Nozzle tip damage in three generations of intraocular lens injector models: an experimental laboratory study

The tested articles were summarized in Supplemental Table 1.

Emerald cartridge with Unfolder handpiece, a screw-style injector model, was introduced in 2011. The metal handpiece and the plastic cartridge need to be manually loaded by surgeons or theatre staffs before use.

iTec, a preloaded injector model, was introduced in 2015. It is a screw-style injector model.

Simplicity, a preloaded injector model, was introduced in 2019. It is a screw-style injector model.

Collection of the injectors was performed in the same manner as described in our earlier study [5]. Fifty-nine IOL injectors of three models were used for IOL implantation in a series of routine, uncomplicated cataract surgeries at the Heidelberg University Eye Hospital. One experienced surgeon (GUA) performed all the surgical operations. The microscopic image for one unused IOL injector from each model was shown in Fig. 1. Incisions were either 2.4 mm or 2.5 mm and were all clear corneal incisions. The range for IOL power was from + 15D to + 26D. In all cases, the injectors were first primed with 1% ophthalmic viscosurgical device (OVD). At the end of each implantation, a gross examination was performed under the microscope to determine whether the IOL had been damaged. After each surgery session, the used injectors were collected from the operation room and sent to our laboratory. Nozzles were immersed in the distilled water for ten minutes to remove the residual OVD and then dried by the air. Attention was paid not to damage the tips of the injector nozzles while handling.

After air drying, the nozzles were examined using an optical microscope (Olympus BX50, Olympus K.K.). Each nozzle tip was first inspected in the "bevel down" and "bevel up" orientations, followed by examination of the two lateral orientations to identify any damage to the nozzle tip. Photographs of damage were then taken under microscope.

To obtain a cross-sectional surface for each injector model, the nozzle tip of each unused injector model was cut with a razor blade at the point where the bevel angle began. Photographs of the cross-sectional surfaceswere taken under a microscope (Olympus BX50, Olympus K. K.). The parameters (i.e., diameters) of the cross-section surface were measured from an IOL photograph taken under the microscope at the same magnification as the cross-sectional surface, which served as a standard for calibrating the measurements. Image J software (version 1.52a, NIH, Bethesda, Maryland, USA) was used to measure the parameters of the cross-sectional surfaces of the nozzle tips. First, the known diameter of the IOL optics (6 mm) was taken as a reference, and the diameter on the image was measured in pixels. Second, the arithmetic ratio of pixels to millimeters was calculated. Third, the diameters of cross-sectional surfaces were measured on the image in pixels and then converted to millimeters using the arithmetic ratio. The inner and outer cross-sectional areas were calculated using the formula: A = πab (a = cross-sectional horizontal radius, b = cross-sectional vertical radius). The tip angles of three injector models were measured using Image J software (Fig. 1). The thickness of the nozzle tip was determined as the difference between the outer cross-sectional radius and the inner cross-sectional radius and calculated according to the formula: \(\mathrm{Thickness}=\frac{\left(\mathrm{a}1-\mathrm{a}2\right)-(\mathrm{b}1-\mathrm{b}2)}{2}\) (a1 = outer cross-sectional horizontal radius, a2 = inner cross-sectional horizontal radius, b1 = outer cross-sectional vertical radius, b2 = inner cross-sectional vertical radius). (As marked by the purple lines in Fig. 2).

According to our scoring system [5], the damage observed on the injectors was classified into the following six grades.

Each damage grade was assigned a score from 0 to 5 (i.e., Grade 0 was assigned to score 0, Grade 5 was assigned score 5, etc.), and the total damage scores for each injector system was the sum of scores for all injectors in that model. The total damage scores for each injector system were calculated and compared.

Nozzle tip parameters for all injector models are summarized in Table 1. All three injector groups had a round cross-sectional surface. In Emerald, both the outer and inner cross-sectional diameters were relatively larger, while iTec and Simplicity had almost identical cross-sectional diameters. Representative microscopic images of cross-sectional surfaces for all injector models are shown in Fig. 2. Emerald showed a smaller nozzle tip thickness (0.13 mm), whereas the other 2 groups had the same nozzle tip thickness (0.17 mm). The tip angle for three injector models was: 35° (Emerald), 45° (iTec), and 45° (Simplicity).

Representative microscopic images of each damage classification in each injector group are shown in Fig. 3. The distribution of damage profiles of three injector models is shown in Fig. 4. iTec and Simplicity had a similar distribution of damage (mainly slight scratches and deep scratches). In Emerald, slight scratches (3, 27.28%), deep scratches (4, 36.36%), and extensions (4, 36.36%) were observed. For iTec, only slight scratches (11, 52.38%) and deep scratches (10, 47.62%) were observed. For Simplicity, no damage (2, 7.41%), slight scratches (12, 44.44%), deep scratches (11, 40.74%), and extension (2, 7.41%) were observed.

The damage assessment results for each IOL injector models are shown as boxplot diagrams (Fig. 5). The Emerald system yielded the highest damage score, while the other two injector systems presented similar damage scores. No statistically significant difference in the total score was found between the study groups (P > 0.05). Diopters of IOLs in each group were expressed as mean ± standard deviation (SD) (shown in Supplemental Fig. 1). No statistically significant difference was found between the study groups in terms of diopters of the IOLs (P > 0.05).