Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard mini Atlas Series Lasik_Aragawal, Jacob_2009

MISCELLANEOUS TOPICS/ 187

Figure 4.3A

Figure 4.3B

188 / LASIK

Figure 4.3C

Figures 4.3A to C: Conductive keratoplasty (Figure & Text Courtesy: Scott G Hauswirth, Elizabeth A Davis). (A) CK machine;

(B) Optical zones for CK; (C) Optipoint insertion

Conductive keratoplasty is based on radiofrequency energy. The controlled release of radiofrequency waves causes shrinkage of corneal collagen. As the treatment is

190 / LASIK

6 mm and the outermost at 8 mm with the intermediate one at 7 mm (Figure 4.3B). Spot placement is defined according to predetermined nomograms. The spots are generally given at a 7 mm zone circle followed by additional spots if needed. The number of spots varies from 8 to 32 spots. Radiofrequency energy of 350 MHz is delivered through a thin metal probe: the KeratoplastTM tip (450 × 90 microns) in the peripheral cornea at the predetermined spots. The tip is held perpendicular to the corneal surface. The profile of energy given is 350 MHz, 60% power for 0.6 seconds per spot. The tip provides a uniform cylinder of energy with the depth reaching upto 80%. Deep penetration of the tip is prevented by the Teflon-coated governor. The light touch technique started by Milne is preferred. The newer OptiPoint device (Figure 4.3C) helps to minimize overcompression and ensures correct depth of penetration, accurate placement of the probe, correct angle of approach, and correct spacing of CK spots on the radial axis. This has the potential advantage of decreasing regression as well as increasing the effect of CK.

MISCELLANEOUS TOPICS/ 191

Figure 4.4A

Figure 4.4B

Figures 4.4A and B: Conductive keratoplasty for post-cataract surgery astigmatism. (A) Preand post-CK Orbscan pictures.

192 / LASIK

Note steepening of the central cornea; (B) Agarwal nomogram for post-cataract astigmatism of a patient with + 1.0 D sph with + 1.5 D cyl at 90 degrees. In this case 8 spots at 8 mm corrects the sphere and 4 spots at 7 mm corrects the cylinder. These 4 spots are placed at 180 degrees.

CK in patients with post-LASIK astigmatism resulted in improved corneal optics and visual acuity. CK can be a viable alternative in patients for whom further laser procedures are contraindicated. Astigmatism due to incomplete flap after LASIK can be treated with CK. It has also been tried to resolve post-operative glare and halos. Post-LASIK decentered ablation, striae and topographic irregularities were also treated. Intraoperative treatment of astigmatism in patients treated with CK can be done. Flat axis is determined with automated keratometers and additional spots are given in these points in flat axis in 7 mm zone. Intraoperative treatment of astigmatism through the addition of more spots at the minus cylinder or flat axis reduced the degree of induced astigmatism. CK can also be used in astigmatism due to corneal trauma or scarring and after decentered ablation. CK has been tried in corneal ectasias like keratoconus and pellucid marginal degeneration. The aim was to move the cone to the center and improve the quality of vision. Pinelli has tried CK in pellucid marginal degeneration with

194 / LASIK

Table 4.2: Agarwal’s nomogram for post-cataract surgery astigmation

MISCELLANEOUS TOPICS/ 195

Figure 4.5: Presbyopic inlays (Figure & Text Courtesy: Jaime R Martiz)

The current presbyopic Inlays (Figure 4.5) products are designed to surgically insert a small sized lens with or without positive refractive power in the corneal stroma at a point that is exactly in front of the center of the pupil. With the Inlays implanted, the cornea becomes bifocal, hyperprolate shape or pinhole depending on the product. Currently, three different corneal inlays are being developed: the AcuFocusTM/Bausch & Lomb ACI 7000, (Irvine, California), the InvueTM intracorneal Inlay

196 / LASIK

(Biovision, Switzerland) and the PresbyLens® (ReVision Optics, Lake Forest, California). The corneal inlays are somewhat very similar to each other in diameter. All of them are under investigation and are designed to be implanted in the non-dominant eye, but the problem is biocompatibility, they got all the advantages and fewer disadvantages of other technologies. All of them can use a femtosecond laser to create the flap, tunnel or pocket to increase precision and safety.