Article Text

Download PDFPDF

Bilateral choroidal effusions after taking acetazolamide for altitude sickness
  1. Alice Rothwell and
  2. Owen Anderson
  1. Ophthalmology, University Hospitals Dorset NHS Foundation Trust, Bournemouth, UK
  1. Correspondence to Dr Alice Rothwell; alicerothwell{at}


A fit and healthy 44-year-old woman took a single dose of oral acetazolamide (125 mg) in preparation for a hiking trip to Everest base camp. She awoke the next morning with profoundly blurred distance vision. She presented to eye casualty later that morning, approximately 18 hours postingestion: examination demonstrated myopia and bilateral choroidal effusions. Acetazolamide is used to minimise symptoms of altitude sickness. Rarely, its use can be linked with ophthalmic side effects, such as myopia. A handful of case reports also describe choroidal effusions secondary to its use as part of ophthalmic treatment (eg, postoperatively). This is the first reported case in which choroidal effusions have been demonstrated as a side effect of its prophylactic use against altitude sickness.

  • retina
  • mountain sickness

Statistics from

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.


Acetazolamide may be used for the prophylaxis of altitude sickness. Typically, a daily dose of 250 mg is considered efficacious in preventing acute mountain sickness.1 Frequently, this is divided into two 125 mg doses taken every 12 hours, started 24 hours prior to ascending in elevation, and discontinued 48 hours after reaching highest elevation.2 More than 100 million people per year travel to altitudes of greater than 2500 m above sea level, where hypoxic conditions induce altitude sickness in 10%–20% of unacclimatised individuals.

At such altitudes, reduced oxygen tension can lead to hypoxia; the body responds with compensatory hyperventilation, which in turn may cause respiratory alkalosis. Respiratory alkalosis plays a central part in altitude sickness.

Oral acetazolamide may be taken to manage such symptoms. It inhibits carbonic anhydrase in the renal proximal tubule, increasing bicarbonate excretion. The resultant metabolic acidosis offsets the original respiratory alkalosis.

An additional effect of acetazolamide is the lowering of intraocular pressures (IOP), due to the inhibition of carbonic anhydrase found within the eye’s cilliary body epithelium. There is reduced formation of bicarbonate, thereby decreasing fluid transport, and lowering IOP. For this reason, oral acetazolamide is occasionally used in ophthalmic practice to control IOP postoperatively.

In rare cases, acetazolamide has been shown to induce myopia and choroidal effusions when given postoperatively in certain ophthalmic procedures. Myopia has been reported when used in the prevention or treatment of altitude sickness. Most people taking acetazolamide for altitude sickness are located in remote mountainous regions, with an obvious lack of access to specialist ophthalmic services.

We present a case report in which a British adult woman used oral acetazolamide to prevent potential altitude sickness. This is the first reported case in which choroidal effusions have been demonstrated as a side effect of this drug’s prophylactic use against altitude sickness. Significant myopia occurred after a single dose of 125 mg. Her case highlights the importance of assessing potential pharmacological side effects before embarking on travel. Significantly blurred vision can be potentially life-threatening at high altitude, due to the physical and visual demands of the environment.

Case presentation

A 44-year-old woman presented to eye casualty at 11:00 having woken up at 08:00 with acutely blurred vision in both eyes. She was otherwise fit and well. She took no regular medications. However, she had taken 125 mg of oral acetazolamide 18 hours previously, at 17:00 the day before. She was planning to use acetazolamide to prevent altitude sickness on her forthcoming trip to Nepal.

There was no significant ophthalmic or medical history. She was a radiographer, drove, and did not smoke.


Visual acuities were recorded using a Snellen chart: 18 hours postacetazolamide ingestion, her bilateral visual acuity was reduced to counting fingers, improving to 6/12 with pinhole. The following day, 40 hours postacetazolamide ingestion, visual acuity was 6/150 bilaterally. However, 6/7.6 was achieved in the right eye with the addition of a −5.50 defocus smoothing (DS) lens; in the left eye, visual acuity improved to 6/6 with a −5.0 DS lens. She reported her unaided acuity, before taking acetazolamide, as ‘excellent’. She had never worn glasses.

Her pupils were equal and reactive to light, with no relative afferent pupillary defect. Colour vision was full. IOPs were 12 mm Hg bilaterally (within normal range). Assessment of her cranial nerves was unremarkable, and confrontational visual fields were full.

