What should be done if a tonometer indicates elevated intraocular pressure in a patient with cystic fibrosis (Cystic Fibrosis, CF) in an emergency setting?

Emergency Management of Elevated Intraocular Pressure in Cystic Fibrosis Patients

If tonometry indicates elevated IOP in a CF patient in an emergency setting, immediately perform gonioscopy to differentiate angle-closure from open-angle mechanisms, then initiate IOP-lowering therapy with topical medications while arranging urgent ophthalmology consultation, as CF patients may have baseline ocular abnormalities that complicate interpretation. 1

Immediate Assessment Algorithm

Step 1: Verify the IOP Measurement Accuracy

• Recognize that standard Goldmann applanation tonometry may be unreliable in CF patients who may have corneal abnormalities, including decreased tear film break-up time (present in 44% of CF patients) and potential corneal surface changes 2, 3
• If corneal edema or surface irregularity is present, use alternative tonometry methods such as pneumotonometer, rebound tonometry (iCare), or dynamic contour tonometer rather than relying solely on Goldmann readings 1, 4
• The pneumotonometer generates 40 readings per second and conforms to irregular corneal surfaces, making it preferable when corneal abnormalities are suspected 1, 4

Step 2: Perform Emergency Gonioscopy

• Gonioscopy is mandatory to determine if elevated IOP is due to angle-closure (requiring immediate intervention) versus open-angle mechanisms 1
• Perform compression gonioscopy with a four-mirror lens in a dark room using a bright, short beam that does not pass through the pupil to avoid inducing pupillary constriction 1
• Wait 10 seconds after lens placement to allow the pupil to resume its resting state, which may demonstrate pupillary block configuration 1
• If corneal edema impairs visualization, apply topical glycerin to clear the cornea 1

Step 3: Differentiate Acute Angle-Closure from Open-Angle Elevation

For Acute Angle-Closure Crisis (AACC):

• Look for conjunctival hyperemia, corneal edema (microcystic and stromal), mid-dilated or irregular pupil, and shallow anterior chamber 1
• Initiate immediate medical therapy with topical IOP-lowering agents and arrange for urgent laser peripheral iridotomy 1
• Avoid dilating the pupil, as this can precipitate or worsen angle-closure 1

For Open-Angle IOP Elevation:

• Measure IOP in both eyes using Goldmann applanation tonometry as the standard method 1
• Document baseline IOP, as elevated IOP is a major risk factor for glaucomatous progression 1
• Note that CF patients may have retinal nerve fiber layer thinning (particularly in the nasal-inferior quadrant), which could indicate pre-existing vulnerability to IOP-related damage 2, 5

CF-Specific Considerations

Ocular Manifestations in CF That Affect Emergency Management

• CF patients have significantly decreased inferior-quadrant peripapillary retinal nerve fiber layer thickness compared to controls, suggesting baseline vulnerability to optic nerve damage from elevated IOP 2
• Tear film abnormalities are common (56% of CF patients have abnormal tear break-up time), which may affect tonometry accuracy and require alternative measurement methods 2
• Visual field defects correlate with pulmonary function parameters (FEV1%, FVC%) and oxygen saturation, indicating that hypoxia may affect retinal ganglion cells 5

Systemic Factors Influencing Emergency Care

• Assess respiratory status including oxygen saturation, as CF patients with severe pulmonary disease may have compromised oxygenation affecting retinal function 5, 6
• CF patients may be on multiple medications and have complex medical histories requiring coordination with pulmonology 6
• Screen for pulmonary hypertension with transcutaneous oxygen saturation in the upright position, as portosystemic shunting complications can occur 1

Pharmacologic Management

Initial Medical Therapy for Elevated IOP

• For angle-closure crisis: Administer topical beta-blockers, alpha-agonists, and carbonic anhydrase inhibitors immediately 1
• For open-angle elevation: Initiate topical IOP-lowering therapy based on the degree of elevation and risk factors 1
• Consider intravenous acetazolamide 250-500 mg for rapid IOP reduction in acute cases, with subsequent dosing of 250 mg every 4 hours as needed 7
• The preferred acetazolamide dosage for acute glaucoma is 250 mg every 4 hours, though some acute cases may require an initial 500 mg dose followed by 125-250 mg every 4 hours 7

Critical Medication Considerations

• Avoid medications with anticholinergic or adrenergic effects (including ipratropium bromide and salbutamol-containing inhalers commonly used in CF) as these can precipitate angle-closure 1
• Acetazolamide interferes with theophylline assays and may produce increased urinary crystals, which is relevant given CF patients' complex medication regimens 7

Common Pitfalls and How to Avoid Them

Pitfall 1: Relying Solely on Goldmann Tonometry

• CF patients have ocular surface abnormalities that may render Goldmann readings inaccurate 2, 3
• Always consider alternative tonometry methods when corneal abnormalities are present 1, 4

Pitfall 2: Missing Angle-Closure Component

• Never assume open-angle mechanism without performing gonioscopy, as angle-closure requires fundamentally different emergency management 1
• Gonioscopy must be performed on both eyes, as the fellow eye is at risk 1

Pitfall 3: Inappropriate Pupil Dilation

• Dilation is contraindicated until angle-closure is ruled out by gonioscopy 1
• If fundus examination is essential before gonioscopy, attempt visualization using direct ophthalmoscopy, slit-lamp biomicroscopy with indirect lens, or non-mydriatic fundus photography 1

Pitfall 4: Underestimating Baseline Optic Nerve Vulnerability

• CF patients may have pre-existing retinal nerve fiber layer thinning and visual field defects related to chronic hypoxia 2, 5
• Set lower target IOP thresholds in CF patients with evidence of optic nerve compromise 1

Disposition and Follow-Up

Urgent Ophthalmology Consultation

• Arrange immediate ophthalmology consultation for any CF patient with IOP >21 mmHg or signs of angle-closure 1
• Document visual acuity, pupil examination, slit-lamp findings, IOP measurements, and gonioscopy results for the consulting ophthalmologist 1

Ongoing Monitoring Requirements

• CF patients require regular ophthalmologic assessment given their baseline ocular abnormalities and potential for progressive changes 2
• IOP should be measured at follow-up visits using consistent methodology, with gonioscopy performed periodically or when unexplained IOP changes occur 1