WHICH ANGLE OF HEAD-DOWN TILT BETTER SIMULATES THE INCREASE IN INTRA-OCULAR PRESSURE THAT OCCURS IN MICROGRAVITY?

Luís Francisco B. Chotgues, MD Dario F. G. de Azevedo, Ph.D.

Thais Russomano, MD, Ph.D.

Physiology of the eye on Earth

• Aqueous Humor

Microgravity Laboratory-PUCRS

Intra-ocular pressure (IOP) in microgravity AUTOMATIC SELF-TONOMETRY 1st German-Russian MIR mission 1992 : 92% IOP rise

Schwartz R, Draeger J, Groenhoff S, Flade K D

Ophthalmologe 1993 Dec; 90(6): 640-2 2nd German D-2 Spacelab-Mission 1993: 114% IOP rise

Draeger J, Schwartz R, Groenhoff S, Stern C

Ophthalmologe 1994 Oct; 91(5): 697-9

Microgravity Laboratory-PUCRS

IOP during parabolic flight IOP increased 58% (19 mmHg) during parabolic flight (20 s of µG) compared to baseline values (12 mmHg) ( n =11) Mader TH et al., Am J Ophtalmol. 1993 Mar 15; 115(3):347-50

Microgravity Laboratory-PUCRS

IOP during HDT Objectives

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To determine the angle of head-down tilt that best simulates the increase in IOP after 15 min insertion in microgravity To evaluate the mechanisms involved in the increase in the IOP during microgravity and HDT To contribute to the diagnosis and treatment of patients who suffer from glaucoma

Microgravity Laboratory -PUCRS

IOP during HDT Protocol

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Number of subjects: 8 (16 eyes) Portable aplanation tonometer IOP measurements:

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Sitting position (after 5 min - baseline) 4 randomized angles of HDT (after 15 min):

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6, 12, 18 and 34 degrees

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Time of day: 8 - 12 AM Test duration per subject: 2 h

Microgravity Laboratory-PUCRS

IOP during HDT Material and Methods

Microgravity Laboratory-PUCRS

IOP during HDT Material and Methods

Microgravity Laboratory-PUCRS

Results Intra-ocular Pressure (mmHg) Body position Sitting 6

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HDT 12

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HDT 18

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HDT 34

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HDT

Microgravity Laboratory-PUCRS

Mean +/- SE 12.6 +/- 0.5

17.0 +/- 0.7

18.9 +/- 0.7

19.6 +/- 0.7

27.0 +/- 1.5

p < or = 0.05

S S S S

IOP during HDT Results 120 100 80 60 40 20 0 31 55 63 6° HDT

Microgravity Laboratory-PUCRS

12° HDT 18° HDT Body Position 110 34° HDT

IOP during HDT and Microgravity 120 100 80 60 40 20 0 31 55 63 110 114 92 6° HDT 12° HDT 18° HDT 34° HDT D2 mission* Ger-Russ Mir** Body Position

Microgravity Laboratory-PUCRS

* Draeger J et al., 1993 ** Schwartz R et al., 1992

IOP during HDT Conclusion

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IOP enhanced 110% after 15 min of 34° of HDT 34° of HDT was accepted as the angle that best simulates the acute increase in IOP that occurs in microgravity 6° of HDT did not produce the rise in IOP that has been found during space missions

Microgravity Laboratory-PUCRS

IOP during HDT Future Studies

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Increase in IOP in microgravity versus during HDT - Mechanism?

Measurement of venous pressure and IOP during HDT Increase in IOP = Glaucoma

Microgravity Laboratory-PUCRS

Central venous pressure in space Buckey J. C. et al, 1996

Microgravity Laboratory-PUCRS

Venous pressure in the forehead during HDT

Microgravity Laboratory-PUCRS