Shrestha Dutta, Amity University Kolkata
Keratoconus is a continuous ectatic corneal disorder that gives rise to corneal stroma impedance and biomechanical weakening. Corneal collagen cross-connecting (CXL) is a powerful treatment to stop the growth of keratoconus. UV light of 3mW/cm2 is utilized in classic Dresden CXL for brightening and a single treatment technique needs 60 min to reach total energy of 5.4 J/cm2. Recently, scientists have created accelerated CXL conventions that trigger the techniques utilizing high-intensity radiation. Several conventions have been accounted to give practically identical outcomes to the classic Dresden CXL. Moreover, accelerated CXL has been demonstrated to oppose the growth of keratoconus in most pediatric patients.
Past research works suggest combining various techniques of CXL and photorefractive treatment performed simultaneously or in two steps, exhibited a critical improvement of keratometry readings and visual capacity. Previous research works show that photorefractive removal with halfway refractive rectification was utilized taking all things together or some portion of the cases, targeting lessening the lower as well as the higher-order variation is the main reason for corneal astigmatism. In this way, photorefractive treatment should rely on rectifying just higher-order distortions, to limit the deficiency of corneal stroma.
Assessment of patients:
All patients had a full ophthalmological assessment, including uncorrected distance visual acuity (UDVA), cycloplegic and show refractions, best spectacle-corrected distance visual acuity (BSCDVA), slit-light assessment, Goldmann applanation tonometry, and fundoscopy assessments. With the Sirius consolidated topographer and tomographer (CSO, Italy), the following conditions were assessed:
- maximal keratometry value of the anterior surface (Kapex)
- flat axis keratometric value (K1),
- steep-axis keratometric value (K2)
- corneal astigmatism
- minimum corneal thickness (ThkMin)
- curvature symmetry index front (SIf)
- keratoconus vertex front (KVf)
- Baiocchi Calossi Versaci file front (BCVf)
- root-mean-square of the absolute higher-request aberrations (HOA-RMS)
- Coma (Coma-RMS)
- Spherical abrations (SA-RMS).
Corneal topography information for topography-directed modified ablation was modified from the Placido-based topographer (Vario Topolyzer, Alcon, USA). Corneal endothelial cell density (ECD), hexagon cell rate (HEX), and cell region variation coefficient (VC) was analyzed by specular microscopy (Topcon, Japan).
Treatment procedures:
Many treatments were performed by the same specialist –YG Chen. Under effective sedation, freshly made 20 % liquor was imparted into the epithelial trephine with a width of 9.0 mm, soaked for 20 s. Then, at that point, the corneal epithelium was stripped and taken out. TG-PRK was performed utilizing the topography-guided (Topolyzer) programming of WaveLight EX500 excimer laser framework (Alcon, USA) with an optic zone of 5.0 ~ 6.0 mm. TG-PRK refers to the amendment of neither refractive circle nor cylinder, yet 0 ~ – 2.25D of measured (“estimated”) chamber which was consequently determined dependent on the Topolyzer geological outcomes.
The classic Dresden CXL utilizing bright light of 3mw/cm2 brightening is a tedious methodology, which can cause a high rate of haze and the risk of continuous corneal smoothing, particularly in synchronous combined medicines. The accelerated CXL utilizes bright light of high illumination power. As per the Bunsen-Roscoe law of photochemical impact, the higher the enlightenment, the less the exposure time. The exposure time required is extraordinarily abbreviated, which further develops the treatment effectiveness and builds patients’ consistency. Also, accelerated CXL was demonstrated to be successful and have fewer entanglements. Thus, accelerated Corneal collagen cross-connecting (CXL) has been generally utilized by most specialists for CXL combined treatment.
Conclusion:
Researches show that the critical improvement in BSCDVA, Kapex, corneal inconsistency indices, and RMS of HOA and coma, and also showed great dependability in refraction and corneal arch after synchronous TG-PRK without refractive amendment followed by accelerated CXL (30mW/cm2) in patients with mild-to-moderate keratoconus growth. The treatment convention is advantageous, efficient, viable, and safe. However, large-scale, similar, long-term preliminaries are needed to decide the ideal parameters.
Also read: Reverse optogenetics tool using zebrafish
Reference:
- Zhang, Yu, and Yueguo Chen. “Topography-Guided Corneal Surface Laser Ablation Combined with Simultaneous Accelerated Corneal Collagen Cross-Linking for Treatment of Keratoconus.” BMC Ophthalmology, vol. 21, no. 1, July 2021, p. 286. BioMed Central, doi:10.1186/s12886-021-02042-x.https://bmcophthalmol.biomedcentral.com/articles/10.1186/s12886-021-02042-x#Abs1
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