Ocular hypotension during short-and long-term hypocapnia

Alon Harris, Victor Malinovsky, Bruce J. Martin

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Severe, short-term decreases in alveolar Pco<inf>2</inf> acutely lower intraocular pressure (IOP). We wondered if less severe, physiologically relevant Pco<inf>2</inf> reductions would also lower ocular tension and if this effect would persist in the longer term. To investigate the acute influence of small Pco<inf>2</inf> changes on IOP, 11 healthy persons hyperventilated to reduce end-tidal Pco<inf>2</inf> by first 10% (5 min) and then 20% (5 min). IOP fell when Pco<inf>2</inf> fell 20% (14.5 ± 2.1 mm Hg vs. 16.8 ± 1.0 in a matched control series; p < 0.05) and remained depressed 20 min after Pco<inf>2</inf> had returned to baseline levels. To investigate the persistence over time of this hypocapnia-associated IOP reduction, nine healthy persons hyperventilated to reduce end-tidal Pco<inf>2</inf> by 15% for 1 h. IOP was substantially reduced by 30 min (11.7 ± 0.5 vs. 14.8 ± 0.6 mm Hg; p < 0.05) and at 60 min (11.2 ± 0.7 vs. 14.2 ± 0.6 mm Hg; p < 0.05) of sustained hypocapnia. In contrast, when the effects of acute hypocapnia were compared with standard nonselective (3-adrenergic blockade (levobunolol HC1, 1 drop0.5% solution instilled 12 and 2 h before study; N = 1 normals), a 20% Pco<inf>2</inf> reduction was less effective in lowering IOP than was drug treatment, and induction of hypocapnia failed to alter IOP after drug treatment [baseline IOP 14.4 ± 1.3 mm Hg vs. 10.0 ± 1.6 mm Hg after levobunolol (p < 0.05) and 10.7 ±1.9 mm Hg after hypocapnia and levobunolol were combined]. In addition, 3 days’ treatment with the ventilatory stimulant drug medroxyprogesterone acetate (150 mg/day in 10 men, initial IOP s= 18 mm Hg) significantly elevated ventilation and lowered Pco<inf>2</inf> but failed to change IOP. We conclude that although IOP is clearly linked to Pco<inf>2</inf> in the short term, manipulation of Pco<inf>2</inf>, either alone or in combination with drug therapy, may not be an effective means for long-term IOP reduction.

Original languageEnglish (US)
Pages (from-to)226-231
Number of pages6
JournalJournal of glaucoma
Issue number3
StatePublished - Jan 1 1994


  • Carbon dioxide
  • Hyperventilation
  • Intraocular pressure
  • Isocapnia
  • Medroxyprogesterone acetate
  • P-adrenergic blockade

ASJC Scopus subject areas

  • Ophthalmology

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    Harris, A., Malinovsky, V., & Martin, B. J. (1994). Ocular hypotension during short-and long-term hypocapnia. Journal of glaucoma, 3(3), 226-231.