These are the notes I took at the Birmingham support group meeting on Saturday 25th November 2006. The presentation was given by Vijay Savant, Corneal Fellow at the Eye Centre.
First used in 1997 to treat myopia minus 1 to minus 5 dioptres (D) and astigmatism 10 D. Intacs are semi-circles of plastic inserted into the cornea.
The Intacs consist of 2 semi circular arcs made from PMMA (Poly(methyl methacrylate) stitched in for easy removal.
Indications for Intacs Use
Poor functional vision with contact lenses or glasses
Contact lens intolerance
Transplant is the only option left
Must have a clear central cornea.
Not all patients are suitable, as other conditions must be taken into account (see Contraindications). Intacs is only suitable for mild cases of Keratoconus because the corneal thickness is very important.
Corneas steeper than 46 D or flatter than 40D
Corneas less than 450 micrometers thick
Corneal diameters less than 10 nanometers and those with a high-dilated pupils size
How Do Intacs Work?
Intacs basically pulls the KC bulge in, i.e. the arc length is changed from a steep pointed angle to a shallower one, more like a gentle arc. To identify where to place the intac to reduce this arc steepness topography is done to identify the steep axis.
How Is the Intac Put In Place?
Under a general anaesthetic (sometimes done using a local anaesthetic) the eye is held in place using a strong vacuum. The centre and outer edge of the cornea is marked using a special centering stamp so the surgeon can identify from the topography where the incision is to be made and the intacs inserted. Using a diamond tipped blade a small incision is made into the cornea at the desired depth. Using the centering tool used to mark the eye, a cutter is located above the incision and the blade inserted and rotated 180 degrees. This separated the corneal layer forming a tunnel for the intac to be inserted. The tool is removed and replaced with another one that is used to make the tunnel on the opposite side. The intacs are then inserted into the tunnels and the incision closed with a single stitch.
The whole process takes about 30 minutes.
Photosensitivity (1 to 1.3% of patients)
Fluctuations in vision
Foreign body sensation like something is stuck in the eye.
Vision takes time to settle, in the region of 6 to 12 months. Innitially vision can be worse, but at the healing process continues and settles, after 6 to 12 months it has usually improved. Once at least two consecutive stable topography and visual acuity readings are obtained the sight is corrected with glasses or contact lenses. Vision can be corrected sooner if the patient is willing to pay for regular prescription changes.
The intacs procedure is reversible and means should the KC progress, a graft can still be carried out although modern views are that grafts have a 10 to 15 year life span as cells from the endothelium are lost during the graft process and do not get replaced so gradually get less as time goes on which can result in a regraft.
The aim of this procedure as with any other surgical technique used to manage keratoconus is to proved a corneal surface that enables vision to be corrected easier with glasses or contact lenses.
Perforation; anterior/exterior (the incision are ruptures)
Under or over correction
Epithelial down growth
Intrasomal implants (Intacs) are a new treatment for selected patients. Initial data suggests sight is improved however there is no long term data available yet.
This procedure is available on the NHS in the hospitals that do perform this operation, however there is a wait. This is because funding has to be applied for so that the operation can be paid for out of the hospitals allocated budget. All surgeons need to be certified as being competent to perform this operation.