A corneal pachymeter measures the thickness of the cornea using lasers, light waves, or ultrasound. It is used to detect and monitor eye conditions, adjust eye pressure readings, evaluate the effectiveness of treatments, and determine if a patient has enough corneal material for LASIK surgery.
A corneal pachymeter is a scientific instrument used for measuring the thickness of the cornea, the transparent window-like tissue at the front of the eye. This process, called pachymetry, uses lasers, light waves, or ultrasound to determine the distance in micrometers between the front and back surfaces of the cornea. Once the device measures corneal thickness, the pachymeter displays the number of micrometers or a corneal waveform (CWF) to the experimenter. Ophthalmologists use pachymetry measurements to detect, evaluate, and monitor a variety of eye conditions. Additionally, refractive surgeons routinely use a pachymeter in the preoperative evaluation of patients with laser-assisted keratomileusis in situ (LASIK) and in making limbal relaxation incisions (LRI).
Corneal thickness measurement with a pachymeter provides critical information in the management of glaucoma, a degenerative disease of the optic nerve associated with elevated ocular pressures. Studies show that traditional methods of measuring eye pressure underestimate eye pressure in patients with abnormally thin corneas. Patients with thin corneas and glaucoma may be at increased risk of glaucoma damage, due to the underestimation of eye pressure that occurs. On the other hand, evaluation of patients with thicker-than-normal corneas may give elevated eye pressure readings, even though the actual ocular pressures may be normal. There are several methods for adjusting the measured eye pressure to account for inaccuracies due to changes in corneal thickness.
Diseases affecting the cornea can cause distention and expansion of the corneal thickness. For example, Fuch’s corneal dystrophy is a progressive disease that destroys the endothelial cells that line the inner cornea and generally remove fluid from the cornea. Without normal endothelial cell function, the cornea eventually becomes cloudy, with pachymetry readings above 600 micrometers. An ophthalmologist will use a pachymeter to track corneal thickness and evaluate the effectiveness of his treatments.
LASIK is a procedure that alters the shape of the cornea to change the way the eye focuses light. Ultraviolet laser light smooths out the cornea, flattening areas that are too steep. When a patient undergoes LASIK, the laser thins the cornea by a fixed amount for each diopter of power it corrects. Ophthalmologists use a pachymeter before surgery to determine if a patient has enough corneal material to allow for full treatment without making the cornea too thin. Corneal ectasia, or swelling, can occur after surgery if the cornea becomes too thin, producing an uneven corneal surface and distorting vision.
If you have astigmatism, ophthalmologists can cut the cornea in the steep areas to allow the profile to flatten out in that area. These incisions are called limbal relaxing incisions. The surgeon will measure the peripheral corneal thickness using a pachymeter before setting the depth of an adjustable diamond blade, which he uses to create the incisions. Ideally, the depth of the incision should be approximately 90% of the total thickness in the incision area. Pachymetry helps the surgeon avoid a perforation through the entire cornea.
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