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Ophthalmology Emphasizing Corneal and Refractive Issues

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Slit Lamp Relaxing Incisions

Cornea relaxing incisions are an established technique to correct astigmatism. Transverse incisions flatten the cornea in the meridian of application and steepen 90 degrees away. The problem in the past was the need to take the patient to an operating room  to perform the surgery.

Incisions can be made at the slit lamp with a few modifications of technique which we will describe here.

The first modification is that the patient is now seated at the slit lamp. Anaesthesia is accomplished with topical drops and with the lids dried, the assistant holds the lids open instead of the lid speculum  used in the OR. The surgeon’s arm is stabilized by resting the elbow on the slit lamp table and the wrist against the chinbar of the slit lamp as seen in figure B and C.

In the OR making incisions in different locations merely requires repositioning of the hand and arm. At the slit lamp the hand and arm are now fixed and a different approach is dictated. The incision can be made at the slit lamp by grasping the knife with the fingertips and using a “bellows” action to move the knife up and down as seen in figure D. If an incision is to be placed in a location not access able to the “bellows” movement of the fingers, simply have the patient look up or down.

Of course not all patients are candidates for even minor surgery at the slit lamp. The patient must be calm and be able to hold fixation. Nonetheless most patients tolerate the shot procedure well and are amazed by the improvement of vision within a few minutes.

The operation requires one special instrument, a diamond knife which will not bump into the optics of the slit lamp. In the OR the operating microscope is much farther away from  the patient than at the slit lamp The knife needs to have an angled head and there are several models available. Duckworth and Kent have a diamond knife with an angled head and adjustable depth which can be found here (figure E). Mastel Precision has a set depth knife specifically designed for the slit lamp which can be found here. There are many other short diamond knives available on the market which will also work. In addition, a 7mm zone marker is used, coated with gentian violet and centered on the pupil as seen in figure F.

The procedure begins with topical anaesthesia and placing the head in the slit lamp, eye held open by the assistant. The diamond knife is set to 0.5mm or use a preset diamond knife without pachymetry since the cornea is almost uniformly thicker than 0.5mm in the midperiphery. After marking the cornea with a 7mm marker, the incisions are made along the steep axis (figure A). The result is shown in figure G for a patient with steep axis at 180 degrees (with the rule). The nomogram is 1mm for a 1 diopter and 2mm for a 2 diopter correction. For a larger correction I use the Canrobert procedure (or “C” procedure) which is described here. With the “C” procedure one can obtain up to 6 diopters of correction although I don’t try for more than 5 diopters due to unpredictability of the result.

The procedure is easiest along the horizontal meridian. If the steep axis is at 90 degrees, make the bottom incision and have the patient look down for the to incision. For oblique astigmatism  a useful technique is to place the plus cylinder correction in the phoropter and use it as a guide to the proper axis.

  

The Blue Line Incision and Refractive Phacoemulsification, Slack Inc., published 2000, Kurt A. Buzard, M.D., Miles H. Friedlander, M.D., Jean-Luc Febrarro, M.D.

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