The cornea is the clear window to the eye and is the eye’s most powerful refractive (or light bending) component. For the best visual acuity to occur, the cornea must remain clear and also present a spherical surface to the oncoming rays of light. Unfortunately, not every cornea is spherical with a surface similar to that of a basketball. Rather, some corneas are astigmatic and have a configuration comparable (in the extreme) to that of a football sliced longitudinally across the length of the ball. Astigmatism can arise after corneal transplant surgery. Even if the continuous suture has been adjusted post-operatively, once the suture has been removed, astigmatism can return.
A spherical or non-astigmatic corneal surface bends all rays of light as they strike the front of the eye to focus on the retina.
If an astigmatic cornea is present, perpendicular planes of light will be focused differently by the cornea. Only one plane of light will strike the retina while the other perpendicular plane will be focused either in front or behind the retina. This occurs in the astigmatic cornea because it has two different curves: a flatter or weaker curve and a steeper or stronger curve, analogous to the two curves of a football: the steeper curve across the laces vs. the more gentle (flatter) curve from end to end. The objective of corneal astigmatic surgery is to transform a football configuration into the curves of a basketball. The Arcitome is particularly effective in treating astigmatism following corneal transplant surgery.
The Nidek OPD Wavefront Scan is used to analyze the level of corneal astigmatism. This device projects a series of concentric rings on the cornea yielding a large series of data points which are converted into a topographic map.
The Nidek OPD Map below shows a cornea with astigmatism in a bow tie configuration at an oblique axis.
To correct the astigmatic cornea, relaxing incisions are made across the steepest axis of the cornea, i.e., across that area of the cornea showing the bow tie configuration.
Once this has been accomplished, the perpendicular planes of light should jointly focus on the retina, providing no other refractive component is present. Also, it has been demonstrated that the most effective incisions should be curvilinear or arcuate.
The Arcitome, state-of-the-art instrumentation, is used to make extremely accurate arcuate incisions. The Arcitome has two diamond blades and each blade can be adjusted for depth, degrees of arc, and radius of curvature.
Components of the Arcitome System.
Various adjustments can be made to the Arcitome to achieve an excellent post-operative result. The diamond blades are incorporated into an arcuate mechanism that allow two very precise inicisional arcs to be made in the cornea.
Arcitome is adjusted using the parameters of the nomogram to treat astigmatism following corneal transplant surgery. A slightly different nomogram is used for astigmatism not associated with penetrating keratoplasty, although another option is this instance is the use of the excimer laser.
The corneal thickness is determined using the Pachymetry Map mode of the Pentacam.
The measuring technology of the BladeScan is used to set the depth of the Arcitome. Dr. Rubman designed the integration of the Arcitome with the BladeScan and has the only unit in the world capable of performing these measurements.
All the measurements for Arcitome surgery are determined in advance and the instrument is set prior to the patient entering the operating room. As a result, the procedure takes a minimum amount of time. After the cornea has been marked with the 360 degree ruler and the steepest axis is confirmed with the Ring of Light, the Arcitome is placed on the anesthetized eye, the diamond blades activated and the arcuate incisions performed.
Dr. Rubman was the first surgeon to acquire and use the Arcitome in the NYC Metro area.