Corneal Densitometry after Femtosecond Laser-Assisted In Situ Keratomileusis (Fs-LASIK) and Small Incision Lenticule Extraction (SMILE)

Characterization the corneal transparency profile in SMILE-treated myopic patients with densitometry: A 7-year cohort study

PURPOSE

To investigate 7-year changes in corneal densitometry (CD) and its influencing factors following small incision lenticule extraction (SMILE) for moderate to high myopia.

METHODS

A total of 32 patients (52 eyes) with a mean spherical equivalent (SE) refraction of -6.30 ± 1.30 D who underwent SMILE were recruited for this prospective study. Pre- and postoperative CD and corneal aberrations were measured by an oculus Pentacam system, and patients were followed up to 7 years. The CD evolution over time and its influencing factors were explored.

RESULTS

No complications were observed after SMILE. There was a significant time effect on postoperative CD ( P < 0.05). The CD values at the 0-to-2 and 2-to-6 mm of the anterior layer increased at the first day ( P < 0.05) and declined to baselines at 1 year postoperatively; after that, CD values at any zone and any corneal layer presented a decreasing trend over time (all P < 0.05). Multivariate analysis showed that postoperative CD was positively correlated with age and optical zone (OZ), whereas negatively correlated with SE, corrected distance visual acuity (CDVA), and corneal aberrations (higher-order aberrations, Coma0 and Coma90) (all P < 0.05). Generalized estimating equation revealed that age, SE, CDVA, OZ, and Coma0 were the main factors influencing postoperative CD values (all P < 0.05).

CONCLUSION

CD manifested a long-term decreasing trend in moderate to high myopia treated with SMILE. Its main influencing factors are age, SE, CDVA, OZ, and Coma0.

Comparative Study of Primary SMILE, SMILE Enhancement, and Femtosecond Laser-Assisted LASIK on Higher Order Aberrations and Corneal Densitometry

PURPOSE

To compare differences in corneal densitometry (CD) and higher order aberrations (HOAs) in eyes that underwent small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for the treatment of myopia and myopic astigmatism at postoperative months 3, 6, and 12, and to evaluate their changes in a separate cohort of eyes after SMILE enhancement.

METHODS

In this prospective, randomized, paired-eye clinical trial, consecutive eligible participants were randomized to undergo SMILE or FS-LASIK in either eye. Main outcome measures were CD and HOAs preoperatively and at 3, 6, and 12 months postoperatively. A separate cohort of consecutive patients who had SMILE and underwent enhancement were also included for comparison.

RESULTS

For CD, no significant differences were found between SMILE and FS-LASIK up to month 12. For HOA measured by wavefront aberrometry, both SMILE and FS-LASIK had an increase in total root mean square (RMS) HOAs, spherical aberration (SA), and vertical coma up to month 12. SMILE had an additional increase in vertical quatrefoil, and FS-LASIK had an increase in horizontal coma at month 12. FS-LASIK had higher SA than SMILE, whereas SMILE had higher vertical quatrefoil than FS-LASIK at month 12. Central and posterior zone CD had significantly decreased after SMILE enhancement compared to after primary SMILE up to 2 years after enhancement. RMS HOAs, lower order aberrations, and SA were all increased after SMILE enhancement compared to after primary SMILE.

CONCLUSIONS

SMILE induced lower SA but higher vertical quatrefoil than FS-LASIK at 1 year. Both SMILE and FS-LASIK had similar increases in RMS HOAs and vertical coma up to 1 year. There were no differences in CD between both groups. SMILE enhancement additionally had decreased central and posterior CD but greater RMS HOAs and SA compared to primary SMILE. [J Refract Surg. 2024;40(5):e291-e303.].

Visual outcomes and corneal densitometry after allogenic and autologous lenticule intrastromal keratoplasty for the correction of moderate-to-high hyperopia

AIM

This study aimed to evaluate the visual outcomes and corneal densitometry (CD) after allogenic lenticule intrastromal keratoplasty (AL-LIKE) and autologous lenticule intrastromal keratoplasty (AU-LIKE) for the correction of moderate-to-high hyperopia.

METHODS

Ten subjects (14 eyes) underwent AL-LIKE and eight (8 eyes) underwent AU-LIKE. Patients were examined preoperatively and 1 day, 1 month, and 6 months postoperatively. The visual outcomes and CD for both surgical methods were evaluated.

