Literature Review: Humidified Air During Vitreoretinal Surgery
Author
Welch1
AJO 1997
Ohji2
AJO 1999
Welch
3
AJO 1999
Ohji4
AJO 1999
Vote5
BJO 2004
Eyes
Methods/Results
Conclusions
35 eyes of 34 patients
In a consecutive nonrandomized series of 45 operations on
35 eyes of 34 patients with full-thickness macular hole, the
surgical method was changed with postoperative visual
field testing performed. The incidence and location of the
post-operative visual field defect was affected only by
changing the location of the infusion cannula.
 Dehydration injury of the nerve fiber layer during the fluid-air
exchange should be considered as a possible cause of visual field
defect after pars plana vitrectomy for macular hole.
72 patient eyes
Goldmann perimetry was used to measure the visual fields
of patients who underwent vitrectomy to manage idiopathic
full-thickness macular holes using either room air (Group 1,
retrospective review of 39 patients) or humidified air (Group
2, prospective study of 33 patients) for fluid–air exchange.
Group 1, Dry air eyes: 9 of 39 eyes (23%) were found to
have peripheral visual field loss. Group 2, Humidified air
eyes: no eyes had a peripheral visual field loss. The
difference between these groups was statistically
significant.
 Passing air used for fluid–air exchange through water seems to
prevent visual field defects after vitrectomy for macular hole
surgery.
 Visual field defects that occur after room air is used may result from
desiccation of the retina by room air.
 The authors strongly recommend that air used for fluid-air
exchange be passed through water before infusion into the eye to
prevent visual field defects after vitrectomy.
None.
Letter to the Editor re:
Ohji above
Dr. Welch congratulates Dr. Ohji for having presented an innovative method for avoiding the visual field defect after vitrectomy for
macular hole. Dr. Welch shares his refined surgical techniques for treating macular holes, and comments, “Strong evidence now
exists that dehydration or desiccation of the nerve fiber layer is responsible for the visual field defect in some patients after macular
hole surgery. I do not believe it is necessary to use a humidifier to prevent a field defect in this type of surgery; changing the surgical
technique appears to be sufficient. A humidifier may be more useful in cases where prolonged air infusion during intraocular
manipulations (such as with endolaser treatment) is needed.”
None.
Author Reply
Dr. Ohji reviews three parameters of air flow that may contribute to retinal desiccation: humidity, flow rate, and duration; and relates
these parameters to Dr. Welch’s treatment techniques. He concludes, “Although careful attention to one or two of the three
parameters may be sufficient to prevent the occurrence of postoperative visual field defects after vitreoretinal surgery with fluid-air
exchange, at present it is not clear which parameter is most important in the pathogenesis of this complication; therefore, all three
parameters should be taken into account. Air should be humidified before infusion into the eye, the air pressure should not be set too
high, and scleral plugs should be used frequently.”
6 patient eyes
The absolute water content of air was measured in a series
of 6 eyes undergoing fluid-air exchange during macular
hole surgery. Results showed that humidifying the air
during vitreoretinal surgery reduced the rate of water loss
by nearly 90%.
IRIDEX – Literature Review: Humidified Air during Vitreoretinal Surgery
 Significant water losses can occur from eyes undergoing fluid-air
exchange.
 Humidifying the infused air can substantially reduce the
dehydrating effect during an air exchange.
 This outcome may have a beneficial effect in reducing cataract
formation and visual field defects associated with macular hole
surgery.
LT0518 04/20/10. Page 1 of 4
Author
Eter6
Graefe’s 2006
Cekic7
AJO 2003
Cekic8
AJO 2002
Cekic9
Retina 2001
Eyes
Methods/Results
Conclusions
6 artificial eyes,
6 enucleated pig eyes,
10 patient eyes
Intraocular humidity in the vitreous cavity was recorded
for 2 minutes after the eyes had been filled with either
humidified air (75% humidity) or dry air (8% humidity).
Results showed dry air deprives the retinal tissue of
humidity, which is lost into the vitreous cavity, which
can be reduced by using humidified air.
