane, or cyclodialysis cleft. OCT of the posterior pole can help to better demonstrate subtle macular fluid or folds.
- Fluorescein angiography is useful in helping to distinguish retinal folds from choroidal folds.
- Intraoperatively, the ciliary body can be directly visualized to evaluate rotation and traction using endoscopy.
- B-scan ultrasonography is especially useful when the fundus is not easily visualized. It can help in determining the size and the extent of ciliochoroidal detachment, choroidal hemorrhage, and retinal detachment.
- Ultrasound studies of the carotid arteries are recommended for patients with suspected ocular ischemia.
Other Tests
- Wound leaks can be identified using the Seidel test.
- Concentrated fluorescein on a paper strip is preferable to topical fluorescein/anesthetic solution.
- The slit lamp is set to blue light, and the paper is stroked over the surface of the eye.
- Aqueous humor escape can be detected as spots of brighter yellow that slowly expand. Gentle pressure on the globe may be required to detect leaks.
- Wound leaks with overlying intact conjunctiva cause filtering blebs and remain Seidel negative.
Medical Care
- Hypotony is best managed by correcting the underlying problem. As a temporizing measure, the anterior chamber may be inflated with viscoelastic or a pars plana injection of viscoelastic or gas may be administered.
- No clinically useful medications are available that raise IOP as a primary action, although a recent study using topical ibopamine resulted in a significant reduction of hypotony.1
- Steroids may elevate IOP with prolonged use in individuals who are prone to a steroid response and may improve aqueous humor production by decreasing ciliary body inflammation.
- Increased fluid intake may slightly increase aqueous humor production.
- With inflammatory conditions or with recent surgery or trauma, topical prednisolone acetate is the mainstay of therapy. Additional therapy, such as topical or systemic nonsteroidal anti-inflammatory agents (NSAIDs), systemic, sub-Tenon, or intravitreal steroids, or other systemic medications (eg, methotrexate, cyclosporin), may be appropriate.
- Aqueous humor suppressants can decrease flow through an overfiltering bleb or a wound leak long enough for healing to occur but can potentially worsen hypotony. Use of acetazolamide to accelerate absorption of suprachoroidal fluid is controversial.
- Atropine and other cycloplegics deepen the anterior chamber to lessen iris-corneal touch.
- Pupillary dilation prevents a permanently small fixed pupil if synechiae form.
- Unfortunately, atropine also increases the uveoscleral outflow, although its benefits usually outweigh its risks.
Surgical Care
- Wound leaks
- Small wound leaks with a well-formed anterior chamber can be conservatively managed with patching or a large diameter bandage contact lens.
- Cyanoacrylate may be applied over a focal leak with a contact lens placed over the glue for comfort and stability.
- Larger wound leaks that cause clinically significant hypotony or seem unlikely to spontaneously resolve are best managed with surgical revision.
- Cyclodialysis cleft
- Separation of the ciliary body from the scleral spur creates a large direct channel for uveoscleral outflow. Detachment of the ciliary body may, but does not necessarily, reduce aqueous humor production.
- Cleft size does not bear directly on the degree of hypotony. The cleft may have been inadvertently created during ocular surgery or following trauma or intentionally created during a glaucoma operation.
- A cyclodialysis cleft may be identified gonioscopically, by anterior segment imaging, or during exploratory surgery. Gonioscopy can be difficult on a soft globe.
- Treatment options include argon laser photocoagulation, cryotherapy, external diathermy, and ciliary body suturing.
- When the cleft closes, a dramatic rise in IOP can occur.
- Clefts can spontaneously close.
- Miotics should be avoided to prevent recurrence of cleft opening. After cleft closure, long-term cycloplegia may be indicated.
- Retinal detachment
- Rhegmatogenous retinal detachment is usually associated with mild hypotony. Occasionally, with large detachments, profound hypotony may develop.
- The mechanism is believed to be the egress of aqueous humor through the vitreous, the retinal hole, and across the RPE. Concurrent iridocyclitis may also reduce aqueous humor production.
- Hypotony may slowly resolve following repair of the detachment because of lingering inflammation, or it may quickly reverse if, for example, a scleral buckle or silicone oil is used.
- Overfiltering bleb or tube shunt, or posttraumatic hypotony
- Acute
- Mild transient hypotony following glaucoma surgery is common and usually well tolerated.
- Observe and treat with liberal anti-inflammatory agents, cycloplegic agents, and reformation of the anterior chamber with viscoelastic, if needed. Viscoelastic injections may be repeatedly given.
- Continue topical antibiotics for several days beyond the last chamber reformation procedure.