RESULTS

No postoperative complications were observed with either method. The efficacy index was 0.85±0.18 and 0.90±0.33 in the AL-LIKE and AU-LIKE groups, respectively. The safety indices were 1.07±0.21 and 1.25±0.37 in the AL-LIKE and AU-LIKE groups, respectively. The CD values of the anterior, central, and posterior layers in the AL-LIKE group increased significantly at 1 day postoperatively (all P < 0.05). The CD values of the anterior and central layers remained significantly higher than the preoperative values at 6 months postoperatively (all P < 0.05). The CD values of the anterior layer in the AU-LIKE group increased significantly 1 day postoperatively (all P < 0.05) and decreased to preoperative values (all P > 0.05) 1 month postoperatively.

CONCLUSION

Both AL-LIKE and AU-LIKE exhibit good efficacy and safety in correcting hyperopia. However, AU-LIKE may have a smaller affected area and faster recovery time than those associated with AU-LIKE related to changes in corneal transparency.

Seven-year corneal densitometry changes after small incision lenticule extraction and femtosecond laser-assisted in situ keratomileusis

This study aims to investigate the 7-year changes in corneal densitometry (CD) after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). Forty-two eyes undergoing SMILE and thirty-one undergoing FS-LASIK were included in this retrospective study. CD was measured preoperatively and at 3 and 7 years postoperatively. Three concentric radial zones (0-2, 2-6, and 6-10 mm) of three different corneal depths (anterior 120 μm, posterior 60 μm, and central layer) were analyzed. In all three zones of the three corneal layers, no significant difference in CD was found between the two groups preoperatively and at 3 and 7 years postoperatively (all P > 0.05). All CD values in the three zones of the anterior and central layers significantly declined at 3 years postoperatively (all P < 0.001), and then increased at 7 years postoperatively compared to corresponding 3-year values (all P < 0.01). In the posterior layer, CD values in the 0-2-mm and 2-6-mm zones decreased at 3 years postoperatively (all P < 0.01) and continued to decrease at 7 years postoperatively (all P < 0.01). Similar CD trends were observed after SMILE and FS-LASIK. Posterior layer CD showed a decrease throughout the study period. In the anterior and central layers, CD values decreased and then increased at 7 years postoperatively. The transparency changes might have been due to age-related three-dimensional growth of collagen fibers and wound-healing reactions.

Corneal optical density: Structural basis, measurements, influencing factors, and roles in refractive surgery

The cornea is the main refractive medium of the human eye, and its clarity is critical to visual acuity. Corneal optical density (COD) is an important index to describe corneal transparency. Intact corneal epithelial and endothelial cells, regular arrangement of collagen fibers in the stroma, and normal substance metabolism are all integral for the cornea to maintain its transparency. In the last two decades, the Pentacam Scheimpflug imaging system has emerged as a breakthrough for the measurement of COD (also called corneal densitometry). It has been found that a wide variety of factors such as age, refractive status, and corneal diseases can affect COD. Different corneal refractive surgery methods also change COD in different corneal regions and layers and affect visual acuity following the surgery. Thus, COD has gradually become a significant indicator to evaluate corneal health, one on which the attention of clinicians has been increasingly focused.

Comparison of Corneal Densitometry and Visual Quality after Small Incision Lenticule Extraction (SMILE) and Laser Epithelial Keratomileusis (LASEK): One-Year Comparative Study

Purpose

To investigate changes in corneal densitometry (CD) and visual quality following small incision lenticule extraction (SMILE) and laser epithelial keratomileusis (LASEK) in patients with mild-to-moderate myopia.

Methods

A retrospective analysis was performed on 24 and 25 patients (46 eyes each) who underwent SMILE and LASEK, respectively, for mild-to-moderate myopia. The visual quality and CD values were recorded. Using the Pentacam Scheimpflug system, CD values were collected in three concentric optical zones at the depths of the anterior, central, and posterior layers. Efficacy, safety, predictability, corneal wavefront aberrations, and QoV scores were measured to evaluate visual quality. A correlation analysis was performed between changes in CD and clinical characteristics.