 Water loss in living eyes is greater than the rate of
aqueous production.
 Evaporation stress has a damaging effect on the surrounding
tissues.
 Until proven otherwise the use of humidified air is therefore
advocated.
Rabbit eyes
Rabbit eyes undergoing pars plana lensectomy and
vitrectomy were insufflated with either dry or humidified
air for 20 minutes following introduction of either Opegan
or Viscoat into the anterior chamber. In two other groups
of rabbit eyes, the same procedure was performed
without using any viscoelastic agent. Corneas obtained
from rabbits undergoing surgery were compared with
corneas obtained from rabbits not undergoing surgery.
Corneas exposed to dry air displayed greater irregularity
of cell shape, and cell borders accompanied by raised
apical flaps. The intercellular junctions appeared loose
and separated with clefts. Cell surfaces were devoid
of microvilli.
 Infusion of humidified air further protects corneal endothelium
during vitreal fluid-air exchange.
 Humidified air seems to increase the retentive ability of viscoelastic
substances by keeping the surface hydrated, and maintains the
functional integrity of endothelial cells better.
Rabbit eyes
Rabbits undergoing pars plana vitrectomy and lensectomy
were perfused with either dry or humidified air during fluid–
air exchange for designated durations. Humidified airexposed endothelial cells had a relatively irregular, less
interdigitated, and more ruffled appearance of the cell
borders; fewer microvilli on the cell surface; and pitting on
the cell borders. Corneas exposed to dry air displayed a
loss of surface microvilli and extensive ruffling of their
apical cellular flaps; pitting on cellular surface and on the
borders; and no clear areas of separation were visible.
(See Figure 1)
 Dry air stress during fluid-air exchange causes significant
immediate alterations in monolayer appearance, actin cytoskeleton,
and barrier function of corneal endothelium in aphakic rabbit eyes.
Use of humidified air largely prevents these alterations.
Rabbit eyes
Fourteen pigmented rabbits underwent two-port pars plana
lensectomy and vitrectomy. Seven eyes were insufflated
with dry air; the other 7 eyes with humidified air. The pupils
remained larger in the eyes exposed to humidified air
compared with dry air over the first 7 minutes during fluidair exchange.
 Humidification of air infusion during vitrectomy slows the rate of
miosis in an aphakic rabbit model.
IRIDEX – Literature Review: Humidified Air during Vitreoretinal Surgery
LT0518 04/20/10. Page 2 of 4
Author
Harlan10
Archives 1999
Vote11
Retina 2002
Eyes
Rabbit eyes
None.
Laboratory
Measurements
Methods/Results
Conclusions
Vitrectomy and fluid-air exchange was carried out using 16
eyes of 8 pigmented rabbits. One eye of each rabbit was
exposed to dry air and the fellow eye received humidified
air using an intraocular air humidifier. In each case, the
percent humidity of the intraocular air was measured using
an in-line hygrometer. Elapsed time from initial air entry to
lens feathering was recorded for each eye, with the
surgeon-observer unaware of the percent humidity of the
air infusion. In each rabbit, use of humidified air resulted in
a delay in lens feathering (P<.02), with an overall increase
in time to feathering of 80% for humidified air vs. room air.
(See Figure 2)
 Use of a humidifier during fluid-air exchange prolongs
intraoperative lens clarity in the rabbit model, suggesting that
humidified air should prolong lens clarity during phakic fluid-air
exchange in patients.
 Use of humidified air during vitrectomy and fluid-air exchange may
retard the intraoperative loss of lens clarity, promoting better
visualization of the posterior segment and enhancing surgical
performance.
A standard air infusion line used in vitreoretinal surgery
was evaluated with and without the MoistAir™ device. The
effect of humidification, pressure, and resistance to flow
were assessed at varying points in the air line infusion
system. When used together, MoistAir and a standard
20G infusion line reduced flow rate and infusion pressure
by one third. MoistAir was found to add 6.5 mg/L water
content to the air infusion line system.
 To eliminate dehydration as a cause of intraocular morbidity, one
must first saturate the infused air. If the visual field defects and
other complications are eliminated, this would be good evidence for
saturating infused air.
