Abstract
Purpose :
Despite the clinical advantages of deep anterior lamellar keratoplasty (DALK), adoption is limited because it is technically difficult to accurately place a needle to the appropriate depth in the deep stroma of the cornea to perform the big bubble technique. This study tested the hypothesis that penetration force as a function of tissue depth can localize a needle in rabbit corneas. These results have applications in needle guidance for manual and robotic DALK procedures.
Methods :
Mature rabbit eyes (N=5, Pel-Freez Biologicals) were collected in phosphate buffered saline (PBS) and shipped on wet ice. Prior to the study, the eyes were injected with PBS to an intraocular pressure of 20 mmHg and centered under an OCT imager. A 25-gauge needle attached to a force sensor (GS0-1k, Transducer Techniques) was mounted on a linear stage above the eye at 30-degrees from the horizonal. The needle was visualized with OCT and inserted into each eye at a rate of 0.25 mm/s. A new needle was used for each cornea, and the insertion force was recorded at a rate of 100 samples/s. Following the experiment, the perpendicular distance from the needle tip to the endothelium was measured from the OCT images and normalized as a percentage of cornea thickness. All eyes were one day postmortem at testing.
Results :
A representative plot of the insertion force as a function of distance to the endothelium for a single eye is shown in Figure 1a. All eyes had similar force profiles with four distinct maxima (labelled as 1, 2, 3, 4). The average and standard deviation of force was 0.33±0.19N, 0.32±0.13N, 0.41±0.13N, and 0.55±0.09N respectively. The average and standard deviation of distance from the needle tip to the endothelium as a percentage of cornea thickness was 90.58±5.43%, 85.24±5.99%, 56.33±10.85%, and 17.52±7.88% respectively. The average corneal thickness was 753±33.4µm. Corresponding OCT images of the needle at each maximum are shown in Figure 1b-e.
Conclusions :
The insertion force of a 25G needle into rabbit cornea varies as a function of distance to the endothelium. Local maximum corresponding to distinct depths were observed for each eye. Before insertion force can be used to guide DALK procedures, additional studies are needed with human eyes which may have a different insertion force profile.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.