Literature Review: Humidified Air During Vitreoretinal Surgery

Author Eyes Methods/Results Conclusions In a consecutive nonrandomized series of 45 operations on 35 eyes of 34 patients with full-thickness macular hole, the  Dehydration injury of the nerve fiber layer during the fluid-air Welch1 surgical method was changed with postoperative visual 35 eyes of 34 patients exchange should be considered as a possible cause of visual field AJO 1997 field testing performed. The incidence and location of the defect after pars plana vitrectomy for macular hole. post-operative visual field defect was affected only by changing the location of the infusion cannula.

Goldmann perimetry was used to measure the visual fields of patients who underwent vitrectomy to manage idiopathic  Passing air used for fluid–air exchange through water seems to full-thickness macular holes using either room air (Group 1, prevent visual field defects after vitrectomy for macular hole retrospective review of 39 patients) or humidified air surgery. Ohji2 (Group 2, prospective study of 33 patients) for fluid–air  Visual field defects that occur after room air is used may result from 72 patient eyes AJO 1999 exchange. Group 1, Dry air eyes: 9 of 39 eyes (23%) were desiccation of the retina by room air. found to have peripheral visual field loss. Group 2,  The authors strongly recommend that air used for fluid-air Humidified air eyes: no eyes had a peripheral visual field exchange be passed through water before infusion into the eye to loss. The difference between these groups was statistically prevent visual field defects after vitrectomy. significant.

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 Welch3 None. exists that dehydration or desiccation of the nerve fiber layer is responsible for the visual field defect in some patients after macular AJO 1999 Letter to the Editor re: 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 Ohji above 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.”

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 Ohji4 None. parameters may be sufficient to prevent the occurrence of postoperative visual field defects after vitreoretinal surgery with fluid-air AJO 1999 Author Reply 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.”

 Significant water losses can occur from eyes undergoing fluid-air The absolute water content of air was measured in a series exchange. of 6 eyes undergoing fluid-air exchange during macular  Humidifying the infused air can substantially reduce the dehydrating Vote5 6 patient eyes hole surgery. Results showed that humidifying the air effect during an air exchange. BJO 2004 during vitreoretinal surgery reduced the rate of water loss  This outcome may have a beneficial effect in reducing cataract by nearly 90%. formation and visual field defects associated with macular hole surgery.

IRIDEX – Literature Review: Humidified Air during Vitreoretinal Surgery LT0518 04/20/10. Page 1 of 4 Author Eyes Methods/Results Conclusions Intraocular humidity in the vitreous cavity was recorded  Water loss in living eyes is greater than the rate of for 2 minutes after the eyes had been filled with either aqueous production. 6 artificial eyes, Eter6 humidified air (75% humidity) or dry air (8% humidity).  Evaporation stress has a damaging effect on the surrounding 6 enucleated pig eyes, Graefe’s 2006 Results showed dry air deprives the retinal tissue of tissues. 10 patient eyes humidity, which is lost into the vitreous cavity, which  Until proven otherwise the use of humidified air is therefore can be reduced by using humidified air. advocated.

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  Infusion of humidified air further protects corneal endothelium without using any viscoelastic agent. Corneas obtained during vitreal fluid-air exchange. Cekic7 Rabbit eyes from rabbits undergoing surgery were compared with AJO 2003  Humidified air seems to increase the retentive ability of viscoelastic corneas obtained from rabbits not undergoing surgery. substances by keeping the surface hydrated, and maintains the Corneas exposed to dry air displayed greater irregularity functional integrity of endothelial cells better. 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.

Rabbits undergoing pars plana vitrectomy and lensectomy were perfused with either dry or humidified air during fluid– air exchange for designated durations. Humidified air- exposed endothelial cells had a relatively irregular, less  Dry air stress during fluid-air exchange causes significant interdigitated, and more ruffled appearance of the cell Cekic8 immediate alterations in monolayer appearance, actin cytoskeleton, Rabbit eyes borders; fewer microvilli on the cell surface; and pitting on AJO 2002 and barrier function of corneal endothelium in aphakic rabbit eyes. the cell borders. Corneas exposed to dry air displayed a Use of humidified air largely prevents these alterations. 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)

Fourteen pigmented rabbits underwent two-port pars plana lensectomy and vitrectomy. Seven eyes were insufflated Cekic9 with dry air; the other 7 eyes with humidified air. The pupils  Humidification of air infusion during vitrectomy slows the rate of Rabbit eyes Retina 2001 remained larger in the eyes exposed to humidified air miosis in an aphakic rabbit model. compared with dry air over the first 7 minutes during fluid- air exchange.

IRIDEX – Literature Review: Humidified Air during Vitreoretinal Surgery LT0518 04/20/10. Page 2 of 4 Author Eyes Methods/Results Conclusions Vitrectomy and fluid-air exchange was carried out using 16 eyes of 8 pigmented rabbits. One eye of each rabbit was  Use of a humidifier during fluid-air exchange prolongs exposed to dry air and the fellow eye received humidified intraoperative lens clarity in the rabbit model, suggesting that air using an intraocular air humidifier. In each case, the humidified air should prolong lens clarity during phakic fluid-air percent humidity of the intraocular air was measured using exchange in patients. Harlan10 an in-line hygrometer. Elapsed time from initial air entry to  Use of humidified air during vitrectomy and fluid-air exchange may Rabbit eyes Archives 1999 lens feathering was recorded for each eye, with the retard the intraoperative loss of lens clarity, promoting better surgeon-observer unaware of the percent humidity of the visualization of the posterior segment and enhancing surgical air infusion. In each rabbit, use of humidified air resulted in performance. a delay in lens feathering (P<.02), with an overall increase Note: Retina Labs (previously American Medical Devices, Inc.) humidifier in time to feathering of 80% for humidified air vs. room air. was used. (See Figure 2)

A standard air infusion line used in vitreoretinal surgery  To eliminate dehydration as a cause of intraocular morbidity, one was evaluated with and without the MoistAir™ device. The must first saturate the infused air. If the visual field defects and effect of humidification, pressure, and resistance to flow None. other complications are eliminated, this would be good evidence for Vote11 were assessed at varying points in the air line infusion Laboratory saturating infused air. Retina 2002 system. When used together, MoistAir and a standard Measurements  As infusion pressure (flow rate) influences dehydration rate, unless 20G infusion line reduced flow rate and infusion pressure by one third. MoistAir was found to add 6.5 mg/L water saturated air is used, infusion pressure cannot be considered an content to the air infusion line system. independent variable in the analysis of field defects.

Figure 1. Scanning electron microscopy (SEM) micrographs of the normal, dry, Figure 2. Posterior lens surface under magnification.10 and humidified air exposed corneal endothelial cells.8

Healthy lens Occurrence of feathering on the lens A: Normal B: 20 minunte humidified C: 20 minute dry air-exposed 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 pitting on the cellular 8 surface.IRIDEX – Literature Review: Humidified Air during Vitreoretinal Surgery 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