Results

There were no statistical differences in efficacy and safety indices between the two groups. At 3 months postoperatively, a pronounced reduction in several zones was observed in the LASEK group (p < 0.05), whereas no obvious change was observed in the SMILE group. There were obvious changes in the CD values in several zones in the SMILE and LASEK groups (p < 0.05) after 1 year. The magnitude of the CD changes in the anterior and central corneal layers was smaller in the SMILE group than in the LASEK group (all p < 0.05). Lower HOAs, spherical aberration, and horizontal comas of the anterior and whole corneal surfaces were observed in the SMILE group. QoV scores were similar between the two groups.

Conclusion

CD decreased in the SMILE and LASEK groups after 1 year; there was a smaller reduction in SMILE than in LASEK. SMILE and LASEK did not differ significantly in terms of safety and effectiveness in correcting mild-to-moderate myopia.

In vivo confocal microscopy of sub-basal corneal nerves and corneal densitometry after three kinds of refractive procedures for high myopia

PURPOSE

To observe corneal nerve fibers and densitometry after small incision lenticule extraction (SMILE), femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) and laser-assisted subepithelial keratomileusis (LASEK) for high myopia.

METHODS

This is a prospective, cross-sectional research study. Patients with high myopia (equivalent spherical lens: -6.00 and -11.00D) who underwent laser corneal refractive surgery were divided into three groups: SMILE, FS-LASIK and LASEK. Scheimpflug imaging of corneal nerves in five areas was observed by confocal microscopy before and 6, 12 months after surgery. Corneal densitometry was measured by Pentacam anterior segment analysis system.

RESULTS

Overall, 59 patients were enrolled. The nerve density in the central area did not recover to the preoperative level in three groups until 12 months. The density and length of corneal nerves in central and lower area were better in the SMILE group 6 months postoperatively (p = 0.01), while nerve density did not differ significantly among three groups 12 months postoperatively (p = 0.18). Nerve fibers in central and temporal region were wider in LASEK than that in other two groups at 6- and 12-month follow-up. Corneal densitometry in the central 6 mm diameter was significantly higher in the LASEK group compared with other two groups 6 months postoperatively (p = 0.04). Twelve months postoperatively, corneal densitometry in range of all zone was lower in SMILE than in FS-LASIK and LASEK (p = 0.01, 0.03, 0.04).

CONCLUSIONS

Compared with FS-LASIK and LASEK, SMILE-treated eyes with high myopia had certain advantages in nerve density, length and nerve connection way and had better corneal transparency after operation.

Long-term changes in corneal densitometry and associated factors following small incision lenticule extraction for moderate and high myopia

Purpose

To investigate long-term trends in corneal densitometry and associated influencing factors following small incision lenticule extraction (SMILE).

Methods

A comparative study was performed among 72 eyes of 38 patients undergoing SMILE. Eyes were divided into moderate myopia [mean spherical equivalent (SE),−4.22 ± 0.68D] and high myopia (mean SE,−7.63 ± 1.09 D) groups. Visual acuity, manifest refraction, corneal topography and corneal densitometry (CD) were evaluated preoperatively and 3 years postoperatively.

Results

The efficacy indices at last postoperative follow-up (42.47 ± 0.51 months) were 0.92 ± 0.21 and 0.97 ± 0.22, the safety indices were 1.12 ± 0.17 and 1.14 ± 0.21 for high and moderate myopia, respectively (all P > 0.05). CD values in the 0–6 mm zone of the posterior corneal layer was statistically significantly lower than the preoperative values in both groups. Postoperative CD values (0–2 mm zone) in the posterior layer of the high myopia group were statistically significantly lower than in the moderate myopia group (P = 0.025); CD values (2–6 mm zone) in the anterior layer were higher in the high myopia group (P = 0.026). Correlation analyses showed that CD values in the 0–2 mm middle layer were negatively correlated with lenticule thickness in high myopia (r = −0.411, P = 0.016); there was a negative correlation between the CD values (0–6 mm) and corneal oblique trefoil in this group (P < 0.05).

Conclusion

Corneal transparency in the 0–6 mm zone of the posterior cornea increased following SMILE in moderate and high myopia. Long-term CD values in high myopia may be correlated with oblique trefoil and lenticule thickness.

Corneal densitometry after allogeneic small-incision intrastromal lenticule implantation for hyperopia correction

Purpose

To evaluate corneal densitometry after allogeneic corneal small-incision intrastromal lenticule implantation (SILI) for hyperopia.

