Underwater Optics
Underwater
Refractive Correction
Sources
for Prescription Dive Masks
Ophthalmic
Considerations in Fitness to Dive Evaluations
Contra-indications
to diving from Eye Problems
Diving
Related Vision Loss
Barotrauma
of the Eye
Decompression
Sickness Involving the Eye
Arterial
Gas Embolism of the Eye
The
Effect of Oxygen Toxicity on the Eye
Hyperbaric
Oxygenation
and the Eye
Diving
After Eye Surgery
Recommended
Waiting Periods Prior to Diving
Fitness to Dive: Eye Problems for the Dive Instructor
The Effect of Water on Optics
Light
rays are scattered and absorbed underwater. The deeper underwater - more
light
is absorbed
At 33 fsw [10 meters] about 20% of light
is
perceived and
at 260 fsw, only 1% of light can be seen.
Silt and particulate matter in water greatly reduce this
light and even at very shallow depths can reduce visibility to one foot
or less.
There is selective absorption
of light wavelengths occurring at varying depths, causing color perception changes.
Red colors disappear first
(longer
wavelengths).
reds disappear at about 30 feet, yellows at 75 feet.
Only blues and greens remain at
depths below 100
feet. [Artificial light reverses this effect.]
Mask Effects
Adjusts the changes
that occur with
refraction of
light by the eye under water.
There is a loss of refracting
power
underwater due
to the water/cornea interface. Air between the mask and cornea preserves the refracting power.
However, as light is refracted
away
by the exit from
the water to the eye - there is a magnification of about 30 % - making objects appear closer than reality.
The mask decreases the amount of
field that is perceived from about 180
degrees to 85 degrees (depending upon the type of mask).The reduction in
the
downward vision is most significant in that it prevents the diver
from
appropriate gear management.
HydroOptix, Double-Dome masks
These masks expand
underwater vision almost 5X vs. flat masks and automatically correct for a
remarkably broad range of myopia.
Contact Source
Jon Kranhouse,
HydroOptix LLC
5631 Mesmer Ave
Culver City, CA
90230
PHONE: 310-636-1700 Xt. 209
FAX: 310-390-8401
TOLL FREE in
USA: (877) WIDE EYE
<http://www.hydrooptix.com>
Underwater
Refractive Correction
Contact Lenses
Soft contact lenses are
preferred. No
corneal edema.
Soft contacts more susceptible to
marine infection.
Use disposable lenses.
Hard lenses cause corneal edema
during decompression
and after dives. [Prevented by the use of a 'fenestrated' hard lens]*
Changes are apparently caused by
nitrogen bubbles
in the pre corneal film of tears resulting in epithelial edema.
A good face mask seal minimizes
loss
of lens during
a dive.
Consciously narrowing the
palpebral
fissure can help
in decreasing the possibility of a contact lens floating off of the
surface
of the eye should the mask become flooded.
Reference:
Cornea-contact lens interaction in the
aquatic
environment. Brown MS; Siegel IM, Department
of Ophthalmology, New York University Medical Center, NY 10016, USA.,
CLAO
J, 23(4):237-42 1997 Oct
*'Fenestrated' refers to a 0.4 mm hole
in the center of the hard lens serving as a channel through which the
tears and bubbles can pass.
Sources
for Prescription Dive Masks
Here
is a Google
Search for Prescription diving masks
Considerations
in Fitness to Dive Evaluations
Guidelines
have been published on medical standards for divers which include
considerations concerning the eye. Visual considerations differ
extensively according to the type of diving being contemplated.
Fitness
to dive evaluations are most often done in one of two settings; either recreational and occupational. The first is an
evaluation
done for a patient who is a sport
diver
and asks his or her personal physician "Is it safe for me to dive?" This requires an evaluation and decision based entirely
on
medical safety considerations for the patient.
The
second type of fitness to dive evaluation is one done in an
occupational
setting in which a patient who is
currently
or hopes to be a military or commercial diver is evaluated by a
physician
who works for the organization in
question, with interests of both the organization and the
patient to
be considered. The physical standards which are established may be
quite
different depending on the mission to be
accomplished
by the diver in each setting.
