Intacs or Intac Corneal Ring Segments (ICRS) are plastic semi circle segments which are inserted at a precise depth in the Cornea. They decrease the bulge and improve vision. Sometimes the vision improvement can be immediate.
The placement of intacs is very important. The older manual system or the technically advanced OCT guided intralase femtosecond laser.
Why is the OCT guided intralase placement better than manual prolate system?
Measure 10 times, Place once.
Manual pachymetry can determine thickness of the cornea only at certain chosen points. OCT or ocular coherence tomography determines the thickness over hundreds of points. This is displayed as a color coded map. OCT also determines the thinnest point on the cornea of a keratoconus patient.
Accuracy in channel creation.
Intralase is a femtosecond laser. This laser can have it action at a predetermined depth. If it is programmed to fire at 400 micron depth, it will have a uniform action at that depth. In a keratoconus cornea this accuracy is essential. If we we want to place the intacs ring segment at 4oo microns, the intralase laser ensures the entire channel is created at that depth. Manual prolate system is unable to deliver this accuracy. A lot of variables like hand pressure, angle of entry of handheld blade, direction of channel creator and resistance of cornea affect the outcome. These sources of error lead to variability in depth at start of channel and in the rest of the channel. This can lead to perforation or channel coming to the surface of the cornea,
Width of channels.
Intacs ring segment come in different size ranging fron 210 microns to 450 microns. Their thickness and size is different. Femtosecond laser can create channels of different size to ensure an optimal fit for the intacs. The manual hand held system shown on Doctors show creates only one size channels. The bigger segment would be tight whereas the thinner segments would have too much place and can move.
Prevents extrusion or spitting out.
Femtosecond laser actually makes two sets of openings. A circular one and a vertical one which is perpendicular to the circular channel. The vertical one joins the circular laser channel. This 90 degree junction prevents the intacs from coming to the surface of the cornea through the wound of entry. The prolate manual system has just one continuous channel. This curved wound of entry is a single channel. You may have heard of the dictum-‘what goes up comes down’. In this case what goes in can come out. Remember, keratoconus patients suffer from allergies and are prone to rubbing their eyes. This rubbing movement can cause the intacs to move.
Since the femtosecond channels are ideally placed at 90 % depth of the cornea, there is enough tissue above it to act as a barrier. This depth also allows nutrition tor the top of the cornea. Surgeons who cannot afford the advanced laser system use the manual system to place intacs at a depth of 75 % of the cornea. It can end up at 50 % of the depth. With little tissue above it the nutritional supply and the tectonic strength is compromised. the intacs ring segment can end up breaking through by dissolving the cornea above it.
The safety and efficacy of the intacs ring segment is highest with OCT and femtosecond lasers like intralase laser. Many published studies in peer reviewed international scientific journals have documented this. Famous TV hosts should read articles like these to educated themselves and their audience.
Rajesh Khanna, MD