4.5.3Step 3: Discussion Step

Patient’s age is 33 years, in which KC is most likely to be stable.

Regarding the right eye: The UCVA and BSCVA are poor although the refractive error is apparently not high! This is a very important issue; the manifest refraction is not necessarily the full refraction of the patient, it represents the refraction that gives the best visual acuity but still the eye has bigger refractive error adding which will not improve the visual acuity any more. This patient indeed has immeasurable refractive error because of the much skewed scissors and the blurred image on skiascopy due to stress lines. The mentioned refraction of the patient was on trial by applying the topographical astigmatism and identifying the axis by the fan and the slit tests. Therefore, it is only the manifest refractive error that determines the management, but in some cases it may be tricky. Stress lines, immeasurable refractive error, poor UCVA and BSCVA, very high K-readings, and thin cornea are all indicators of advanced KC, hence the indication for DALK.

Regarding the left eye: Since the cornea is clear, the refractive error is measurable, BSCVA is acceptable

although the UCVA is poor, the K-readings are moderate and corneal thickness is > 450 m, both ICRs and CXL with PRK are suitable and less invasive than the DALK.

DALK was the choice for the right eye and corneal ring implantation was the choice for the left eye.

Let’s discuss the option of ICRs for the left eye. Because the cone is paracentral and the topographi-

cal pattern is PLK, there are two concepts in this regard:

1. The cone apex: When the cone apex lies on the passage of the ring, the ring might form a barrier against the action because it is within the field of action as previously mentioned.

2.The thinnest location: When the thinnest location happens on the passage of the ring, it carries the risk of penetration during tunnel creation.

The location of the cone is determined on the eleva-

tion maps and not on the curvature map. Figures 4.5.13 and 4.5.14 show the relationship between the cone and the implanted ring. The ring was implanted at the 6 mm circle. As seen in these figures, the cone is still internal to the implanted ring; therefore, there is no interference between the cone apex and the ring.

Figure 4.5.15 shows the relationship between the thinnest location and the implanted ring. As seen in this figure, the thinnest location is internal to the passage of the ring. In spite of this fact, there is no guarantee of prevention of perforation during creation of the tunnel especially if this is to be done by femtosecond. Therefore, it is strongly recommended to study all the proposed passage and take 80% of the thinnest part in this passage as a level to create the tunnel.

Figure 4.5.16 shows the anterior sagittal curvature map nearly 6 months after the operation. Figure 4.5.17 is the difference map between the preoperative and postoperative curvature maps. Note the significant improvement in the shape, K-readings, maximal K-reading (white arrows), and the amount of astigmatism (red arrows).

Six months after the left eye operation, the patient’s MR was (Table 4.5.4):

The improvement in both corneal topography and clinical refraction can be referred to the following reasons:

1.The patient is still young.

2.The cornea is clear with no stress lines.

3.The refractive error is not high (<−5 dpt).

4.The k-readings are not high (K-max < 55 dpt).

5.Corneal thickness is still good (thinnest location > 400 m).

6. The topographical pattern is type 5 in the author’s classification (PLK with straight central axes).