|Year : 1999 | Volume
| Issue : 4 | Page : 237-240
Retained viscoat and intraocular pressure after phaceomulsification
P Watts, M Austin
Department of Ophthalmology, Singleton Hospital, Swansea, UK
Department of Ophthalmology, Singleton Hospital, Swansea, UK
Source of Support: None, Conflict of Interest: None
Purpose: A single blind prospective randomised study to determine the effect of Viscoat retained in the eye on intraocular pressure (IOP) after phacoemulsification.
Methods: 82 patients were randomly selected to receive either Viscoat, a viscoelastic composed of 3% sodium hyaluronate (mol wt 500,000 daltons), and 4% chondroitin sulfate (mol wt 25,000 daltons) or Provisc, a viscoelastic compound composed of 1% sodium hyaluronate (mol wt 4,00,000 daltons) during phacoemulsification. In those patients receiving Viscoat the viscoelastic in the anterior chamber only was removed, whereas in those receiving Provisc attempts were made to remove the material entirely. The IOP was measured on the first postoperative day, 16-20 hours after surgery.
Results: The mean postoperative IOP in the Viscoat group was 22.37 ± 9.0 mmHg and in the Provisc group was 19.67 ± 6.95 mmHg. Five patients in the Viscoat group had pressure elevations above 30 mmHg as opposed to three in the Provisc group.
Conclusions: The two viscoelastics cause equivalent pressure elevations postoperatively. In the Viscoat group there were five patients with IOPs above 30 mmHg. We recommend that Viscoat should be aspirated from both the anterior chamber and the capsular bag following routine phacoemulsification.
Keywords: Viscoat, Provisc, phacoemulsification, intraocular pressure
|How to cite this article:|
Watts P, Austin M. Retained viscoat and intraocular pressure after phaceomulsification. Indian J Ophthalmol 1999;47:237-40
Viscoelastics are routinely used during cataract surgery to facilitate anterior segment manipulations while protecting the endothelium and maintaining the depth of the chambers., The coatability of Viscoat which adheres to the positively charged endothelium (because of its sulfated carbohydrate moieties), favours its selection over other agents such as Provisc, to protect the corneal endothelium., Clinically retained Viscoat has been reported to cause less postoperative pleomorphism of the endothelial cells. However, the benefits of leaving Viscoat in the eye must be weighed against the potential ability of this agent to raise the intraocular pressure (IOP). As Viscoat has a smaller molecular weight than Provisc, it should theoretically be cleared from the anterior chamber without significant pressure elevations. Retained sodium hyaluronate after cataract surgery has been associated with a 33% elevation in the postoperative IOP, as compared to 11% when the substance has been aspirated.
Viscoat has been reported to cause only mild and transient IOP elevations as compared to sodium hyaluronate.,,, We conducted a prospective randomised single blind study of 82 patients to compare the effects of the two substances on the postoperative IOP.
Materials and Methods
Eighty two consecutive patients were randomly selected to receive either Provisc or Viscoat in one eye during phacoemulsification for cataract removal. Informed written consent was obtained from all patients, and the study was approved by the local ethics research committee of Iechyd Morgannwg Health, Wales, UK.
All patients had a detailed ophthalmic examination preoperatively. Patients with glaucoma, pseudoexfoliation or corneal guttata were excluded. The mean of three preoperative IOP measurements was taken. The procedure was performed by consultants and experienced higher surgical trainees under consultant supervision in equal numbers. No attempt was made to mask the randomisation of the viscoelastic during the operation due to the different handling characteristics of the two agents.
In all cases a standardised routine phacoemulsification was performed through a 3.2 mm corneal tunnel incision, with a continuous curvilinear capsulorhexis, using the nucleofractis technique. The incision was enlarged to 5 mm to insert an intraocular lens (IOL), whose optic was 5 mm in diameter.
In cases where Provisc was used, every effort was made to aspirate it from the eye in its entirety after the insertion of the IOL, by depressing the lens with the automated irrigation aspiration handle at a vaccum of 500 mmHg. In the cases where Viscoat was used, only a minimal amount of the viscoelastic was aspirated from the anterior chamber with the phaco handpiece at a vaccum of 100 mmHg; no attempt was made to aspirate the material retained in the capsular bag. This minimal aspiration was carried out only to confirm the position of the IOL in the bag. The fact that Viscoat was retained in the eye was confirmed by the presence of cavitation bubbles lining the endothelium. A single 10-0 monofilament suture was used to routinely close the incision.
Patients who had a posterior capsule rupture or those who were converted to an extracapsular cataract extraction during the procedure were excluded from subsequent analysis. The time taken for phacoemulsification and the mean power used were recorded. The surgeon's comments about the procedure with particular reference to the handling of the two viscoelastics were noted.
None of the patients received a prophylactic ocular hypotensive agent after surgery. Postoperative lOPs were measured with a Goldman's applanation tonometer at the first dressing at 16-20 hours, the examiner being masked as to which group the patient belonged.
A total of 68 patients (26 males and 42 females) were eligible for analysis (33 patients receiving Provisc and 35 Viscoat). Patient demographic characteristics, preoperative and postoperative IOP, phacoemulsification duration, and mean power are shown in Table. Fourteen patients were excluded for the following reasons: posterior capsule rupture (8 patients; 5 in Provisc group, 3 in Viscoat group), conversion to extracapsular cataract extraction (2 patients), and insufficient data recorded (4 patients).