Anterior segment examination demonstrated clear corneas, with scanty cells (<0.5+) in the anterior chambers (ACs). Both ACs were shallow (figure 1), and gonioscopy demonstrated angle iris-trabecular meshwork contact throughout 180° of each eye. Fundal examination demonstrated no indication of vitritis or retinitis; both optic discs and maculae were healthy.

Figure 1

Optical coherence tomography (OCT) scan of the front part of the left eye. The iris (*) and lens (#) are seen inferiorly, with the cornea arching over the top. (A) An OCT scan 2 days following taking acetazolamide while (B) The same scan 2 months later, when vision had returned to normal. Arrows show the drainage angle, which, in (A), is initially very narrow due to the anterior displacement of the lens caused by the underlying choroidal effusion. With time, the angle opens up (B) as the choroidal effusion resolves, the lens moves backwards to its normal position and the anterior chamber deepens.

Both superior retinas were diffusely elevated, and the ora serrata (retinal edge) was visible in the left eye. This is not normally visible, and suggested a choroidal detachment (figure 2). IOL master measurements were made of both eyes. Axial lengths (cornea to retina) were 22.91 mm (right eye) and 22.77 mm (left eye). AC depths were 2.50 mm (right eye) and 2.45 mm (left eye).

Figure 2

Ultrasound scan of superior retina of left eye. The arrow indicated the choroidal detachment. This choroidal detachment was also visible clinically.

Optical coherence tomography (OCT) scanning of the front of the eye showed shallow ACs and angle closure. Macular OCT scanning showed choroidal thickening and mild undulation of the retinal–choroidal interface. Ultrasound scans showed bilateral anterior choroidal effusions superiorly. All tests were performed at 40 hours postacetazolamide ingestion.

Initial investigations, including inflammatory blood markers, and an MRI of her head and orbits, were unremarkable.


The patient was advised to stop taking acetazolamide; steroid eye drops (dexamethasone 0.1%, four times a day) were started.

Outcome and follow-up

Two days later, her unaided visual acuity had improved to 6/60 bilaterally; this improved to 6/6 with a −2.5 and −3.5 DS lens in the right and left eye, respectively. Her ACs had deepened to 2.96 mm (right) and 2.86 mm (left). IOPs were 18 mm Hg bilaterally. Gonioscopy demonstrated open drainage angles. The choroidal effusions had improved. Given this improvement, she was advised that she could fly to Nepal, where she was due to begin hiking 4 days later.

After returning from Nepal, she was assessed again. Her unaided visual acuity had improved to 6/5 (right) and 6/6 (left); AC depths had increased further to 3.32 mm (right) and 3.30 mm (left). The choroidal effusions had completely resolved.

OCT scans supported these findings: both ACs were deep, with open drainage angles; the macular scans showed complete resolution of the macular choroidal thickening and undulation of the retinal–choroidal interface.

She reported that her vision returned to normal 7 days after taking the acetazolamide, and 1 day before starting hiking to Everest base camp.


Acetazolamide is commonly used to prevent and treat symptoms of altitude sickness. Doses of 125 mg two times per day are effective in prevention, occasionally increased to 250 mg two times per day if symptoms are present. Regarding prophylaxis, 125 mg two times per day has been shown to be as effective as higher doses, but with fewer side effects.3

While its use for altitude sickness is known to occasionally cause myopia,4 there are no reported cases of choroidal effusions with acetazolamide used in altitude sickness. This is understandable, as patients are usually in isolated rural locations when taking this drug to prevent altitude sickness. Therefore, there is difficulty in accessing ophthalmic specialist services.

Acetazolamide has been reported to cause choroidal effusions and myopia when used to treat patients undergoing ophthalmic procedures. The reported doses ranged from 250 to 500 mg.5 6 Our patient developed choroidal effusions after just 125 mg. There have been no previous reported cases of choroidal effusions occurring after such a low single dose.

The timings symptom-onset, choroidal detachment and symptom-resolution were similar to reported cases in which acetazolamide has been used prophylactically in ocular surgery. Symptoms are usually present the next day, as in our case, and fully resolve by 5–14 days.7 8 Our case had resolution of symptoms at 7 days.

A cycloplegic, such as atropine, not used in this patient’s management. This was because the IOPs were not raised. Two days later, the anterior chamber had deepened spontaneously, and the IOPs remained normal.

