to achieve their best-corrected vision. Eyes with corneal scarring had a similar improvement in UDVA and CDVA. Inferior steepening was reduced on topography. The dioptric power of the inferior cornea relative to the superior (I–S value) was reduced from a preoperative mean of 25.62 to 6.60 postoperatively.

A study evaluating the long-term stability of Intacs in keratoconus found that in nearly 93% of patients with documented progression of keratoconus pre-Intacs, there was no further progression of keratoconus between 1 and 5 years after Intacs implantation. Additionally, no statistically significant differences were noted in mean steep, flat, and average keratometry readings; manifest refraction spherical equivalent; and UDVA and CDVA (P > .05) between 1 and 5 years postimplantation.

One or Two Intacs Segments?

Although most surgeons implant 2 Intacs segments, the use of only 1 segment may be indicated. If the steep area is peripheral (similar to pellucid marginal degeneration), it may be preferable to place 1 segment instead of 2 segments because the keratoconic cornea has 2 optical areas of distortion within the pupil: a steep lower area and a flat upper area. For peripheral keratoconus, it is better to flatten the steep area and steepen the flat area than to flatten the entire cornea. Single-segment placement can achieve that result (Fig 4-5). When a single segment is placed, it flattens the adjacent cornea but causes steepening of the cornea 180° away—the “beanbag effect” (ie, when one sits on a beanbag, it flattens in one area and pops up in another area). This effect may yield a more physiologic improvement than would the global flattening effect from the use of double segments. Intacs treatment can also be combined with corneal collagen crosslinking (not yet FDA approved) for improved corneal strength and phakic IOL implantation to improve refractive error.

Figure 4-5 Corneal topography analysis before and after single-segment Intacs placement. The preoperative topography (lower left) shows oblique steepening, and the postoperative topography (upper left) shows contraction of a steep cone after a single-segment Intacs was placed outside the cone. The difference map (subtraction of preoperative and postoperative topography) (right) shows flattening over the cone (blue) and steepening in the overly flat area (red). The apex of the cornea

has moved more centrally. (Courtesy of Brian S. Boxer Wachler, MD.)

Bedi R, Touboul D, Pinsard L, Colin J. Refractive and topographic stability of Intacs in eyes with progressive keratoconus: five-year follow-up. J Refract Surg. 2012;28(6):392–396.

Ertan A, Karacal H, Kamburoğlu G. Refractive and topographic results of transepithelial cross-linking treatment in eyes with Intacs. Cornea. 2009;28(7):719– 723.

Sharma M, Boxer Wachler BS. Comparison of single-segment and double-segment Intacs for keratoconus and post-LASIK ectasia. Am J Ophthalmol. 2006;141(5):891–895.

Wollensak G, Spörl E, Seiler T. Riboflavin/ultraviolet-A-induced collagen crosslinking for the treatment of keratoconus. Am J Ophthalmol. 2003;135(5):620– 627.

Complications

The loss of CDVA (≥2 lines of vision) after Intacs insertion is approximately 1% at 1 year postoperatively. Adverse events (defined as events that, if left untreated, could be serious or result in permanent sequelae) occur in approximately 1% of patients. Reported adverse events include

anterior chamber perforation microbial keratitis

implant extrusion (Fig 4-6) shallow ring segment placement

corneal thinning over Intacs (Fig 4-7)

Figure 4-6 Slit-lamp images of an adverse event of Intacs placement: extrusion of the ring segment. A, Tip extrusion. B, Tip extrusion easily seen with fluorescein dye. (Courtesy of Brian S. Boxer Wachler, MD.)

Figure 4-7 Image of an adverse event of Intacs: corneal thinning over the ring segment (arrow) after excessive use of a

nonsteroidal anti-inflammatory drug. (Courtesy of Brian S. Boxer Wachler, MD.)

Ocular complications (defined as clinically significant events that do not result in permanent sequelae) have been reported in 11% of patients at 12 months postoperatively. These complications include

reduced corneal sensitivity (5.5%)

induced astigmatism between 1.00 and 2.00 D (3.7%) deep neovascularization at the incision site (1.2%) persistent epithelial defect (0.2%)

iritis/uveitis (0.2%)

Visual symptoms rated as severe and always present have been reported in approximately 14% of patients and include

difficulty with night vision (4.8%) blurred vision (2.9%)

diplopia (1.6%)

glare (1.3%) halos (1.3%)

fluctuating distance vision (1.0%) fluctuating near vision (0.3%) photophobia (0.3%)

Fine white deposits occur frequently within the lamellar ring channels after Intacs placement (Fig 4- 8). The incidence and density of the deposits increase with the thickness of the ring segment and the duration of implantation. Deposits do not seem to alter the optical performance of the ring segments or to cause corneal thinning or necrosis, although some patients are bothered by their appearance.

Figure 4-8 Clinical photograph showing grade 4 deposits around ring segments. The deposits can be graded on a scale from 0 (no deposits) to 4 (confluent deposits). These channel deposits are typically not apparent until weeks or months after surgery. Although the corneal opacities may cause cosmetic complaints, they usually do not cause other ocular problems.

(Courtesy of Addition Technology.)

Intacs achieve the best results in eyes with mild to moderate keratoconus. The goals are generally to improve vision and reduce distortions and are determined on the basis of the degree of keratoconus. For example, a patient with mild keratoconus and a corrected distance visual acuity (CDVA) of 20/30 may have the goal of improved quality of vision in glasses or soft contact lenses. However, a contact lens–intolerant patient with more advanced keratoconus and a CDVA of 20/60 may have the goal of improved ability to wear a rigid gas-permeable contact lens. For some advanced cases of keratoconus, such as eyes with keratometry values greater than 60.00 D, the likelihood of