Methods

A retrospective study. Thirty-one hyperopic eyes of 24 patients who underwent SILI were enrolled in this study. Examinations took place preoperatively and 1 week, 1 month, 3 months, and 6 months postoperatively. Corneal densitometry (CD) from different concentric radial zones (0–2, 2–6, and 6–10 mm annulus) and layers (anterior, central, and posterior) were obtained using Scheimpflug imaging. The association between CD changes and the uncorrected distance visual acuity (UDVA), spherical equivalent (SE), central corneal thickness (CCT) and K value were examined.

Results

No serious intraoperative complications occurred during SILI. The mean total CD increased postoperatively compared to preoperatively (P < 0.01). However, no significant differences were found among the four subsequent follow-up time points (P > 0.05). At 6 months postoperatively, the CD values showed an increase of 2.71 ± 2.52, 2.23 ± 2.25, and 1.87 ± 2.46 at the 0–2, 2–6, and 6–10 mm annuli, respectively (all at P < 0.01). The anterior 120 μm displayed the highest densitometry before and after surgery (all at P < 0.01). No significant increase was found within the posterior 60 μm of the cornea (P > 0.05). No correlation was found between the CD and relevant parameters(all at P > 0.05).

Conclusions

SILI resulted in an increase in CD within the surgically altered area, however such change has no significant correlation with visual outcomes.

Changes in corneal densitometry after long-term orthokeratology for myopia and short-term discontinuation

Purpose

To quantify changes in corneal densitometry after long-term orthokeratology treatment in myopic children and to analyze the reversibility one month after discontinuation.

Methods

Seventy-four myopic subjects aged 8–16 years, who wore orthokeratology lenses for two years, were divided into relatively steep- (lens movement within 1.0–1.5 mm, thirty-six participants) and flat-fitting groups (lens movement within 1.5–2.0 mm, thirty-eight participants). Based on refractive errors, they were divided into low and moderate myopia groups (thirty-seven participants in each group). Corneal densitometry was performed using Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) at each follow-up timepoint. Repeated-measures analysis of variance was used to compare the parameters before and after orthokeratology.

Results

The corneal densitometry values over the 0–10 mm diameter area increased from 12.84±1.38 grayscale units (GSU) at baseline to 13.59±1.42 GSU after three-month orthokeratology (P = .001) and reached 14.92±1.45 GSU at two years (P < .001). An increase in densitometry began at one month (P = .001) over the 0–2 mm annulus compared with that at three months over the 2–6 mm and 6–10 mm zones (P = .002,.014). The densitometry values significantly increased at three months in the relatively steep-fitting group (P = .003) and at one year in the relatively flat-fitting group (P = .001). After discontinuation of orthokeratology for one month, the values showed no significant decrease.

Conclusions

Long-term orthokeratology treatment causes a small but statistically significant increase in corneal densitometry values. During the first year, the onset of these changes was related to the fitting mode. Corneal densitometry values showed no significant reduction after one-month discontinuation.

Corneal Light Scatter After Ultrathin Descemet Stripping Automated Endothelial Keratoplasty Versus Descemet Membrane Endothelial Keratoplasty in Descemet Endothelial Thickness Comparison Trial: A Randomized Controlled Trial

PURPOSE

To compare the degree of corneal light scatter as measured by densitometry in ultrathin Descemet Stripping Automated Endothelial Keratoplasty (UT-DSAEK) and Descemet Membrane Endothelial Keratoplasty (DMEK) in the Descemet endothelial thickness comparison trial.

METHODS

This was a prespecified secondary analysis of the Descemet endothelial thickness comparison trial, which was a prospective, randomized controlled trial. Subjects with isolated endothelial dysfunction were enrolled and were randomized to either UT-DSAEK or DMEK. Corneal opacity was quantitatively measured by Pentacam densitometry (OCULUS) at 3, 6, and 12 months.

RESULTS

Fifty eyes of 38 patients were enrolled at the Casey Eye Institute at Oregon Health & Science University and the Byers Eye Institute at Stanford University. Corneal densitometry for the anterior and posterior layers improved in both UT-DSAEK and DMEK after surgery. The decrease was more pronounced in the posterior layer for both groups. However, there was no difference in the degree of corneal light scatter between UT-DSAEK and DMEK at postoperative month 12, and no difference in change in densitometry was observed between the 2 arms from baseline to month 12.