 As infusion pressure (flow rate) influences dehydration rate, unless
saturated air is used, infusion pressure cannot be considered an
independent variable in the analysis of field defects.
Figure 1. Scanning electron microscopy (SEM) micrographs of the normal, dry,
and humidified air exposed corneal endothelial cells.8
Note: Retina Labs (previously American Medical Devices, Inc.) humidifier
was used.
Figure 2. Posterior lens surface under magnification.10
Healthy lens
A: Normal
B: 20 minunte humidified
air-exposed
Occurrence of feathering on the lens
C: 20 minute dry air-exposed
(A) Normal rabbit corneal endothelial cells displaying a uniform hexagonal appearance with regular
interdigitated cell borders and distinct microvilli on the cell surface. Note that the cell junctions are
always flat and do not protrude above the cell surface (scale bar, 15 μm). (B) 20 minute humidified
air-exposed endothelial cells with relatively irregular and less interdigitated more ruffled cell
borders. Some pitting is visible on cellular borders. (C) 20 minute dry air-exposed endothelial cells
showing more stressed appearance. Cells were accompanied by pronounced apical flaps. The cell
borders show lifting off the surface. Note the open clefts between the cells together with extensive
8
IRIDEX
– Literature
Review:
Humidified
Air during Vitreoretinal Surgery
pitting on
the cellular
surface.
LT0518 04/20/10. Page 3 of 4
Bibliography
1. Welch JC. Dehydration injury as a possible cause of visual field defect after pars plana vitrectomy for macular hole. Am J Ophthalmol
1997;124(5):698-9.
2. Ohji M, Nao IN, Saito Y, Hayashi A, Tano Y. Prevention of visual field defect after macular hole surgery by passing air used for fluid-air exchange
through water. Am J Ophthalmol 1999;127(1):62-6.
3. Welch JC. Letter to the Editor: Prevention of visual field defect after macular hole surgery by passing air used for fluid-air exchange through water.
Am J Ophthalmol 1999;128(3):396-7.
4. Ohji M, Okada AA, Tano Y. Author Reply: Prevention of visual field defect after macular hole surgery by passing air used for fluid-air exchange
through water. Am J Ophthalmol 1999;128(3):397.
5. Vote BJ, Russell MK, Newland A, Polkinghorne PJ. The evaluation of a humidifying device for vitreoretinal surgery. Br J Ophthalmol
2004;88(12):1582-4.
6. Eter N, Brinken R, Garbe S, Spitznas M. Intraocular humidity immediately after fluid-air exchange in pars plana vitrectomy. Graefes Arch Clin Exp
Ophthalmol 2006;244(3):305-8.
7. Cekic O, Ohji M, Zheng Y, Hayashi A, Kusaka S, Tano Y. Experimental study of viscoelastic in the prevention of corneal endothelial desiccation
injury from vitreal fluid-air exchange. Am J Ophthalmol 2003;135(5):641-7.
8. Cekic O, Ohji M, Hayashi A, Fang XY, Kusaka S, Tano Y. Effects of humidified and dry air on corneal endothelial cells during vitreal fluid-air
exchange. Am J Ophthalmol 2002;134(1):75-80.
9. Cekic O, Ohji M, Hayashi A, Fang XY, Kusaka S, Tano Y. Humidified air effect on pupil size during fluid-air exchange. Retina 2001;21(5):529-31.
10. Harlan JB, Jr., Lee ET, Jensen PS, de Juan E, Jr. Effect of humidity on posterior lens opacification during fluid-air exchange. Arch Ophthalmol
1999;117(6):802-4.
11. Vote BJ, Newland A, Polkinghorne PJ. Humidity devices in vitreoretinal surgery. Retina 2002;22(5):616-21.
IRIDEX acquired Retina Labs April 2010.
IRIDEX and the IRIDEX logo are registered trademarks, and MoistAir is a trademark of IRIDEX Corporation.
IRIDEX – Literature Review: Humidified Air during Vitreoretinal Surgery
LT0518 04/20/10. Page 4 of 4