Obviously
additional questions must be considered in occupational settings.
Economic,
medico legal and liability considerations effect considerations in
decisions
about diving fitness in the occupation setting.
The
fitness to dive considerations for sport divers should focus only on
medical
safety and attempt to address three issues:
(1)
Does the condition impair the individual in such a way as to endanger
himself
or his associates in the hazardous hyperbaric environment (e.g.
inadequate
visual acuity);
(2)
Is the condition one which may be made worse by hyperbaric exposures
(e.g.
neurological residua from
DCS);
(3)
Would hyperbaric exposures possibly result in complications from a
pre-existing
condition (e.g. vision threatening
barotrauma
from diving with intraocular gas).
Contra-indications
to Diving from Eye Problems
- Post-operative gas in the eye
Diving should not be allowed early in
the post-operative
period because of the possibility of gas having been inserted
purposefully
or inadvertently. Boyle's Law dictates that the air will change in
volume
inversely in proportion to the depth and the possibility of injury to
the
eye would be great.
- Hollow orbital implant
The implant would implode at depth,
severely
injuring the orbit and endangering the diver.
- Any acute disorder
Pain, double vision
or decrease in visual acuity would interfere with the
problem solving
and decision making process of the diver.
- Recent eye surgery within the
convalescent period.
- Visual problems from previous DCS
or AGE.
Where there is loss of
vision severe enough
as to make it dangerous for them to function in an underwater
environment.
- Functioning filters (Relative
contraindication)
- Divers who have undergone recent
glaucoma filtering
surgery. A minimum of two months convalescence is recommended
after
this procedure.
- Individuals who have undergone
ophthalmic surgical
procedures should allow an appropriate period for
wound healing before resuming diving. [See chart below]
Diving
Related Vision Loss
Contact lens adherence
due to salt
water with resultant
irritation and blurred vision.
Corneal swelling due to bubbles
under
a rigid gas
permeable contact lens.
Displaced contact lens
Reaction to commercial mask
anti-fog
chemicals leading
to blurred vision, photophobia, tearing and spasm of the eye muscles.
Eye
doctors identify this as keratopathy with the slit lamp. This is easily
prevented by appropriate rinsing of the mask before use.
Ultraviolet keratopathy is caused
by
failure to protect
the eyes from the ultraviolet radiation of underwater welding.
Barotrauma
of the Eye
Normally, the eye is
protected from
barotrauma because
the eye is filled with non compressible fluids, the aqueous and
vitreous
humors.
A mask has air filled space that
is
compressible,
affecting the eye and it's adnexa.
If the diver does not expel gas
through the nose
into the mask on descent, negative pressure
develops inside this space, sucking the eyes and lids toward this
space.
This negative pressure
results in marked lid edema and bruising as well as bleeding under the
conjunctivae of the eyeballs. These changes look a lot worse than they
really are but can be disconcerting to the diver and his buddy.
Hyphema, a more serious injury,
can
occur in the
eyes if the diver becomes unconscious and sinks to a greater depth
without
being able to equalize the mask. This can also result in bleeding under
the periosteum of the bones of the orbit.
Vitreoretinal surgery with air
placed
in the eye
contraindicates diving so long as any of the bubble remains. Pressure
induced
changes in the volume of these bubbles may result in hemorrhage inside
the eye and also may result in partial collapse of the eyeball.
Decompression
Sickness Involving the Eye
Signs and Symptoms
Nystagmus (flicking of
the eyes)
double vision
blank areas in the vision
loss of half the vision in an eye
pain in the eye muscles
blindness
inability to see close up objects
inflammation of the optic
nerve
blockage of the central retinal
artery.
Incidence of Ocular DCS
In two large series was
found to be 7
and 12 % .
Long-term changes in the retinas
is
thought to be
due to blockage of blood vessels of the choroid plexus.
The incidence of these lesions is
directly related
to the length of diving and a history of decompression sickness.
