A new histological evaluation method to detect residual ophthalmic viscosurgical devices for cataract surgery

Abstract

Purpose: To establish a new evaluation method to quantify residual ophthalmic viscosurgical device (OVD) volume and corneal endothelium adhesion properties for phacoemulsification surgery.

Methods: We compared the performance of four OVDs (Viscoat®, Healon5®, Healon® and DisCoVisc®) using porcine eyes. First, OVDs were mixed with fluorescent-conjugated dextrans to render them visible under the microscope. A corneal side port was opened, followed by a continuous curvilinear capsulorhexis, and a corneal tunnel incision was made. OVDs were injected, then the lens was removed using one-handed phacoemulsification. After this procedure, the anterior segment of the eye was isolated via an equatorial incision and the tissue was immediately frozen in shimmering liquid nitrogen. Sagittal slices (20 μm) were cut with a Cryostat from limbus to limbus. Every tenth slide was imaged using a fluorescent microscope with a CCD camera. We evaluated the percentage of the corneal endothelium covered by each OVD as the OVD adhesion to corneal endothelium ratio (OAE ratio) and the volume of residual OVD in the anterior chamber.

Results: Viscoat® showed significantly higher endothelium coverage compared with both Healon® and DisCoVisc®. A statistically larger volume of Healon5® remained in the anterior chamber compared with Healon® and DisCoVisc®.

Conclusion: The new evaluation methods used here provide precise quantitative analysis of OAE ratio and residual OVD volume. These results show that Viscoat® and Healon5® have a high potential for coating the corneal endothelium during phacoemulsification and aspiration surgery.

Keywords: Ophthalmology; Surgery.

Fig. 1

Fluorescence microscopy at 1.25× magnification revealed the anterior segment of the porcine eye. (A) Fluorescent material without dextran was found to leak through the tissue and therefore was not able to properly stain the OVDs.

Fig. 2

Dextran-conjugated fluorescence isothiocyanate allowed us to measure properly stained OVDs by fluorescence microscope at 1.25× magnification.

Fig. 3

Fluorescence microscopy at 1.25× magnification revealed the anterior segment of the porcine eye at the level of the midsection.

Fig. 4

Illustration of the two measurement methods. Residual OVD in the anterior chamber was calculated as the area outlined in red. The OVD adhesion to the corneal endothelium ratio (OAE ratio) was defined as the area of the cornea covered by bidirectional arrows (red color) × 100 %.

Fig. 5

OAE ratio of each OVD type after phacoemulsification. The mean OAE ratios (±figure represents standard deviation) for Viscoat^®, Healon5^®, Healon^®, and DisCoVisc^® were 99 ± 0.28%, 83 ± 2.59%, 60 ± 10.81%, and 66 ± 12.92%, respectively. Significant differences were found between Viscoat® and Healon® and between Viscoat® and DisCoVisc® (p = 0.0037 and p = 0.0095, respectively, Fisher's LSD).

Fig. 6

Residual OVD volume after phacoemulsification. The mean residual OVD volumes (±figure represents standard deviation) for Viscoat^®, Healon5^®, Healon^®, and DisCoVisc^® were 0.56 ± 0.02 ml, 0.86 ± 0.20 ml, 0.18 ± 0.15 ml, and 0.21 ± 0.16 ml, respectively. Significant differences were found between Healon5® and Healon® and between Healon5® and DisCoVisc® (p = 0.0039 and p = 0.0053, respectively, Fisher's LSD).