AC shallowing, with forward movement of the lens, is the reason for the induced myopia. Forward movement of the lens, due to the underlying choroidal effusion, causes the eye to focus light in front of the retina, as opposed to on it. This myopia (short sightedness) resolves once the lens moves back to its original position. Figure 1 shows shallowing of the eye’s AC with narrowing of the drainage angle. An additional finding was increased choroidal thickness in the macular region. This was associated with undulation of the retinal–choroidal interface. This has been noted on OCT scanning before,9 and resolves with cessation of acetazolamide.

Notably, our patient developed profound myopia after only a single, small acetazolamide dose. Her visual acuity dropped from 6/6 to 6/150. She was sensible enough to test the drug at home before she left for Nepal. This allowed any side effects to be identified when in a safe environment. Had she been hiking when her vision dropped, she could have come to harm due to her poor vision. In mountainous environments, with rocky and unstable terrain, the risk of personal injury through trips and falls is potentially fatal. Blurred vision might be an inconvenience when in a familiar, low-altitude environment; but at high altitude, in the cold, and without access to medical resources, any visual impairment could conceivably become life-threatening.10

When considering prescribing acetazolamide for altitude sickness prophylaxis, we recommend the following guidance: patient to start the medication when in a safe environment, to allow for an assessment of possible side effects. While the absence of side effects on starting the drug does not fully exclude side effects later, it does go some way to reduce this risk.11 Several systemic side effects secondary to acetazolamide have been widely documented: paraesthesia, fatigue and polyuria.12 Induced myopia can cause significant visual problems, which may last for several days and potentially jeopardise personal safety. If intolerable side effects are pre-emptively identified, the patient might then safely choose to stop taking the acetazolamide and seek alternative medication, such as oral dexamethasone (8 mg initially, followed by 4 mg every 6 hours).13 If intolerable altitude sickness were to occur, despite prophylactic medication, the best mode of treatment is to descend from altitude.

Patient’s perspective

I was due to be going on a trekking holiday, and was advised to take Diamox to help combat possible altitude sickness, sampling and to sample it beforehand to see if I would have any side effects. This turned out to be really valuable advice. I took half of the prescribed daily dose on Sunday evening, but it was Monday morning I woke to find my eyesight had changed dramatically!

Long distance everything had become a blur, I could make out objects due to the familiarity and recognition, but could not distinguish depth or height which made walking very unsteady. Everything had a black outline edge, people looked like they had very heavy black eyeliner with no definition to their faces. Close sight had become so short that I could only read something by bringing the wording so close that with normal sight, eyes would feel they would go ‘cross-eyed’. Bright lights and car headlights looked like ‘exploding fireworks’. It was very scary; just moving around was hazardous, I could not do daily tasks let alone drive or go to work.

Initially I did not associate it with having been a cause of taking the diamox, I was more concerned that I'd had suddenly had an unexplained stroke or cerebrovascular accident. It certainly had the Ophthalmology team puzzled and MRI scans were normal. And then when I remembered about the diamox, allergic reaction seemed to be the only explanation, though this was totally extreme occurrence.

It was alarming that it took about 3 days before I started to notice any change in my eyesight as it slowly returned back to normal, and was a full 7 days before fully restored. I was constantly testing and checking. At first when there was no change I was panicked thinking this was it, my life was changed for ever and I had totally lost my independence. The relief when I woke on the fourth morning to find there was marked improvement, was immense.

Learning points

  • Although very unusual, acute myopia and choroidal effusions can occur after oral administration of acetazolamide.

  • This can occur after doses as low as a single 125 mg dose.

  • Vision can become profoundly blurred—this is particularly dangerous if occurring for the first time at high altitude, where trips and falls could be fatal, and the patient has limited medical access.

  • If taking acetazolamide to prevent altitude sickness, we advise a drug ‘trial’ while in a safe environment, to allow any potential side effects to be identified and managed.

  • Adventurous patients and their practitioners should keep their eyes peeled for this potentially serious and sight-threatening side effect.

Ethics statements

Patient consent for publication



  • Contributors AR is the primary author and contributor of this case report. She conceived the idea, planned the report, collected information from clinical documentation pertaining to this case, and wrote the case report, which was then submitted to OA for his review. OA is an ophthalmology consultant who assessed and managed the patient when she presented to the Eye Unit with visual blurring. He has reviewed and edited the case report after it was written by AR.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.