Intraocular pressure

[David Glasser]

Hi all -

I'm an ophthalmologist who has been asked about eye pressure at depth. It's been too many years for me to rely on my recall of the details from college physics, so I thought I would post here and ask the experts.

At sea level the normal intraocular pressure (IOP) ranges from about 10-20 mm Hg, let's say 15 mm Hg, higher than ambient atmospheric pressure. At depth, I assume that the pressure inside the eye does not increase, since, like the rest of the body structures that contain no gas, the eye is not compressible. Do I have this right so far?

If the above is correct, for someone who has had eye surgery, where a full-thickness incision into the eye has healed but never gains the full strength of the unoperated eye wall, I would also assume that there is no risk of incision rupture due to pressure changes.

However, as a diver descends, doesn't the air in the mask compress, leading to an increase in the differential between the pressure inside the eye and the air pressure inside the mask? I understand that divers equalize this pressure by adding air to the mask as they descend. Has anyone ever looked at how close to "normal" this equalization is? Could it be off by 10, 20, 30 mm Hg or more?

If the pressure differential between the inside of the mask and the eye is high enough, I imagine it might risk rupturing an incision. Or even in divers with no history of eye surgery, could it cause gradual damage to the pressure-sensitive optic nerve, as in glaucoma, if the differential is maintained for hours at a time? Do professional divers stay down that long? I am not aware of any increased risk of glaucoma-like damage in divers, at least in the medical literature, but I only found one reference with a PubMed search (below). It didn't address this directly, and raised yet another question: why would angles narrow further, risking precipitation of an acute narrow angle glaucoma attack, during ascent?

Appreciate it if any of you are able to educate me further.

Thanks,
David Glasser

Klin Monatsbl Augenheilkd. 1976 Feb;168(02):253-7.
[Intraocular pressure in snorkling and diving (author's transl)][Article in German]
Kalthoff H, John S.
The reactions of the intraocular pressure (i.o.p) in snorkling and scuba diving were studies on 29 healthy subjects. A patient with chronic glaucoma simplex was examined in a pressure tank. The results confirm the author's opinion, that a well compensated chronic glaucoma simplex with intact discs and fields does not exclude fitness to dive. However, a diver with narrow angel glaucoma risks sudden rise in i.o.p. and acute glaucoma while ascending to the surface. Persons, who are examined for fitness to dive, should be seen by an ophthalmologist, if they have a glaucoma or if they are hypermetropic and over 40 years of age.
PMID: 957553 [PubMed - indexed for MEDLINE]

 

[TSandM]

I don't think anybody but the most novice diver dives for even several minutes at a time with a mask that's far off ambient pressure. It's too uncomfortable. There is, however, a very small gradient, judging from the fact that my strap frequently gets pushed up over the top of my head without my mask falling off . . . Exactly what that pressure difference is, I don't know. It's not enough to leave a mark on my face after a dive.

I can't think of any reason why a person with narrow-angle glaucoma would suffer an attack on ascent. However, diving at depth in poor visibility is a situation of markedly reduced ambient light, which would cause pupillary dilation. I don't know if it would be enough to bring on an attack of narrow-angle glaucoma or not. But as you ascend, all your fluid-filled spaces equilibrate with ambient pressure, and there is no need for fluid to drain from the eye for the pressure to decrease. I don't understand the statement of the paper's author, but I'm not an ophthalmologist.

 

[DocVikingo]

Hi David,

Yours appears an intelligent and well-reasoned approach to the issue.

At depth the pressure inside the eye does not increase, since, like the rest of the body structures that normally contain no gas, the eye is not compressible. As such, the alterations in ambient pressure inherent in SCUBA itself should pose no risk of rupture to an operated but fully healed eye wall.

As a diver descends, air within the mask compresses and, indeed, if the pressure differential between the inside of the mask and the eye becomes extreme enough, it does risk traumatizing the eyeball (e.g., hyphemia, incisional rupture) and surrounding tissues (e.g., periorbital edema, ecchymosis). For this reason, divers equalize these pressure changes as they move down and up in the water column. I am not aware of any research addressing how close to "normal" this equalization typically achieves. However, a diver who gently and assiduously maintains intra-mask pressure at or about a normal level likely would be at minimal risk of traumatizing the eye, operated or not.

You might find the following DAN piece regarding diving and the eye to be informative:

High-Pressure Ophthalmology: DAN Answers Divers' Most-Asked Questions About Their Eyes

DAN Divers Alert Network : High-Pressure Ophthalmology

Helpful?

Regards,

DocVikingo

 

[headsqueeze]

It is possible that a decrease of i.o.p upon descent noted in this study has its origin in our body's ancestral dive reflexes. Upon ascent w/ a narrow angle, i.o.p. equalization may lag.