- Anterior chamber shallowing becomes clinically significant if corneal-iris touch or corneal-lens touch results in corneal decompensation or synechiae develop.
- Consider draining large choroidal effusions if no sign of resolution is present after several days, especially if retinal apposition exists, the anterior chamber is markedly shallow, or the patient is at higher risk for hemorrhage. Hemorrhage risk factors include advanced age, history of glaucoma, history of vascular disease, and anticoagulated status.
- Chronic
- Surgical wound revision with resuturing of the scleral flap and/or conjunctival advancement or autograft is the procedure of choice for incompetent trabeculectomy. Blood patch, laser application, cautery, cryotherapy, and trichloracetic acid may work in some instances but are less effective.
- Conjunctival flaps alone can work well for diffusely incompetent blebs due to tissue thinning and avascularity.
- Focal leaks may be treated with cyanoacrylate and a bandage lens.
- Eroded tube shunts can be particularly challenging to stabilize, and a number of graft alternatives, including cornea, dermis, and fascia lata, have been used with success. Care must be taken to remove any epithelial tissue that has grown in through the erosion.
- Uveitis
- Anti-inflammatory agents are the mainstay of treatment. Intravitreal steroid injections have been used with some success, even in prephthisical eyes. Surgical removal of a cyclitic membrane may release tractional detachment of the ciliary body.
- Vitrectomy and placement of silicone oil may be useful in refractory cases.
Consultations
- Practitioners who have limited experience with hypotony should consider consultation with a glaucoma or retina subspecialist.
- Rheumatologic or internal medicine consultation is appropriate for difficult uveitic cases and for patients with uncontrolled systemic disorders.
Diet
Patients at risk for hypotony should maintain good hydration.
Activity
- The patient should avoid lifting, bending, and strenuous activity. Sudden movement or straining could cause a vessel, which is already stretched in the suprachoroidal space, to bleed and create a suprachoroidal hemorrhage.
- The patient should avoid any direct pressure on the eye that could cause further decompression. An eye shield, especially during sleep, is advisable.
Topical anti-inflammatory agents, especially prednisolone acetate 1%, are indicated in all types of hypotony. NSAIDs may be used adjunctively. Cycloplegic agents are often indicated in swollen eyes. Topical broad-spectrum antibiotics are appropriate with wound leaks and in recent surgery or trauma cases.
Drug Category: Corticosteroids
Have anti-inflammatory properties and cause profound and varied metabolic effects. Corticosteroids modify the body's immune response to diverse stimuli.
| Drug Name | Prednisolone acetate 1% (Pred Forte) |
|---|
| Description | A glucocorticoid that inhibits edema, fibrin deposition, capillary dilation, and phagocytic response of acute inflammation. Also inhibits capillary proliferation, collagen deposition, and scar formation. Corneal penetration is good. |
|---|
| Adult Dose | 1-2 gtt in the conjunctival sac bid/qid |
|---|
| Pediatric Dose | Administer as in adults |
|---|
| Contraindications | Documented hypersensitivity; viral, fungal, or tubercular infections |
|---|
| Interactions | Effects may decrease in patients taking phenytoin, barbiturates, and rifampin |
|---|
| Pregnancy | C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
|
|---|
| Precautions | Caution in hypertension; known to cause cataract formation with long-term use; suspect fungal invasion in any persistent corneal ulceration where a corticosteroid has been used or is in use (obtain fungal cultures when appropriate) |
|---|
Drug Category: Mydriatics/Cycloplegics
Relax any ciliary muscle spasm that can cause a deep aching pain and photophobia.
| Drug Name | Atropine sulfate 0.125%, 0.25%, 0.5%, or 1% (Isopto, Atropair) |
|---|
| Description | Potent and long-acting agent that produces paralysis of accommodation (cycloplegia) and pupillary dilation (mydriasis). In uveitis, cycloplegics relax the intraocular muscles, decreasing pain and photophobia. Reduce abnormal vascular permeability, and dilate the pupil. |
|---|
| Adult Dose | Solution 0.5-1.0%: 1 gtt qd/qid
Ointment: Apply 0.5-inch ribbon in conjunctival sac tid |
|---|
| Pediatric Dose | Solution 0.125%, 0.25%, 0.5%: 1 gtt qd/tid |
|---|
| Contraindications | Documented hypersensitivity; thyrotoxicosis; narrow-angle glaucoma; tachycardia |
|---|
| Interactions | Coadministration with other anticholinergics have additive effects; pharmacologic effects of atenolol and digoxin may increase with atropine; antipsychotic effects of phenothiazines may decrease with this medication; tricyclic antidepressants with anticholinergic activity may increase effects of atropine |
|---|
| Pregnancy | C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
|
|---|
| Precautions | Avoid in Down syndrome and/or children with brain damage to prevent hyperreactive response; avoid in coronary heart disease, tachycardia, congestive heart failure, cardiac arrhythmias, and hypertension; caution in peritonitis, ulcerative colitis, hepatic disease, and hiatal hernia with reflux esophagitis; in prostatic hypertrophy, prostatism can have dysuria and may require catheterization |
|---|
Drug Category: Nonsteroidal anti-inflammatory agents
Have analgesic and anti-inflammatory actions. Their mechanism of action is not known but may inhibit cyclooxygenase activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell membrane functions.