In altitude DCS the most common
neurologic finding
is ophthalmologic
Increased risk if exposed to
altitude
too closely
after diving.
Treatment of Ocular DCS
Recompression to 60 fsw
or deeper and
hyperbaric
oxygen breathing, the sooner the better.
Incomplete response to treatment
and
recurrence of
symptoms following treatment may lead to the infrequent situation where
the eye doctor will be called upon to manage the diver in conjunction
with
the diving medicine specialist.
The diver should be retreated
with
recompression
and hyperbaric oxygen even when there is a considerable delay, since
such
treatment can be successful up to several weeks after the initial
insult.
Arterial
Gas Embolism (AGE) of the Eye
Caused by pulmonary
barotrauma as the
diver ascends,
with bubbles getting into the pulmonary venous system and arterial
circulation
from rupture of alveoli.
This can happen in as little as 4
feet of water if
the diver holds the breath while ascending with compressed air
Ocular symptoms generally come
from
cerebral defects
posterior to the optic chiasm, leading to hemianopias and cortical
blindness.
(Brain)
The gas emboli can also occlude
the
ophthalmic or
central retinal artery resulting in blindness. (Arteries blocked)
The treatment is similar to that
given for DCS - emergent
recompression and hyperbaric oxygen in all cases.
The
Effect of Oxygen Toxicity on the Eye
Manifestations of oxygen Toxicity
Eyelid twitching is the
most commonly
seen manifestation
of O2 toxicity and usually is a warning that a full-blown seizure is
imminent.
blurred vision
visual field constriction
visual hallucinations
transient one-sided loss of
vision
Reversible after termination of
the
O2 exposure.
Treatment
Removal of the O2
source immediately.
No residua unless secondary
trauma or
near-drowning
occur from a convulsion .
Prevented by using appropriate O2
concentrations
at proper depths.
Hyperbaric
Oxygenation and the Eye
Retinitis Pigmentosa
(Investigative Ophthalmology 38; 5713
Abstract
#3296, 1997).
Researchers in Italy are reporting a
breakthrough
treatment for retinitis pigmentosa with the use of hyperbaric oxygen
therapy.
Daily hyperbaric oxygen at 2.2 atmospheres of pressure was employed
among
24 RP patients for two years. The electroretinogram readings of RP
patients
undergoing hyperbaric oxygen treatment improved from 4.86 at the
beginning
of the study to 14.4 at the end of the study. RP patients who did not
undergo
oxygen therapy experienced diminished electroretinograms, beginning
with
an average of 4.92 decreasing to 2.97. Hyperbaric oxygen therapy may
rescue
retinal photoreceptors. This report provides encouraging news to
RP patients since there is no proven treatment for RP save for vitamin
A therapy which only slows down progressive loss of vision as measured
by an electroretinogram and does not improve the ERG.
K.K. Jain, author of The Textbook of
Hyperbaric
Medicine, indicates the retina has the highest rate of oxygen
consumption
of any organ in the body. That hyperbaric oxygen treatment is helpful
in
cases of RP is an anomaly because it has been shown to cause severe
constriction
(narrowing) of retinal blood vessels. The hallmark of RP is poor
retinal
circulation. The constriction of the retinal blood vessels however is
offset
by the greatly increased oxygen carrying capacity of the blood during
treatment
(oxygen saturation increases by 23 percent).
Contrast
Sensitivity
(Undersea & Hyperbaric Medicine
21;
387-90,
1994)
Hyperbaric oxygen treatment improves
contrast
sensitivity (ability to see shades of gray) when administered to
healthy
volunteers. Even though patients with non retinal eye disorders have
experienced
constriction of retinal blood vessels following hyperbaric oxygen
treatment,
when there is a lack of oxygen supply to the retina narrowing of
retinal
blood vessels does not occur.
Other Reports
(New England Journal of Medicine 281;
25-30,
1969)
(Journal French Ophthalmology 10: 381-86,
1987)
The medical literature reveals that
hyperbaric
oxygen treatment has been tried on cases of retinitis pigmentosa as
early
as 1965. A 1987 report in the Journal of French Ophthalmology indicates
hyperbaric oxygen treatment improved the visual acuity of a patient
with
retinitis pigmentosa and macular edema.
