FEMTO LDV

The handpiece has an observation window (top) and an applanation window (below). The surgeon looks thru the 2 windows (with the excimer laser's microscope set to minimum magnification). He sees the patient's pupils and centers on it *) visually while applanating. You can make slight adjustments while applanating and before applying suction. As soon as suction is engaged, the handpiece is fixed on the cornea and cannot be moved any longer relative to the eye. For the centering process, you make the patient fixate on the excimer's fixation light.
 
*) note: Many surgeons do not center the ablation profile on the pupil center because the visual axis may not go through the center of the pupil. Also, cyclorotation has to be borne in mind. These are issues  amounting to a few tenths of a mm intentional decentration of the ablation. If you have a sufficiently large flap, you do not have to worry that much about the positioning of the flap as long as it leaves enough space to center the ablation where you need it. The LDV has an important feature that helps you in this respect: IT PROVIDES FOR THE LARGEST FLAP SIZES CURRENTLY AVAILABLE (currently 10 mm; we will soon have even a 10.5mm suction ring).
 
When centering the handpiece, you should make sure that the circle formed by the applanation window and the (larger) circle of the observation window are concentrical with the pupil. If you cannot get them concentrical, you should turn and twist the patient's head into a suitable position; not the handpiece. Be careful not to tilt the handpiece as this may lead to flaps that are not circular or may have a poorly defined edge.

First hold the LDV handpiece in the proper position just outside your field of view while looking through the microscope at the eye.  Center the eye in your field of view while the patient is looking directly at the fixation light of the excimer.  Then move the handpiece over the eye, keeping it level, and hover about 1” above the eye centering on the pupil.  Ask the patient to acknowledge that they are still looking directly at the fixation light through the windows of the handpiece.  Lower down onto the eye and push to get at least 75% of the applanation window in contact with the cornea, then apply vacuum immediately, before the patient has a chance to induce Bell’s phenomenon from an attempt to shut their eye.  If done correctly, the pupil will be well centered.

The glass window in the hand piece just applanates the cornea. Nothing moves over the cornea. The laser optics moves behind the glass. This is one of the major advantages over a mechanical Microkeratome: nothing scratching over the epithelium, and no pushing on the tissue causing uneven cutting depth.

LDV suction rings are based on the same construction principles as those for the AMADEUS’® microkeratome. However, inner and outer dimensions differ. Currently, there are four types of LDV suction rings available, for nominal flap diameters of 8.5mm, 9.0 mm, 9.5mm, and 10.0mm. These suction rings all have the same outer diameter of approximately 20mm. The two brackets of the lid speculum must therefore be at least 20mm apart so that the suction ring can be inserted between them. This may pose a limitation on extremely small palpebral fissures. However, we have only rarely run into this problem so far.

We have not had any requests for smaller flaps; but custom rings can be made upon request. Most surgeons seem to like the large flap sizes as they give you more room for the optical zone; and because with a large flap, centration of the flap is not a critical issue.

Corneal curvature (i.e. k-value) has only a minor influence on flap diameter. Between 40 D and 48D, the effect on flap diameter is only a few tenths of a millimeter. Therefore, it is recommended to select ring size depending on desired flap diameter, without adjustment based on k-value.

On a pronouncedly oblate cornea, it may be difficult to achieve a sufficiently large applanated area (the applanated area should be at least 75% of the total area visible through the suction ring). If you cannot ablate the cornea sufficiently, use a smaller suction ring (even if this sounds counter-intuitive).

For extreme k-values only (k>48D or k<38D), you may apply the following considerations: With the AMADEUS or any other mechanical microkeratome, if you have a very steep cornea you are told to use the next smaller suction ring to achieve the desired flap diameter (on a very flat cornea you should use the next larger suction ring). With the LDV it is exactly opposite:  if you have a very steep cornea you should use the next larger suction ring to achieve the desired flap diameter. (on a very flat cornea you should use the next smaller suction ring.)
This is because on the AMADEUS, the cornea protrudes up through the suction ring and the blade then cuts it off.  With a steeper cornea, more cornea will stick up through the ring so the flap will end up larger than it would on a normal cornea.  On the LDV, the cornea is flattened against the applanation window and the laser passes below it to make the cut.  A steep cornea will turn down away from the applanation window more abruptly than a normal cornea, so the laser will pass out of the cornea closer to the edge of the applanation, making a smaller effective flap diameter  (and vice versa with a very flat cornea).

Currently two kinds of InterShield spacers are available, for 140 microns flap thickness and for 110 microns.

We are currently working on a 80-90 micron flap thickness. Initial tests look promising. We hope to have this option (i.e.  a different InterShield spacer) ready in the near future.

Yes, we recommend that a speculum always be used. It is not practical to try and insert the suction ring into the lid fissure without a speculum, as the suction ring  must be attached to the handpiece prior to inserting. You can find a selection of lid specula at medcompare. A wire speculum (e.g. Seibel-type or Liebermann-type) has the advantage that it offers more space to accommodate the suction ring. However, cilia can get in the way. Therefore, some surgeons prefer a speculum with blades (e.g. Barraquer or Castroviejo type). Generally speaking, use what you are familiar and comfortable with.

For a specific recommendation, try the ASICO AE-1038N Nordan Olive Tip Speculum: 

The FEMTO LDV is currently not equipped to prepare tunnel incisions nor any other corneal incisions that require moving the laser spot up and down (in the z direction) in the cornea. The current FEMTO LDV cuts horizontally only, parallel to the applanation plane (x-y plane).  A future extension of the FEMTO LDV will however make this and other corneal surgery applications possible. Please check with us if you have a need for this kind of femtolaser application.

Suction breaks occur rarely with the FEMTO LDV.  Suction is generated by a computer controlled vacuum system which keeps suction at a constant level during the entire procedure.

Suction breaks may happen due to sudden and forceful head or eye movements by the patient. In such an event, the laser process is interrupted automatically. To remedy the situation, re-apply the handpiece , making sure positioning is exactly the same as in the first attempt; then repeat the cut.