الفهرس 
CorneaOnly 14 pages are availabe for public view
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Abstract
SUMMARY Keratoconus (KC) is a bilateral and asymmetric progressive corneal disorder that affects the shape and structure of the cornea. The characteristic corneal thinning and irregular astigmatism in patients with KC severely impacts the final retinal image quality of the eye by higher-order ocular aberrations, making difficult its correction with spectacles or contact lenses. Intrastromal corneal ring segment (ICRS) are small devices made of synthetic material, which are implanted within the corneal stroma through a femtosecond laser made channel according to a patient-oriented strategy and empirical nomograms. It aims to induce a geometric change in central corneal curvature, thus, reducing the refractive error and the mean keratometry. ICRS is a well-tolerated and effective treatment, and increasingly used as a surgical option to offer long-term improvement in the visual quality of patients with KC and to delay corneal transplant. As observed in KC, subsequent structural changes caused by intra and extracellular imbalance may lead to thinning and anterior corneal protrusion. Changes in fibrillar regulation, such as loss of parallelism, interlacing, and reduction of the stromal lamellae portion of the KC, may contribute to the reduction of corneal transparency. Corneal densitometry is determined by an objective, noninvasive, and replicable method which measures the transmission of light through the cornea quantifying its backward dispersion in normal eyes. Thus, densitometric effects due to histological derangement in the KC can be assessed and interpreted. The study aimed was to evaulate the corneal densitometry changes in various annuluses separately for various layers and in the different depths, following the implantation of ICRS assisted by the femtosecond laser for the management of KC.
This was a prospective interventional study included 56 eyes of 40 patients with KC who underwent femtosecond laser-assisted Keraring ICRS implantation at a specialized eye center in Zagazig, during the period of the study from November 2021 to July 2023.
Inclusion Criteria: included age between 15 and 45 years, low visual acuity with glasses, intolerance to contact lenses, clear phakic lenses, and a clear central cornea, with a minimum corneal thickness of at least 350 μm.
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Exclusion criteria: included age below 15 and above 45, corneal scarring and opacities with minimal corneal thickness less than 350 μm, previous corneal refractive or crosslinking surgeries, pseudophakic or cataract, pregnant, previous eye surgery, ocular surface or tear problems and coexistence of ocular pathology other than KC.
All of the patients were subjected to the following:
Preoperative evaluation: All patients were subjected to:
Full medical and surgical his medical and surgical history tory.
Ophthalmic examination: included slit-lamp examination, intraocular pressure measurement, fundus examination, uncorrected and best-corrected visual acuities (UCVA and BCVA in decimal notation), and automated and subjective refraction testing of sphere, cylinder, axis, and spherical equivalent (SE).
Pentacam scheimpflug corneal tomography: was performed to measure front keratometry readings, corneal astigmatism, Q-value, thinnest corneal location thickness (TCLT) and corneal densitometry in all the annular zones.
Surgical procedure: Keraring ICRS implantation with femotosecond laser assisted technique by VisuMax device.
Post-operative evaluation: All the patients were clinically assessed at 1, 7, 30, 60, and 90 days after the surgery. At the final evaluation, UCVA, BCVA, SE, keratometric readings (K1, K2, Km, Kmax), CA, Q-value, TLCT and corneal densitometric values were recorded.
Results of the current study could be summarized as follow:
The mean age of studied patients was 28.99 ± 6.28 years and ranged from 15.33 years to 42.54 years. There was 25 males (62.5%) and 15 females (37.5%), with a male-to-female ratio of 1.67:1.
The preoperative mean K1 was 47.67±4.10, changed to 44.28 ±2.86 postoperatively. The preoperative mean K2 was 51.39±4.74, changed to 46.84 ±3.42 postoperatively.
The preoperative mean Km was 49.44±4.28, changed to 45.45±2.98 postoperatively.
The preoperative mean Kmax was 57.78±7.35 changed to 53.89±5.49 postoperatively.
The preoperative mean Corneal Astigmatism (CA) was 3.73± 2.17 changed to 0.66± 0.49 postoperatively.
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There was significant decline in measurements of K1, K2, Km, Kmax and CA preoperatively compared to postoperative results.
The preoperative mean Q-value was 0.99±0.5 to -0.28±0.5postoperatively.
There was significant increase in Q-value preoperatively compared to postoperatively.
The preoperative mean UCVA was 0.21± 0.12 changed to 0.27± 0.12 postoperatively (P<0.001). Also, the preoperative mean BCVA was 0.44± 0.15 that changed to 0.58± 0.15 postoperatively (P<0.001).
There was significant increase in measurements of UCVA and BCVA postoperatively compared to preoperatively.
The preoperative mean corneal thinnest location thickness was 447.39±34.83 decreased to 450.59± 37.58 after ICRS implantation.
The mean corneal thinnest location thickness after ICRS implantation was not significantly differed compared to before operation.
Except for the annulus 10-12 mm, the mean anterior corneal density increased in all annuluses postoperatively, but this increase was statistically significant only in the annulus 2-6 mm (p = 0.001).
There was a significant elevation in the mean central corneal densitometry measurements in the 2-6 and 6-10 annuluses and total central diameter after ring implantation (p < 0.001, p = 0.047, and p < 0.001, respectively), while the 0-2 mm annulus showed a non-significant increase.
Only the annulus 2-6 mm had a significantly greater density in the posterior corneal layer postoperatively than preoperatively (p < 0.001).
The corneal density of annulus 2-6 mm and total diameter for the total corneal thickness were significantly higher following ICRS implantation when compared to pre-implantation (p < 0.001 and p = 0.014, respectively).
In contrast, a significant reduction in the densitometry readings was observed in the 10-12 annulus for the central, posterior, and total corneal layers following the surgical intervention (p = 0.003, p < 0.001 and p = 0.008, respectively)
The most significant increase in corneal densitometry after ICRS implantation was observed in the 2-6 mm annuluses for all layers and in the central layer among all depths. On the other hand, the density of the 10-12 mm annulus decreased significantly in the central, posterior, and total corneal layers.
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The percentage changes in the central and total 2-6 mm annuluses densities correlated negatively with the percentage changes in the K1 (p=0.025, p=0.029, respectively), K2 (p=0.013 and p=0.021, respectively), and Km (p=0.010 and p=0.014, respectively). Also, in the posterior and total corneal densitometry, there was an inverse correlation between the percentage change in the entire diameter and the percentage changes in the K1 (p=0.004 and p=0.049, respectively), Km (p=0.011 and p=0.034). In addition, a negative correlation was detected between the percentage change in the posterior 0-2 mm annulus density and the percentage change in the K1 (p=0.019).The percentage changes in the corneal densitometry readings did not significantly correlate with the percentage changes in the UCVA, BCVA, and SE, and also with CA and Q value.
The percentage changes in the central and total 2-6 mm annuluses densities correlated negatively with the percentage changes in the K1,K2 and Km.
Also, in the posterior and total corneal densitometry, there was an inverse correlation between the percentage change in the entire diameter and the percentage changes in the K1 and Km.
In addition, a negative correlation was detected between the percentage change in the posterior 0-2 mm annulus density and the percentage change in the K1.
Kmax percentage changes were inversely related with the percentage changes in densitometry measurements in the 6-10 mm and 10-12 mm annuluses and total diameter for the anterior layer (p=0.004, p=0.036 and p=0.012), also with the percentage changes in the central and total 6-10 mm annuluses (p=0.019 and p=0.011, respectively), and with the percentage changes in the total diameter of the posterior layer and the entire thickness (p=0.015 and p=0.003, respectively).