Radiation neuritis, optic nerve
(Ophthalmology 93; 1083-88, 1986; Journal
Clinical
Neuro-ophthalmology 113; 98-101, 1993)
Hyperbaric oxygen treatment has been
used as a
rescue remedy for optic nerve damage caused by radiation treatment for
brain tumors.
Hyperbaric oxygen improved vision
among individuals
who experienced a sudden loss of vision due to diminished blood supply
to the optic nerve. Oxygen therapy must be administered early following
onset of the event before shrinkage of the optic nerve occurs. (Arh Hig
Rada Tokaikol 45; 19-24, 1994)
Decreased Vision due to multiple
sclerosis
(New England Journal Medicine 308;
181-86, 1983)
Multiple sclerosis patients undergoing
20 hyperbaric
oxygen treatments experienced temporary improvement of their symptoms
including
visual symptoms.
Recently 100 percent oxygen delivered
at 2 times
atmospheric pressure did not produce a significant improvement in
visual
acuity or peripheral vision among patients suffering from a condition
known
as non arterial anterior ischemic optic neuropathy. (American Journal
Ophthalmology
122; 535-41, 1996)
Glaucoma
Among glaucoma patients, hyperbaric
oxygen has
been shown to expand peripheral vision, an effect which lasted for 3
months.
(Acta Ophthalmologica 71; 315-19, 1993)
The fluid pressure in the eye of
humans and animals
decreases as atmospheric pressure is raised in a hyperbaric chamber.
(Investigative
Ophthalmology 19; 43-48, 1980)
K.K. Jain, author of Textbook of
Hyperbaric Medicine,
reports that hyperbaric oxygen has been used to
successfully treat cases of glaucoma.
Twenty
or more 90 minute treatments at 2 atmospheres of pressure expanded the
visual field among all glaucoma subjects tested. There was no change in
eye fluid pressure.
Retinal artery and vein occlusion
Hyperbaric oxygen treatment combined
with a blood vessel
widening drug (vasodilator) has been shown to improve visual function
among
individuals experiencing retinal artery occlusion. (European Journal
Ophthalmology
3; 89-94, 1993)
Hyperbaric oxygen treatment has been
successfully
used to improve vision among patients with retinal swelling (macular
edema)
and retinal vein occlusion. (Survey of Ophthalmology 39; 347-66, 1995)
Hyperbaric oxygen treatment has been
administered
successfully to patients with central retinal swelling (macular edema)
resulting from retinal vein occlusion. Among 12 patients who were
treated,
10 experienced visual improvement, with median visual acuity improving
from 20/100 to 20/25. The hyperbaric oxygen treatment is believed to
constrict
retinal capillaries and thus decrease leakage of fluid that causes
edema.
(Ophthalmologica 210; 168-170, 1996)
Possible ocular
side effects
HBO2
It has been known that healthy persons
can breathe
oxygen at 3 times normal atmospheric pressure for 3 hours without any
ocular
side effects, but during the fourth hour some begin to experience a
narrowing
of their visual field.
One reported side effect of hyperbaric
oxygen
treatment is the development of myopia (nearsightedness). (Journal
Hyperbaric
Medicine 1; 69-73, 1987) Myopia was first reported in 1978 among 18 of
26 patients undergoing hyperbaric oxygen treatment at 4 atmospheres of
pressure. (Transactions American Ophthalmology Society 76; 118-24,
1976)
Note: Italian doctors only used 2.2 atmospheres of pressure in their
successful
treatment of RP with hyperbaric oxygen.
Dogs exposed to 3 atmospheres of
pressure at 100
percent oxygen developed retinal problems and a reduction in their
electro-retinograms.
