Surgical Techniques in Ophthalmology: Corneal Surgery Ashok Garg, Boris Malyugin, Bojan Pajic, Jorge L Alio, Belquiz A Nassaralla, Mahipal S Sachdev, Keiki R Mehta, Roberto Pinelli, A John Kanellopoulos, Carlo F Lovisolo, Jes N Mortensen, Francisco Sánchez León, Frederic Hehn, Arun C Gulani, Quresh B Maskati
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Surgical Techniques for Corneal Reshaping (Keratoconus—KCN) and other Corneal Diseases

Intracorneal Ring Segments for KeratoconusChapter 1

Belquiz A Nassaralla,
João J Nassaralla Jr
(Brazil)
 
AN INTRODUCTION
Keratoconus is a corneal ectatic disease that is characterized by noninflammatory progressive thinning of the cornea. Since the utilization of penetrating keratoplasty and rigid contact lenses, there was no improvement for the visual rehabilitation of keratoconic patients. Recently, intracorneal ring segments have been investigated to correct ectatic corneal diseases.
The aim of implanting intracorneal ring segments is not to treat or eliminate the existing disease, rather a surgical alternative to reinforce the cornea, decrease the astigmatism and corneal abnormality and thus increase the visual acuity to acceptable limits, aiming to at least delay, if not eliminate, the need for corneal grafting.
This is a surgical treatment which involves the implantation of two semicircular micro-thin polymethylmethacrylate (PMMA) inserts of variable thickness (ranging from 0.15 mm to 0.35 mm) that are slid between the layers of the stroma on either side of the pupil, into 75% depth of the peripheral corneal stroma. The segments push out against the curvature of the cornea, flattening the peak of the cone and returning it to a more natural shape.
Since its release, intracorneal ring segment insertion for keratoconus seems to be effective with minimal complications. The additional benefit of intrastromal rings is that they can be removed or replaced if they do not carry out their function correctly, or if they become intolerable, although there are very few cases describing intolerance to these segments.
Intrastromal corneal rings are mostly for keratoconic patients of any age with an evolving condition, in whom the cornea has remained transparent, and who are intolerant to contact lenses or with sharp distortions in the corneal shape, which usually occur after transplants.
The success rate is inversely proportional to the keratoconus severity level. Thus, the earlier the surgery is performed the greater is the chance of success.
The surgery is performed in an operating room, under topical anesthesia. The procedure is painless and lasts about 10 minutes. The main possible complications include: infection, segment migration, extrusion, decentration, halos and glare.
Figures 1.1 to 1.11 show the step by step technique. Surgery was performed on the left eye of a 21 year-old male patient with bilateral stage II keratoconus. Onset began in his late teens and progression was rapid. Before surgery, manifest refraction on his left eye was -3.50 -4.25 × 150°. Best spectacle corrected visual acuity was 20/50. In this case, two PMMA segments (Cornealring, Visiontech, Belo Horizonte, MG, Brazil) with 155° of arc were implanted into two intrastromal tunnels of 5 mm of diameter (4.7 mm and 5.9 mm of internal and external diameter, respectively). A thicker (0.20 mm) segment was inserted into the more affected corneal hemisphere (temporal).2
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Figure 1.1: Visual axis marking on microscope (light reflex), not on the center of the pupil. It allows for easier centration
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Figure 1.2: Marking of 5/7 mm optical zones with a gentian violet inked instrument
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Figure 1.3: Marking of steepest meridian
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Figure 1.4: Incision making at the steepest meridian, 75% depth of local pachymetry
A 0.15 mm thick segment was used into the less affected corneal hemisphere (nasal).
Figure 1.12 shows the preoperative topography (Osbscan™, Bausch & Lomb) before surgery. At this time, keratometry readings were 53.2 × 63°/ 47.6 × 153°, and the thinnest pachymetry was 450 microns.
Figure 1.13 shows the postoperative topography (Osbscan™, Bausch & Lomb) one week after surgery. Note the significant cone flattening. Keratometry readings were 45.7 × 65°/ 41.6 × 155°, and the thinnest pachymetry was 455 microns. Manifest refraction was -1.50 -1.00 × 150°, and best spectacle corrected visual acuity had improved to 20/25.
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Figure 1.5: Creation of intrastromal pockets with Suarez spreader (depth equal to incision)
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Figure 1.6: Sequential tunnel creation using the right spatula
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Figure 1.7: Sequential tunnel creation using the left spatula
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Figure 1.8: Segment implantation with Albertazzi forceps. Segment inserted with flat side down
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Figure 1.9: Insert each segment all the way to the end of the tunnel
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Figure 1.10: Final aspect
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Figure 1.11: Therapeutic soft contact lens for 24 hours
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Figure 1.12: Preoperative topography (Osbscan™, Bausch & Lomb) before surgery
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Figure 1.13: Postoperative topography (Osbscan™, Bausch & Lomb) one week after surgery
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