Simulador Cornealring




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The keratometry data to be supplied to the program should be, preferentially, the ones provided by the simulated keratometry “Sim K” of the axial topographical map in diopters (D).

    When the topographer instead of supplying the “Sim K”, just supplies K1 and K2 in the diameters of 3, 5 and 7 mm , we should choose the 3 mm one because it is the one the most resembles the simulated keratometry.

    The topographical map is the main tool in the determination of the surgical strategy. This way if this exam is not properly done it must be repeated until it is appropriate to be evaluated. In case this is overruled, there is a very big risk to determine inadequate Ring Segments for the case.

    The manual keratometry may be of great use, in case the map is not reliable.

    Patients bearing physical or mental deficiencies, that may create difficulties to get a good topographical map, induce the use of inadequate and mispositioned segments.

The pachymetric value to be introduced in this software is that determined in the exact site where you will make the incision. The software will calculate 75% of this value, and this must be the diamond blade calibration.

    It is important to evaluate too the pachymetry of the entire corneal area through where the segment will be implanted. This may be done through pachymetric maps obtained from equipments such as Pentacan or Orbscan, or even using a ultrasonic pachymeter that should search the whole 5mm diameter zone. The pachymetry along the implantation zone should be at least the double of the segment thickness in order to supply enough stroma to involve it, avoiding histologycal and metabolic alterations that may jeopardize the surgery results. As an example, a cornea that is 400 micrometers thick may accept segments UP TO 200 micrometers. If the software calculates, for this exemplified case, a segment of 250 micra, we should alter the planning, using a segment of 200 micra. Certainly, the corneal flattening obtained will be a little lesser than expected,  nevertheless, it is better a undercorrection, than a suffering cornea.

This software requires information about how the ectasic area is distributed in the cornea. For that, we use the steepest meridian indicated on the topography (“Sim K” of the axial map) as reference to split the cornea into two hemispheres. Then, you must observe if the ectasic area is equally distributed in both hemispheres or if this area is concentrated in just one.

    The best way to analyse the keratoconus morphology and it’s distribution in relation to the steepest corneal meridian, is to use the “Normalized Scale”.

This way, we created the following classification for the:  Ectasic Area Distribution:

Very asymmetric type: Almost the totality of the ectasic area (at least 75%) is located in one hemisphere and a small portion is placed in the other.

Moderately asymmetric type: 2/3 of the ectasic area is in one corneal hemisphere and 1/3 is in the other.

Symmetric type: The corneal steepest meridian splits the ectasic area into equal part (half by half).

We should select the subjective refraction instead of the one supplied by the auto-refraction. However, we should test the dioptric values supplied by the latter, specially in cases where the refractional exam was difficult or the patient could not determine which was the best lens. This generates an inaccurate result, what is relatively frequent in advanced keratoconus cases.

   We use the dynamic refraction instead of the static, because the pupil dilation exposes the peripheral aberrations and alters the refractional power of the eye. We should be careful in cases resulting in high myopia, higher than should be expected for a certain eye, due to the possibility to be facing an accommodation spasm. In these cases a refraction under cycloplegia is required.

Dear user: now, the Cornealring On-Line Nomogram help us to evaluate if a specific eye has or hasn’t a good Indication for the ring surgery.

This new tool is the SATISFACTOMETER !

The SATISFACTOMETER evaluates if the eye features are favorable to this kind of surgery.

Thus, this software evaluates probability of the patient becomes satisfied with the result.
The SATISFACTOMETER shows the result using Faces Images ranging from happy to angry, depending if the evaluated variable is favorable or not to obtain a good result. So, we have:

Satisfied patient.
Indifferent patient
Dissatisfied patient

The variables assessed are: K max, BSCVA, Astig value, Astig axis and Astig Coer

K max (steepest meridian): The best results are achieved when the “K Max” does not exceed 60D. Dissatisfaction can also occur if the cornea is too flat, because we know that the ring will produce an even greater flattening, which may impair vision quality.

BSCVA (Best Spectacle Corrected Visual Acuity): The goal of surgery is to improve the vision with glasses (Spectacles) or improve the fitting with contact lenses. So, the ring surgery is not indicated for eyes with good vision with glasses.
Also, an extremely low corrected vision indicates the existence of an important corneal deformation. In these cases, the probability of a bad result is real.

Astig value (Astigmatism Value): The main mechanism which the ring improves the vision is through the correction of the astigmatism. Therefore, there must be a significant astigmatism to be corrected.
On the other hand, an extremely high astigmatism indicates the existence of an important corneal deformation. In these cases, the probability of a bad result is real.

Astig axis (astigmatism axis): The steepest meridian of the cornea in eyes with keratoconus is usually oblique, positioning from superior-temporal to inferior-nasal. The absence of this typical feature may indicate that the topography is not reliable or that the corneal deformation is too important (out of therapeutic possibility for ring surgery).

Astig Coer (coherence between the axis of the refractional astigmatism and the axis of the corneal astigmatism): The astigmatic axis of refraction should be close to the  flattest meridian of the cornea. The absence of this typical feature may indicate that the topography or refraction is not reliable or that the corneal deformation is too important (out of therapeutic possibility for ring surgery).