| Drug Name | Diclofenac 0.1% (Voltaren) |
|---|
| Description | Inhibits prostaglandin synthesis by decreasing activity of enzyme cyclooxygenase, which, in turn, decreases formation of prostaglandin precursors. May facilitate outflow of aqueous humor and decrease vascular permeability. |
|---|
| Adult Dose | 1 gtt in conjunctival sac up to qid |
|---|
| Pediatric Dose | Not established |
|---|
| Contraindications | Documented hypersensitivity; avoid during pregnancy |
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| Interactions | Additive effect with systemic NSAIDs may occur |
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| Pregnancy | B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
|
|---|
| Precautions | Corneal thinning may occur |
|---|
| Drug Name | Ketorolac 0.5% (Acular) |
|---|
| Description | Inhibits prostaglandin synthesis by decreasing activity of the enzyme, cyclooxygenase, which results in decreased formation of prostaglandin precursors, which, in turn, results in reduced inflammation. |
|---|
| Adult Dose | 1 gtt in conjunctival sac up to qid |
|---|
| Pediatric Dose | Not established |
|---|
| Contraindications | Documented hypersensitivity |
|---|
| Interactions | None reported |
|---|
| Pregnancy | B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
|
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| Precautions | Perform ophthalmologic studies in patients who develop eye complaints during therapy; discontinue therapy if changes are noted; changes may include blurred or diminished vision, corneal deposits, retinal disturbances, scotomata, changes in color vision, and macula degeneration |
|---|
Further Outpatient Care
- Patients should receive vigilant follow-up care until the hypotony and the underlying cause have been stabilized.
Deterrence/Prevention
- Hypotony following glaucoma surgery can be prevented in several ways.
- Consider lowering the exposure time and the concentration of antimetabolites, if used.
- Using releasable sutures or placing extra sutures (which can be removed with laser suture lysis) in the trabeculectomy flap may prevent overfiltration.
- For tube shunts, choosing a valved device or modifying the shunt with suture material can slow drainage.
- Many glaucoma surgeons leave the anterior chamber inflated with viscoelastic at the end of each case.
- Aggressive use of anti-inflammatory agents can help prevent the cycle of iridocyclitis and hypotony.
Complications
- Corneal decompensation, synechiae, cataract formation, and chronic retinal edema or folds may occur. Hypotony maculopathy can cause permanent RPE disruption.
- If suprachoroidal hemorrhage develops, the results are often catastrophic for the eye.
- Prolonged hypotony may lead to prephthisis or phthisis bulbi.
Prognosis
- Prognosis varies with the cause and the extent of hypotony.
Patient Education
- Educate patients about the cause and the implications of this condition. Better understanding may help the patient to be more compliant with treatment and follow-up care. Patients should also be warned of the potential chronicity of hypotony. Improvement in visual acuity often lags behind the resolution of hypotony.
- Emphasize activity limitations, use of eye shield, compliance with medications, and increased fluid intake.
- Encourage patients to contact the office if their situation seems to be worsening.
Medical/Legal Pitfalls
- Patients undergoing glaucoma surgery should be advised that they may experience at least mild hypotony following their operation. Communicating the risk and implications of hypotony should be part of the preoperative teaching and consent process.
| Media file 1:
Seidel positive wound leak around a conjunctival suture. |
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| Media file 2:
Conjunctival advancement flap sewn over a diffusely incompetent bleb. |
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Media type: Photo
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| Media file 3:
Eroded tube shunt in a patient with rheumatoid arthritis. |
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Media type: Photo
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| Media file 4:
Flat anterior chamber with iris-corneal touch following a phacotrabeculectomy. |
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Media type: Photo
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| Media file 5:
Autologous blood injected into an overfiltering bleb to create a blood patch. |
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Media type: Photo
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| Media file 6:
B-scan ultrasound of choroidal effusions before and after surgical drainage. |
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Media type: Ultrasound
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Ocular Hypotony excerpt Article Last Updated: Nov 12, 2007
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