- Changes in the biomechanical properties of the cornea associated with age appear to be responsible for the arrest of keratoconus
(KC) progression. Early treatment of KC is crucial, although traditional treatments may carry risks or prove ineffective in
younger patients. Intacs intracorneal rings offer a safe and effective treatment option both for young patients and those
with later-stage KC.
Keratoconus (KC) is non-inflammatory corneal ectasia which has its onset at puberty and progresses until the third to fourth
decade of life, when it usually arrests. Recently, the varying biomechanical properties of the cornea in different age groups
have been the focus of intense KC research. Experimental ex vivo studies have shown that an age-related change in corneal collagen fibril properties may contribute to an increased stiffening
of the cornea as it ages.1,2 These findings were supported by a study I conducted, which evaluated 482 keratoconic eyes and demonstrated an inverse correlation
between age and the severity of KC (Figure 1).3
Because of the nature of the condition, one would expect that, even in cases of slower disease progression, older patients
would have more severe disease, demonstrated by, for example, higher mean Ks. In our study, however, we had a smaller number
of keratoconic eyes and less severe disease in older patients, although we currently have no explanation for this. A previous
study4 reported a negative correlation between corneal viscoelastic properties with advancing age, which could provide further
evidence of an increase in cross linkage of collagen fibrils in the cornea with age, causing it to have a stiffer and less
elastic structure. If it is indeed true that the cornea gets stiffer with age, it is also possible that KC progression may
stop, or even that KC may regress, with age.
Options for early KC treatment
The inverse correlation between age and the severity of KC we have established makes it clear how important it is to treat
young keratoconic eyes. Most young patients with keratoconus want to achieve a high quality of vision, with minimal risk,
rapid rehabilitation, minimal discomfort and pain. This is why the first line treatment of KC is usually with rigid contact
lenses, although during adolescence and peak life activity, patients may be more intolerant of these lenses. Contact lenses
also carry with them the risk of, for example, corneal warpage, allergic reaction, dry eye, and infection.
Another option for early treatment is penetrating keratoplasty, which has been associated with only limited success in younger
patients. This limited success can be attributed principally to pre-, intra- and postoperative problems, because low scleral
rigidity, increased intraoperative fibrin formation, and positive vitreous pressure complicate the surgical procedure.
The intracorneal ring implant Intacs is also indicated for KC. The purpose of Intacs segment implantation is to defer the
need for corneal transplantation and restore contact lens tolerance. The placement of Intacs generates an immediate response
that interrupts the biomechanical disease progression and a biomechanical response that allows improvement of vision over
six months. This improvement in visual acuity and refraction is accomplished by shortening the path length of the portion
of the collagen lamellae that are central to the segments. The redistribution of corneal curvature leads to a redistribution
of corneal stress, interrupting the biomechanical cycle of the KC progression, and, in some cases, even reversing the stress.
Although some studies report Intacs improves visual acuity as well as refractive and topographical findings in keratoconic
patients, the effectiveness and safety of the implant in different age groups remain unknown. To investigate further, I conducted
a study comparing the response to Intacs treatment in KC patients of different ages, assessing whether an age-related increase
in corneal "stiffness" could impact the outcome of Intacs treatment. At the one year follow-up point, the study did not find
any statistically significant differences between young, middle and older age groups in visual acuity, manifest sphere, cylinder,
mean refractive spherical equivalent (MRSE) or mean-K readings (Figure 2, Tables 1 and 2) (ANOVA, p > 0.05).5 We therefore concluded that Intacs is as safe and effective in adolescent KC patients as in other age groups.
Table 2: Change in manifest refraction (sphere and cylinder) and MRSE one year after Intacs implantation arranged by groups.
Table 1: Preoperative parameters before Intacs implantation arranged by groups.
Intacs outcomes in severe keratoconus
In a separate study, we evaluated Intacs efficiency according to different keratoconus stages.6 This retrospective, non-comparative case series reviewed 306 keratoconic eyes of 255 patients who had had Intacs segment
implantation. Patients were grouped according to the Amsler-Krumeich keratoconus classification (stage II, 155 eyes; stage
III, 83 eyes; stage IV, 68 eyes).
There was no significant difference between the three groups in the amount of change in BCVA (Figure 3), manifest spherical refraction, or manifest cylindrical refraction (p > 0.05) (Figure 4).
Postoperatively, the stage IV group demonstrated less change in uncorrected visual acuity and more improvement in mean K values
(p < 0.05, ANOVA). Six months after implantation, segment extrusions occurred in three eyes in the stage IV group: the patients
were 18, 20 and 23 years old.
Improvements in visual acuity and astigmatism after implantation, in corneas with and without scarring due to keratoconic
hydrops, have previously been reported.7 In that study, the BCVA improved to a greater degree in the scarring group than in the no-scarring group, and at the final
follow-up visit (12 months postoperatively) Intacs had prevented the need for corneal transplantation. To our knowledge, this
is the only study that suggests that patients with paracentral scarring or with corneas steeper than 57.0 D would benefit
from Intacs. As our study found that Intacs implantation was effective in eyes with severe KC, however, our results support
these earlier findings.
The first clinical results of the use of the femtosecond laser (which has demonstrated potential for high-precision micro
machining and other applications) in Intacs treatment were reported in 2003.8 There were no intraoperative complications with the femtosecond laser in our study, and although segment extrusions occurred
in three eyes during follow-up, this is less than the complication rate reported by Kanellopoulos,9 which was as high as 35%. Complications in that study included segment movement, exposure and corneal melting with mechanical
tunnel dissection. The difference in complication rates may be attributed to use of the femtosecond laser method for channel
creation and wide channel parameters.
Intacs recommended in all ages and stages
In both studies I conducted, in early and severe KC eyes, Intacs was a safe and effective treatment option. The efficacy of
the implant was not compromised by implantation in young eyes, and although segment extrusions occurred in three stage IV
eyes, the rate of complications remained low. Overall, I would recommend Intacs as a treatment whatever the age of the patient
and whatever the stage of the disease. Although early treatment is recommended, Intacs implants remain effective even in eyes
with severe KC.
1. K. Zadnik, et al. Invest. Ophthalmol. Vis. Sci. 1998 Dec;39(13):2537–2546.
2. C. Kirwan, et al. Am. J. Ophthalmol. 2006;142:990–992.
3. A. Ertan & O. Muftuoglu. Cornea 2008:27(10):1109–1113.
4. C.A. McCarty. Clin. Exp. Optom. 2002;85:91–96.
5. A. Ertan & E. Ozkilic. J. Refract. Surg. 2008;24:690–695.
6. A. Ertan & G. Kamburoglu. J. Cataract Refract. Surg. 2008;34:1521–1526.
7. T. Hellstedt, et al. J. Refract. Surg. 2005;21:236–246.
8. A. Ertan, et al. J. Cataract Refract. Surg. 2007;33:648–653.
9. K.G. Carrasquillo, et al. Cornea 2007;26(8):956–962.