Mean ages were 77 ± 8 years for the Viscoat group and 75 ± 15 years for the Provisc group (p=0.64, NS). The mean pre-operative lOPs for the two groups were 15.8 ± 3.9 mmHg (Viscoat) and 17 ± 3 mmHg (Provisc) (p=0.35, NS). The morphology of the cataracts was similar in the two groups (Lens opacity classification).
The mean ultrasound time was 2.86 ± 1.98 minutes and the mean percentage of power was 21.2 ± 12% in the group of patients for whom Viscoat was used; the corresponding values for the Provisc group were 2.62 ± 2.14 minutes and 17 ± 13%.
There were no significant differences in the postoperative clinical appearances of corneal clarity, or anterior chamber activity in the eyes in the two groups according to observations of the masked examiners.
The mean postoperative IOP was 22.3 ± 9.0 mmHg for patients receiving Viscoat and 19.6 ± 6.9 mm Hg for those receiving Provisc. The mean change in IOP between the two groups was 3.09 ± 6.2 mmHg and 2.6 ± 2.13 mmHg (p>0.05,NS, students' t test).
Five patients (5/35) in the Viscoat group had IOP elevation above 30 mmHg as opposed to three patients (3/33) in the Provisc group; however, the difference between the two groups was not significant (p=0.2, NS Fisher's exact test). The highest postoperative IOP recorded was 50 mmHg in the Viscoat group and 42 mmHg in the Provisc group. These two eyes were treated by anterior chamber decompression through the side-port incision.
The two agents differed in their handling characteristics, with the surgeon reporting difficulty with visualisation in five patients in the Viscoat group. In each case cavitation bubbles became impacted in the Viscoat which coated the endothelium.
Statistical analysis was performed using the SPSS Windows package. The two groups were compared using the two-tailed 't' test (Table). Multiple regression analysis did not reveal any correlation between elevated postoperative IOP and the ultrasound time and power, the age of the patient, or the drug used.
In our study comparable postoperative IOPs were noted in the two groups of patients despite the retention of viscoelastic in the Viscoat group. The IOP was measured at 16-20 hours, it tends to peak at this stage. The patients were well matched for all variables which included age, gender, preoperative IOP, ultrasound time, and power. None of the variables mentioned had any statistically significant effect on the postoperative IOP.
The two substances handled differently and this may be directly related to the greater viscosity of Viscoat., For the same reason it is more difficult to aspirate Viscoat completely from the eye. Relatively poorer visualisation during phacoemulsification may be related to the tendency for Viscoat to be retained in the anterior chamber, thereby trapping cavitation bubbles or debris which can then obstruct the surgeon's view. Indeed, the increased manipulation required to remove Viscoat from the eye may account for the increased endothelial cell loss reported by some authors.
While chondroitin sulfate used alone has been shown to match sodium hyaluronate in corneal protection and postoperative IOP elevations, it is not as viscous as a mixture of the two compounds and therefore affords less corneal protection.,
It may be argued that some of the Provisc might have been retained in the eye as there was no objective method to assess whether it was entirely removed. However, it has been well established that it is a cohesive viscoelastic and is easily removed in its entirety with a high vacuum by depressing the IOL with the irrigation handpiece. Viscoat is a dispersive viscoelastic and hence requires meticulous removal in segments with the phaco handpiece with a large port and high vacuum. In our series only a minimal amount of Viscoat was removed from the anterior chamber just above the optic of the IOL, to confirm its correct placement in the capsular bag. The fact that most of the Viscoat was retained in the anterior chamber was confirmed by the presence of cavitation bubbles lining the corneal endothelium. It has been shown that when Viscoat and Healon are used under identical conditions, gross detectable amounts of Viscoat are retained in the eye, while no detectable Healon is retained.
Though not statistically significant, 14.2% of the patients had postoperative IOPs raised above 30 mmHg in the Viscoat group in comparison to 9.1% in the Provisc group. Studies comparing Viscoat aspirated and not aspirated have shown a higher percentage of patients with higher IOPs when Viscoat was not aspirated. Other studies comparing retained and removed Occucoat and Viscoat showed a (statistically) significantly lower amount of Viscoat was removed from the anterior chamber. However, other studies have shown that this is not true, and hypothesise that the elevation of the postoperative IOP is not related to retention or removal of the viscoelastic, but to actual surgical procedure. The lower molecular weight of Viscoat allows it to be retained in the anterior segment during the procedure and dispersed from the eye better than higher molecular-weight compounds. Provisc has greater cohesiveness, hence it tends to flow out of the eye during the procedure and when retained in the eye is not dispersed as easily as a lower molecular-weight substance like Viscoat.
Some studies that reported no significant elevations in postoperative IOP have used larger incisions to phacoemulsify the lens and in addition a capsulotomy with a can-opener technique. Our study used a continuous curvilinear capsulorhexis with a 5 mm incision, which perhaps allowed inadvertent retention of some of the Provisc in the bag. In addition, smaller incisions have been reported to be associated with higher mean postoperative IOP. In conclusion, both Viscoat and Provisc cause comparable postoperative IOP elevation, even when only Viscoat is retained in the eye. IOPs above 30 mmHg occur in both groups; hence it is recommended that every effort should be made to aspirate the viscoelastic at the end of the procedure.
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