CONCLUSIONS

Both UT-DSAEK and DMEK experience an improvement in the degree of corneal light scatter after surgery. However, there was no difference in densitometry between the 2 groups at month 12. Therefore, other factors such as higher order aberrations in the posterior cornea rather than stromal-stromal interface haze mediate the superior visual outcomes in DMEK compared with UT-DSAEK.

Corneal Densitometry After Small Incision Lenticule Extraction (SMILE) and Femtosecond Laser-Assisted LASIK (FS-LASIK): 5-Year Prospective Comparative Study

Purpose: To investigate long-term changes in corneal densitometry (CD) following small incision lenticule extraction (SMILE) vs. femtosecond laser-assisted LASIK (FS-LASIK) in patients with myopia or myopic astigmatism.

Methods: Prospective analysis was performed in 66 eyes of 38 patients (13 males) who underwent SMILE and 54 eyes of 29 patients (5 males) who underwent FS-LASIK. In all patients, an ocular examination was performed preoperatively, and at 6–12 months and 5 years postoperatively. CD was obtained with the Pentacam Scheimpflug imaging system at the 0–2-mm, 2–6-mm, and 6–10-mm zones of the cornea at depth of anterior 120 μm, midcornea, and posterior 60 μm. Correlation analysis was performed between postoperative change in CD and other variables such as age, type of surgery, central corneal thickness, spherical equivalent, lenticule thickness/ablation depth, and changes in wavefront aberrations.

Results: At postoperative 6–12 months, a significant reduction at several corneal zones in the FS-LASIK cohort (P < 0.05) was observed. In the SMILE cohort, no significant change in CD relative to baseline was observed. However, at 5 years postoperatively, in both groups, a significant decrease in CD was observed in three zones of three layers (all P < 0.001). The change in CD was similar between groups at postoperative 6–12 months, but at 5 years the magnitude of change was significantly smaller in SMILE than FS-LASIK in the anterior and central layers (all P < 0.05).

Conclusion: CD with the Scheimpflug imaging system showed a significant decrease at 5 years after SMILE or FS-LASIK, and the change was significantly less pronounced after SMILE.

Evolution of corneal thickness and optical density after laser in situ keratomileusis versus small incision lenticule extraction for myopia correction

PURPOSE

To compare the thickness and stromal optical density (OD) evolution of the flap and cap after femtosecond (FS-LASIK; Visumax) and small incision lenticule extraction (SMILE), respectively, for myopia correction.

METHODS

A prospective study comprising 78 eyes (n=39 per group) was performed. Anterior segment optical coherence tomography (MS39) images were collected at each postoperative visit (1 day, 1 week and 1 and 3 months) and flap/cap thicknesses were measured. Using ImageJ software, three regions were defined to measure OD (in grayscale units: flap/cap stroma, residual stromal bed (RSB) and all stroma (including flap/cap-stroma, surgical interface and RSB).

RESULTS

Mean central thickness significantly increased during the 3-month follow-up in both LASIK (5.43±4.23 μm; p=0.0118) and SMILE (2.76±5.61 μm; p=0.0118), with differences between both techniques statistically significant (p=0.020). All OD values showed a statistically significant reduction during SMILE follow-up: cap 48.96±5.55 versus 44.95±5.41 (p=0.19×10^-6), RSB 50.26±7.06 versus 45.42±7.53 (p=0.00005), total stroma 50.34±6.49 versus 45.46±6.96 (p=0.5×10^-5) at 1 day and 3 months, respectively, whereas no statistically significant changes were found during LASIK follow-up. No significant differences were observed in OD values between both techniques at any time point, although SMILE showed a tendency for higher OD values than LASIK within the first postoperative month. Visumax presented a tendency for thicker caps than target (11.48±7.85 μm), but not for flaps (2.73±8.93 μm) (p=0.00003).

CONCLUSIONS

Both LASIK flaps and SMILE caps show a significant postoperative rethickening. SMILE corneas present higher optical densities than LASIK corneas in the early postoperative period, with a significant decrease thereafter and up to 3 months. These findings correlate with the delayed visual recovery observed after SMILE.