The microkeratome is a type of surgical item that comes with a special oscillating blade that was created to make flaps in the cornea for ALK or Lasik surgeries. The average cornea for a human will between 500 and 600 micrometers in thickness. When it comes to the Lasik procedure, a microkeratome will make a flap in the cornea that is between 80 to 200 micrometers thick. It is this item that is actually used all over the world in order to cut into the cornea and it is used to create corneal flaps. Another thing is that this instrument is also used within DSAEK, where a thin layer is taken from the back of a cornea of a donor which will then be transplanted to the posterior cornea of the patient. This tool was created by Cesar C. Carriazo and Jose Barraquer in Colombia during the 1950s.
The main principles for this tool are to create flaps in the cornea however, attached to this tool is a suction ring. The suction ring will have 2 different uses. It is able to stick to the globe of the eye which creates a stable area for the cutting head of the microkeratome. It is also used to raise IOP to a higher level which is able to give the cornea stability.
The size of the suction ring will be what determines the size of the flap and even the size of the stabilizing hinge. The thicker the size of the suction ring and the smaller the diameter, the less that the cornea will stick out which means that there is a smaller flap created. The suction ring is often connected to a type of vacuum pump which is normally controlled by a foot pedal that allows it to be turned off and on.
There are several parts for the cutting head of the microkeratome. The disposable cutting blade is highly sharpened and it is thrown away after each patient, no matter if it is just a single eye or both eyes. The plate or head will flatten the cornea before the cutting blade is applied. The blade length that will extend past the plate and the blade clearance as well as the applanation surface are the main points that will determine the thickness of the flap.
The motor will be a gas driven turbine or electrical and this is what rapidly oscillates the blade, and this is normally between 6000 to 15000 cycles in a minute. The tool may have a second motor, or it could be a single motor which is what will run the cutting head and advance it across the cornea. This is attached the tools suction ring. However, there are model types that may have to be manually controlled in order to start moving the cutting head. The thinner and small flap size and long hinge length might be seen to be more important than the location of the hinge as it may spare nerves which will reduce incidences and even the severity of dry eye. It does not matter what type of hinge is used, most patients will often recover their sensation to the cornea within a year after surgery, however some may get this sensation back within 6 months.
Once the suction ring is positioned correctly, the suction will be activated. It is at this time that the IOP will need to be assessed because having a low IOP may cause a thin, incomplete, or poor-quality flap to be created. It is very important to have the best exposure of the eyes, which will allow there to be free movement of the tool and having a proper suction ring fixation will help as well.
Whenever there is inadequate suction it may be due to a blockage in the suction ports that could be from scarred or redundant conjunctiva or eyelashes under the suction ring. In order to avoid the chance of pseudosuction, the surgeon will need to confirm that there is actually suction by watching to see if the eye will move while the suction ring is moved and if the pupil is only slightly dilated and that the patient is not able to see the fixation light. There are methods that may be used to assess if the IOP is elevated enough which may include using a Barraquer applanator or eye palpation by the surgeon.
One thing that should be remembered about using a microkeratome is that balanced salt solutions should not be used as it may cause mineral deposits to develop in the tool and cause issues with how it works. The tool will be placed on the eye but only after the eye is checked for obstacles. When the tool is activated it will be passed over the cornea until it is stopped by the stopper which is what creates a hinge and then it will be reversed off of the cornea.
Before the tool is ever used in surgery, the microkeratome and suction are put together and inspected carefully and then they will be tested in order to make sure that they will work properly during the surgery. It is very important that the microkeratome is maintained and that the recommendations by the manufacturer are followed is one of the things that could never be stated enough.
Additionally, the surgeon will need to be aware that even if the label describes how thick the flap will be on a certain device, the actual size will be varied based on the type of tool that is used as well as pre-op thickness, pre-op astigmatism, pre-op keratometry, patient age, translation speed, and the diameter of the cornea. It is very important that a translation speed is steady which helps to ensure that there are not any irregularities within the stroma.
The microkeratome will have a long life, but it is the proper maintenance after it is bought will be very important no matter what model you pick. The maintenance has not changed too much and now the surgeons are very cautious about the type of cleaner that is being used in order to avoid DLK or diffuse lamellar keratitis. It is always recommended that the tool be sterilized between each patient and that the sterilizer is clean as well as to keep DLK instances down.