Narrowing of the visual field and impairment of central vision has been
recorded among humans undergoing hyperbaric oxygen treatment at 3
atmospheres
of pressure for more than 4 hours. (Science 151; 466-68, 1966)
Captain Frank K. Butler, Jr. of the
U.S. Navy
reviewed the ocular effects of hyperbaric oxygen treatment in a recent
issue of Review of Ophthalmology. Hyperbaric oxygen may induce myopia
(nearsightedness)
at the rate of one quarter diopter change in eyeglass prescription per
week among patients receiving daily hyperbaric oxygen treatment. The
myopia
reverses slowly over a course of many weeks. Cataracts have been
reported
to occur among patients undergoing a prolonged course of daily
hyperbaric
oxygen treatment which may not be reversible following cessation of
treatment,
particularly among adults of advanced age. (Survey of Ophthalmology 39;
347-66, 1995) K.K. Jain indicates cataracts may occur among patients
undergoing
hyperbaric oxygen treatment but that these were seldom observed when
less
than 200 treatments were administered.
K.K. Jain reports that the most useful
role of
hyperbaric oxygen in eye care is the relief of blood vessel
constriction
in central retinal artery occlusion with a success rate as high as 60
percent.
Hyperbaric oxygen does not appear to have a useful role in the
treatment
of diabetic retinopathy. K.K. Jain states "With the pressure and
duration
of exposures used in clinical practice, ocular complications are not a
problem... Hyperbaric oxygen appears to be a safe treatment from the
ocular
point of view." Confirming its safety, hyperbaric oxygen treatment has
been applied in cases of multiple sclerosis with optic neuritis without
loss of vision or narrowing of the visual field.
Free Radicals
(Free Radical Biology & Medicine 6;
505-12,
1989)
Hyperbaric oxygen treatment has been
shown to
adversely affect the electroretinograms (ERGs) of rodents fed a diet
deficient
in vitamin E and selenium. But rodents fed vitamin E alone or vitamin E
plus selenium showed no decreases in their ERGs after 15 weeks of
hyperbaric
oxygen treatment.
Diving
After Eye Surgery
Individuals who have undergone
ophthalmic surgical
procedures should allow an appropriate period for
wound healing before resuming diving.
Factors increasing the risk
of post-operative complications:
Marine organisms may
cause infections
when they contaminate
non-epithelialized wound surfaces of the cornea, sclera, conjunctiva,
or
lid tissues
These pathogens may enter the eye
through unhealed
corneal or scleral wounds and result in vision threatening
endophthalmitis
The risk of infection due to
contact
of the eye with
water is much greater when diving in potentially contaminated ocean,
river,
or lake water than when showering or bathing in chlorinated city
water.
Gas in the anterior chamber or
vitreous cavity.
This may
be affected by changes in pressure and result in vision threatening
intraocular
barotrauma
Negative pressure in the air
space of
a face mask
caused by a mask squeeze.
This may result in subconjunctival hemorrhage, lid
ecchymosis and edema, and could theoretically cause the rupture
of incompletely
healed corneal or scleral wounds.
In chamber dives, only gas in the
eye
remains a consideration.
There are no controlled studies
specifically
addressing the requisite length of convalescence before a return to
diving from any type of eye surgery.
The recommendations below are based on the application of wound healing
observations in other studies and on clinical experience.
Also, it is unknown whether scuba has any relationship in
causing or contributing to conditions such as retinal detachment in the
normal eye. Concerned divers with signs and symptoms of visual problems
are advised to seek advice from their eye doctors.
A. Corneal surgery
Full thickness incisions
Very little healing is
noted in the
first week, followed
by a rapid rise to about 30% of normal strength at 1 month.
Wound strength then gradually
increases to approximately
50% of normal by 3 to 6 months.
Penetrating keratoplasty in which
full thickness
incisions are made in the cornea should be followed by a six month
convalescent
period.
Radial and astigmatic keratotomy
- Do not entail
full thickness corneal incisions or prolonged topical steroid therapy,
may be allowed to dive after three months.
- The possibility of
barotrauma induced
rupture of
a corneal wound is a theoretical possibility after any of the above
procedures,
but would occur only in the setting of an uncommonly encountered face
mask
squeeze.