[Problems of intraocular pressure in scuba diving (author's transl)]
The reactions of intraocular pressure (i. o. p.), pulse rate, and blood pressure were studied on 30 scuba divers in a pressure tank. Under excess pressures of 2 and 4 atm the i.o.p. showed an average fall of 2-3 mm Hg.
[Problems of intraocular pressure in scuba diving ...[Klin Monatsbl Augenheilkd. 1975] - PubMed Result

[Ocular barostress and barotrauma. A study of 15 scuba divers]
BACKGROUND: During SCUBA-diving, relative changes of the pressure in the diving mask, compared to the environmental pressure, are transmitted to the eye and to the periocular tissue. Barotrauma results from lack of pressure equilibration.
RESULTS: Mean delta-p was 14.8 mbar (-44 to , std.dev. +/- 9), it was not dependent on the diving depth (r2 = 0.0004). Delta-p oscillated between 0 and 25 mbar (0-19 mm Hg), parallel to respiration. Negative delta-p values were 9.5 times more frequent in beginners than in experienced divers. Negative pressure peaks (changes > or = 10 mbar for more than 6 sec) occurred in the beginner group exclusively (p = 0.01).
[Ocular barostress and barotrauma. A study of 15 s...[Klin Monatsbl Augenheilkd. 2001] - PubMed Result

 

[Gene_Hobbs]

Wish I had more to add but there isn't much available in our database either.

This one may be of interest since it addresses high pressure oxygen but it does not touch on effects of immersion with or without a change in external pressure on the eye.

Ersanli et. al. The effect of hyperbaric oxygen on intraocular pressure. Undersea Hyperb Med. 2006 Jan-Feb;33(1):1-4. RRR ID: 5023

 

[David Glasser]

Great group you've got here - thanks for the responses.

Since, posting, I did find the following excellent review article. It does not answer the question of how large the pressure gradient is in divers who are properly equalizing their masks, but it does give some guidelines regarding time off from diving after various ocular surgical procedures. The article cited by Headsqueeze above is somewhat reassuring in that most divers learn to avoid major pressure differentials with experience.

David

Surv Ophthalmol. 1995 Mar-Apr;39(5):347-66.Links
Diving and hyperbaric ophthalmology.Butler FK Jr.
Department of Ophthalmology, U.S. Naval Hospital, Pensacola, Florida, USA.
Exposure of the human body to ambient pressures greater than that at sea level may result in various disorders, some of which have ocular manifestations. Additionally, some eye disorders and postoperative states may be adversely affected by the underwater environment or other hyperbaric exposures. The prevalence of recreational, military, and commercial diving, as well as the medical use of hyperbaric oxygen therapy, requires that ophthalmologists be familiar with the effects of the hyperbaric environment on the normal and diseased eye. The ophthalmology and diving medical literatures were surveyed for publications relating to the ophthalmic aspects of diving and hyperbaric exposures. Underwater optics, underwater refractive correction, and ophthalmic aspects of a fitness-to-dive evaluation are summarized. The evaluation and management of ocular manifestations of decompression sickness and arterial gas embolism are reviewed and guidelines for diving after ocular surgery are proposed.
PMID: 7604359 [PubMed - indexed for MEDLINE]

 

[bleeb]

Out of curiosity, how much of a negative pressure do you figure might start to be an issue? Waving a hand or two around to try an establish an 'upper bounds' for a realistic bad case, if someone managed 1' without equalizing their mask (and it was somehow not connecting well through their sinuses) that would be about 23 mmHg.

 

[tursiops]

It's been 15 years; any updates on this?

Specifically, what is known about scuba diving after implantation of a XEN stent for glaucoma?

 

[Duke Dive Medicine]

It's been 15 years; any updates on this?

Specifically, what is known about scuba diving after implantation of a XEN stent for glaucoma?

Per a provider expert I consulted with just now, there are no issues with diving with it, but a lot depends on how long ago it was placed and how the individual is doing after. Recommend that you (or whoever the recipient is) speak with the ophthalmologist who placed it.

Best regards,
DDM

 

[tursiops]

Per a provider expert I consulted with just now, there are no issues with diving with it, but a lot depends on how long ago it was placed and how the individual is doing after. Recommend that you (or whoever the recipient is) speak with the ophthalmologist who placed it.

Best regards,
DDM

Thanks. I read through a very old review document (1995) by F.K. Butler that was helpful.
My ophthalmologist is clueless. We decide this afternoon whether to do it or not....but I do not want to stop diving! 3 months is fine for post-op, but permanently? However, the choice seems to be blindness....