January 2, 2020 | Author: Admin
Keratoconus is the disorder of the cornea of the eye. Keratoconus is a progressive condition that is characterized by thinning of the cornea. Thinning of cornea distorts its shape leading to various vision disorder symptoms. Common symptoms experienced by patients suffering from Keratoconus include double vision, astigmatism, light sensitivity, blurred vision, and reduced vision. Although in most cases the disease does not cause complete loss of vision, the vision problems significantly impact the quality of life.
In the initial phase of the disease, the patient may be advised to wear glasses and a soft contact lens. However, as the disease progress and corneal thinning increases, various other treatment options are advised. The treatment for keratoconus includes corneal crosslinking, Custom soft contact lenses, Topography-guided conductive keratoplasty, Prosthetic lenses, intracorneal ring segments, contact lenses, and corneal transplant.
Corneal cross-linking is an effective method to stop the progression of Keratoconus. Various research studies have indicated the efficacy of corneal cross-linking in the management of keratoconus.
Efficacy of collagen cross-linking (CXL) in one year after treatment for keratoconus compared to no treatment by summarizing randomized controlled trials (RCTs) using a systematic review was evaluated. Five RCTs involving 289 eyes were included in the systematic review. It was concluded that corneal cross-linking is an effective treatment in preventing the progression of keratoconus for one year under certain conditions.
Another study analyzes the result and difference of treatment in the cornea with four different thicknesses when treated with UVA/riboflavin corneal collagen cross-linking in patients with progressive keratoconus. Eyes were grouped based on corneal thickness. These include eyes with corneal thickness less than 400 µm, 400-450 µm, 450-500 µm, and more than 500 µm. Various endpoints related to visual acuity, endothelial cell density, corneal topography, and TCT were evaluated at baseline, 6-months, and 12-months. At 6-months and 12-months, the visual acuity improved in all the patients. Increase of TCT along with the reduction in the change of maximum keratometry. It was concluded that corneal cross-linking is effective in halting the progression of keratoconus. Further, eyes with an advanced stage of keratoconus have a more positive impact due to treatment.
A cohort study was done to identify preoperative parameters that may predict flattening of the Keratoconic cornea after collagen crosslinking (CXL). The study found that the only risk factor for flattening rate was the preoperative maximum keratometry (K) reading of more than 54.00 D. A significant flattening occurred in more than 50% of the cases with K reading more than 54.00 D. The study further indicated that other parameters such as diagnosis, age, corneal shape factors, and sex does not have any statistically significant impact on corneal flattening after corneal cross-linking.
Intracorneal ring segments are implanted to change the refractive power of the corneal tissue. It is made of synthetic material and is used in the treatment of keratoconus.
A retrospective study was done to evaluate long-term results and stability of intracorneal ring segment (Intacs) implantation for keratoconus correction. The study comprises 13 eyes which were evaluated at 6, 12, 24 and 36 months in all the eyes and for 48 months in 6 eyes. It was concluded that the intracorneal ring segments increased the best spectacle-corrected visual acuity and decrease inferior-superior symmetry with up to 36 months of stability. Although at 6 months there was a decrease in K-value, further increase after 36 months of surgery was recorded.
Keratoconus includes the progression of the disease, corneal instability as well as distorted corneal shapes. Corneal cross-linking, as various studies indicate, prevents or slows the progression of keratoconus while intracorneal ring segments reshape the cornea. Thus, it is prudent to combine both techniques in the comprehensive management of keratoconus. It is concluded by various studies that performing these two surgeries for keratoconus management is effective. However, researchers differ in the sequence in which both surgeries are done. At least a study indicates that performing the two surgeries on a single day does not have any negative impact on the outcome but may delay the healing and recovery in visual acuity.
Some researchers point that there is no or very little effect on the sequence with which both surgeries are done. Other studies conclude that there may be an effect based on which surgery is performed first. In another study, it was shown that the effect of femtosecond reduces when corneal crosslinking was done before intracorneal ring segments.
Sometimes, both surgeries are done when one surgery is not effective to halt the progression of the disease. Intracorneal ring segments may not be able to prevent the progression of keratoconus in the patient of age less than 20 years with aggressive keratoconus. In such cases, corneal cross-linking may also be required. The time gap between both the surgeries maybe 6 months or more.
A prospective randomized clinical trial was done to assess the outcomes of corneal crosslinking (CXL) and intracorneal ring segments (ICRS) (Intacs) used adjunctively. Patients were divided into two groups. In the first group, ICRS first, immediately followed by Corneal cross-linking while in the second group, corneal cross-linking was done 3 months after ICRS. It was concluded that there was no increased risk in performing both the procedures adjunctively and a substantial improvement in corneal topography was recorded.
Although various studies support the combined effects of both these procedures there is no consensus as to how to ideally combine them. The ophthalmologists should combine both these surgeries to the patients that require them. A combination of these surgeries is effective in progressive keratoconus.
Kobashi H, Rong SS. Corneal Collagen Cross-Linking for Keratoconus: Systematic Review. Biomed Res Int. 2017
Han Y, et al. Thinner corneas appear to have more striking effects of corneal collagen cross-linking in patients with progressive keratoconus. J Ophthalmol. 2017:6490915
Koller T, et al. Flattening of the cornea after collagen crosslinking for keratoconus. J Cataract Refract Surg. 2011; 37: 1488–92
Alió JL, Shabayek MH, Artola A. Intracorneal ring segments for keratoconus correction: long-term follow-up. J Cataract Refract Surg. 2006 Jun;32(6):978-85.
Hersh PS, Issa R, Greenstein SA. Corneal crosslinking and intracorneal ring segments for keratoconus: A randomized study of concurrent versus sequential surgery. J Cataract Refract Surg. 2019 Jun;45(6):830-839
Avni-Zauberman N, Rootman DS. Cross-linking and intracorneal ring segments —review of the literature. Eye Contact Lens. 2014;40:365–70.