Pachymeter
A pachymeter is a medical device used in eye exams to determine the thickness of the cornea. It is useful in monitoring certain eye diseases and disorders that affect the thickness and constitution of the cornea, such as glaucoma. In LASIK procedures, a pachymeter is used to assess whether the patient's cornea is strong or thick enough for refractive surgery.
Contents
Corneal thickness for LASIK
The cornea must be of a certain minimum thickness for LASIK. The absolute minimum thickness is 250 microns, but most surgeons prefer to have an additional 250-275 microns, in case additional treatment is needed. Patients with larger pupils or greater refractive index may need deeper sculpting, and thus a greater corneal thickness.
How it works
A pachymeter is a handheld device that uses ultrasound to measure the thickness of your cornea. The eye is numbed with a drop first, and the ultrasound probe is placed gently on the surface of the cornea. The test does not cause pain. Best data comes from pachymeters that
Other techniques use optical pachymetry. In this case, the probe does not touch the surface of the eye.
Equipment
Glaucoma and Cornea
Glaucoma, Corneal Thickness and Eye Pressure
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Photorefractive Keratectomy, or PRK, is a type of laser eye surgery for people who suffer from nearsightedness (myopia), farsightedness(hyperopia) or astigmatism. It is similar to LASIKin that it involves using an Excimer laser to reshape the cornea to minimize or eliminate your dependence on eyeglasses or contact lenses.It is different in that unlike LASIK the eye surgeon doesn't need to use a microkeratome to make a flap, but instead is able to apply the laser directly to the surface of the cornea to achieve the desired vision correction effect. PRK is better suited for people with thin corneas or certain other corneal abnormalities where using a microkeratome might not be the best choice. Also it may be preferred for those in the United States military where PRK is the approved procedure for those in active combat and certain other positions. PRK has been approved by the FDA for myopia since 1995 and for hyperopia since 1998 and enjoys an excellent safety profile. Since it does not use a microkeratome, there is no risk of flap complications. In PRK to correct myopia, the steep cornea is made flatter by removing tissue from the center of the cornea. To correct hyperopia, the flat cornea is made steeper by removing tissue from the outer edges of the cornea. To correct astigmatism, the cornea is transformed into a more spherical shape.
Process of Photorefractive Keratectomy
Photorefractive Keratectomy involves, much like LASIK, the reshaping of the cornea. Unlike LASIK which involves removing the inner tissue of the cornea, PRK applies laser energy to change the surface of the cornea. Before surgery you will need to have a careful review of your health and eye history. Then you will need to have a refraction to measure your actual prescription. This will need to be performed with eye drops; in order to get the best measurements. The shape of the surface of your eyes will be mapped using an instrument called a corneal topographer. Finally the thickness of your cornea will be measured using an instrument called a pachymeter.
On your day of surgery, a technician will clean the area around your eyes with a hygienic but gentle cleansing pad. The technician will place a series of drops into your eyes in order to get them ready for your treatment. Some of these drops, antibiotic drops, will prevent germs from entering your eye and therefore help to prevent any possibility of infection. Other drops will be placed in your eyes to lightly numb the cornea so that you are comfortable during your treatment. After you recline on the bed-like chair under the laser, an eyelid holder called a speculum, is gently placed between your eyelids to remind you not to blink. Next the epithelium, a thin, protective layer that covers the cornea, is removed. Since you have had numbing drops placed in your eyes, this will not be uncomfortable, but will feel like a slight pressure around your eyes. The surgeon will instruct you to look at a small light during your procedure. Don't worry if you cannot stay perfectly steady-just do your best. Today's laser technology uses a tracking system which will actually follow your eye movements if you can hold pretty still during your procedure. To correct nearsightedness, farsightedness or astigmatism, your surgeon will use an Excimer laser.
Eligibility
People are best suited for Photorefractive Keratectomy are people with moderate levels of myopia or hyperopia who have corneal abnormalities that make them not best suited for LASIK. However PRK may also be used for people with high prescription levels and for active military personnel.
- Better for thin corneas
- Good for low to high levels of myopia,hyperopia and/or astigmatism
- Good for people in military service
Disadvantages
- Longer healing time
- Longer time for results
Photorefractive Keratectomy is a less used procedure due to LASIK. However, it is still the procedure used when LASIK is not the best choice due to eye irregularities. As with all laser surgery, there is always a risk and side effects like light sensitivity and halos may not go away. It is important to talk with your eye care doctor about the risks in your specific case.
