Gautam Chaudhary

In vivo femtosecond laser subsurface scleral treatment in rabbit eyes.

The progression of glaucoma can be reduced or delayed by reducing intraocular pressure (IOP). The properties of femtosecond laser surgery, such as markedly reduced collateral tissue damage, coupled with the ability to achieve isolated subsurface surgical effects in the sclera, make this technology a promising candidate in glaucoma management. In this pilot study we demonstrate the in vivo creation of partial thickness subsurface drainage channels with the femtosecond laser in the sclera of rabbit eyes in order to increase aqueous humor (AH) outflow.

3D finite element model of aqueous outflow to predict the effect of femtosecond laser created partial thickness drainage channels

Partial thickness drainage channels can be created with femtosecond lasers in the translucent sclera for the potential treatment of glaucoma. We present a 3D finite element model (FEM) that can predict the effect of these channels on aqueous humor (AH) outflow and intraocular pressure (IOP).

Aqueous humor outflow effects of partial thickness channel created by a femtosecond laser in ex vivo human eyes

The reduced outflow rate caused by the increased resistance through trabecular meshwork (TM) has been thought to be the main reason for elevated intraocular pressure (IOP). It has been demonstrated that femtosecond laser pulses tuned to 1.7 μm wavelength can create the partial thickness channel in the sclera in ex vivo human eyes [1] and aqueous outflow can be increased by these channels in porcine eyes [2]. It was also shown that the outflow rate is reduced over time in ex vivo human eyes [3]. Therefore, the control experiment without laser treatment at the same condition was conducted and showed that outflow was reduced by 1.5 ± 0.8 μl/min at 15mmHg and 1.8 ± 1.0 μl/min at 25mmHg. However, the outflow rate increased by 0.26 μl/min at 15mmHg and 0.15 μl/min at 25mmHg after the partial thickness channel was created, meaning the amount of increased outflow rate might be more than measured considering the outflow reduction in control experiment. We suggest that the femtosecond laser created partial thickness channel can increase the outflow rate and delay the progression of glaucoma.

Imaging subsurface photodisruption in human sclera with FD-OCT

Photodisruption of femtosecond laser at 1700nm wavelength has been demonstrated as a potential subsurface surgical method that can be used in trabeculectomy for glaucoma treatment without causing failure due to scarring at the level of conjunctiva and underlying tissue [1, 2]. In this study, Fourier domain optical coherence tomography (FD-OCT) technology is used to demonstrate high speed non-invasive imaging of high precision photodisruption in human sclera. Photodisruption cavities of different size in human sclera can reveal itself in its 3D FDOCT image. Transclera channel cut from back to surface and partial transclera channel are easily identified in 3D OCT image. The whole 3D data set acquired with high speed frequency domain OCT system permits further quantitative analysis of subsurface phtodisruption incisions. The preliminary results indicate that high speed frequency domain OCT system is a good candidate for imaging subsurface photodisruption with femtosecond laser and its 3D image may provide good guidance during surgical procedures when it is integrated with laser ablation system.

Investigation and visualization of scleral channels created with femtosecond laser in enucleated human eyes using 3D optical coherence tomography images

We used optical coherence tomography (OCT) for non-invasive imaging of the anterior segment of the eye for investigating partial-thickness scleral channels created with a femtosecond laser. Glaucoma is associated with elevated intraocular pressure (IOP) due to reduced outflow facility in the eye. A partial-thickness aqueous humor (AH) drainage channel in the sclera was created with 1.7-&mgr;m wavelength femtosecond laser pulses to reduce IOP by increasing the outflow facility, as a solution to retard the progression of glaucoma. It is hypothesized that the precise dimensions and predetermined location of the channel would provide a controlled increase of the outflow rate resulting in IOP reduction. Therefore, it is significant to create the channel at the exact location with predefined dimensions. The aim of this research has two aspects. First, as the drainage channel is subsurface, it is a challenging task to determine its precise location, shape and dimensions, and it becomes very important to investigate the channel attributes after the laser treatment without disturbing the internal anterior structures. Second, to provide a non-invasive, image-based verification that extremely accurate and non-scarring AH drainage channel can be created with femtosecond laser. Partial-thickness scleral channels created in five human cadaver eyes were investigated non-invasively with a 1310-nm time-domain OCT imaging system. Three-dimensional (3D) OCT image stacks of the triangular cornea-sclera junction, also known as anterior chamber angle, were acquired for image-based analysis and visualization. The volumetric cutting-plane approach allowed reconstruction of images at any cross-sectional position in the entire 3D volume of tissue, making it a valuable tool for exploring and evaluating the location, shape and dimension of the channel from all directions. As a two-dimensional image-based methodology, an image-processing pipeline was implemented to enhance the channel features to augment the analysis. In conclusion, we successfully demonstrate that our image-based visualization tool is appropriate for effective investigation and evaluation of femtosecond laser-created, partial-thickness aqueous humor drainage channels in the sclera.

RZSweep: a new hardware-assisted volume-rendering technique for regular datasets

A long-standing challenge in the field of volume rendering is to obtain high quality images in near real-time. This is particularly important for scientific datasets where highly precise results are required to ensure accurate data interpretation. We present RZSweep as a new hardware-assisted technique for volume rendering of regular datasets based on the plane-sweep paradigm. Although some research has been done in the past for irregular datasets, we present the first attempt to explore the capabilities of the plane sweep paradigm for regular datasets. RZSweep is an exact, object order, direct volume rendering (DVR), back-to-front projection algorithm wherein a plane sweeps through the volume in depth order, projecting all the data elements within the user specified threshold onto the image plane. The algorithm uses a hardware rendering pipeline to composite the final image. The space complexity of the algorithm is bound to the number of vertices in the largest diagonal plane of the dataset. A prototype of the algorithm renders a dataset of size 256/sup 3/ in near real-time of 0.77 seconds on a single off-the-shelf commodity hardware PC. Every data element within the specified threshold contributes to the final image in its correct spatial order that is guaranteed by the use of a heap.