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.
Ohji2 AJO 1999
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.
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.”
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.”
Vote5 BJO 2004
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%.
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.
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.
Evaporation stress has a damaging effect on the surrounding tissues.
Until proven otherwise the use of humidified air is therefore 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
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
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.
Cekic8 AJO 2002
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 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.
Cekic9 Retina 2001
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 fluid-air exchange.
Humidification of air infusion during vitrectomy slows the rate of miosis in an aphakic rabbit model.
Harlan10 Archives 1999
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.