Adaptive modal gain controlling for a high-efficiency cylindrical vector beam fiber laser.

We propose and experimentally demonstrate an ytterbium-doped fiber laser emitting the single high-order cylindrical vector beams with a high efficiency and a high modal purity based on adaptive modal gain control. By the combination of a high-order pump with a self-designed ytterbium-ring doped fiber, modal dependent gain was tailored and specific transverse mode can be selected in the laser cavity. A model based on multimode propagation-rate equations is built up to demonstrate the behaviors of transverse mode competition in the fiber laser. Modal dependent gain of high-order mode pump are simulated numerically, which agree well with our experiment results. The slope efficiency of the fiber laser reaches 79.61% with a low threshold of 47.73mw. The purity of the generated high-order CVBs are in excess of 95%. Such a strategy enables the controllability of modal gain in a fiber laser and reveals the potential to offer a new and promising way to achieve a high-power fiber laser with an arbitrary single high-order transverse modes output.

Ten-year observation of corneal densitometry and associated factors following small incision lenticule extraction.

AIM: To investigate the long-term changes of corneal densitometry (CD) and its contributing elements after small incision lenticule extraction (SMILE). METHODS: Totally 31 eyes of 31 patients with mean spherical equivalent of -6.46±1.50 D and mean age 28.23±7.38y were enrolled. Full-scale examinations were conducted on all patients preoperatively and during follow-up. Visual acuity, manifest refraction, axial length, corneal thickness, corneal higher-order aberrations, and CD were evaluated. RESULTS: All surgeries were completed successfully without complications or adverse events. Ten-year safety index was 1.17±0.20 and efficacy 1.04±0.28. CD value of 0-6 mm zones in central layer was statistically significantly lower 10y postoperatively, compared with preoperative values (0-2 mmΔ=-1.62, 2-6 mmΔ=-1.24, P<0.01). There were no correlations between CD values and factors evaluated. CONCLUSION: SMILE is a safe and efficient procedure for myopia on a long-term basis. CD values get lower 10y postoperatively, whose mechanism is to be further discussed.

[The clinical study of femtosecond lenticule extraction for myopia].

OBJECTIVE: To evaluate the clinical efficacy, safety and predictability of femtosecond lenticule extraction (FLEx) for myopia. METHODS: This is a prospective Clinical trial involved 10 cases (10 eyes). The patients aged from 18 years old to 53 years old, an average of (34 ± 11) years old. Femtosecond lenticule extraction (FLEx) was used to treat myopia from -4.88 DS to -9.25 DS, an average of (-6.94 ± 1.50) DS with cylinder from 0.50 DC to 3.0 µm DC an average of (1.28 ± 0.73)DC. Their corneal thickness were (527.10 ± 29.05) µm in an average. The patients were followed up for 6 to 10 months with visual acuity, manifest refraction, intraocular pressure, wavefront aberration, corneal topography and optical coherence tomography (OCT). SPSS software was used to analysis. RESULTS: FLEx procedure was done well in every patients without any scanning problem. No infection happened to in the trial. The patients' UCVA improved to 0.6 - 1.2 while BCVA improved 0.7 - 1.2 postoperatively. BCVA improved more than 2 lines in 2 eyes whereas 1 line in 2 eyes. No eye lost BCVA. The difference between pre-and postoperative refraction was within ± 0.75 DS, an average of SE (-0.25 ± 0.33) DS. No epicenter showed in topography. Spherical aberration increased slightly in 8 eyes but decreased in 2 eyes. OCT showed that stroma bed fit to each other very well. CONCLUSION: Femtosecond lenticule extraction appears to be efficiency, safety and predictable for myopia. Femtosecond lenticule extraction could have a good stroma fit. Its wavefront aberration changes need to further investigation.

[Analysis of flap thickness by anterior segment optical coherence tomography in different flap preparation styles of excimer laser surgery].

OBJECTIVE: To assess and compare the accuracy and regularity and short-term change of corneal flap in different flap preparation styles. METHODS: Eighty eyes of 40 cases were treated with laser-assisted subepithelial keratectomy. One hundred and fifty-five eyes of 78 cases were treated with laser in situ keratomileusis with 90 microm microkeratome flap preparation and eighty-two eyes of 42 cases were treated with laser in situ keratomileusis with 100 microm femtosecond laser flap preparation. Anterior segment optical coherence tomography was used to assess the thickness of epithelial or stromal flaps created with M2 microkeratome or VisuMax femtosecond laser by the same investigator 1 hour, 1 day, 1 week, 1 month and 3 months postoperatively, respectively. The thickness of twenty-five measuring points across each flap in LASIK, which were 1.5 mm, 2.5 mm and 3.5 mm away from vertex of cornea on the horizontal, vertical, 45 degrees and 135 degrees meridian respectively and the vertex of cornea itself, was evaluated. The results were analyzed with t-test or ANOVA by SPSS software. RESULTS: The thickness of epithelial flaps was (57.91 + or - 6.76), (54.94 + or - 4.65), (54.96 + or - 2.70), (55.26 + or - 4.27) and (53.86 + or - 5.56) microm at 1 hour, 1 day, 1 week, 1 month and 3 months respectively, with statistical significant difference between 1 hour and the other time points (F = 20.25, P < 0.05). The average thickness of stromal flaps on the vertex of cornea in microkeratome group was (129.16 + or - 12.10) microm, while (112.69 + or - 5.12) microm in the femtosecond laser group, which means the accuracy of flap preparation with femtosecond laser is better than with microkeratome. The absolute difference between actual and average thickness was (13.16 + or - 4.78) and (5.26 + or - 1.21) microm in the microkeratome group and femtosecond laser group, which means the reproducibility of flap preparation with femtosecond laser is better than with microkeratome as well. Flap morphology showed the feature of thin central area and thick peripheral area in microkeratome flap and uniformity in femtosecond laser flap, which illustrated the better regularity of femtosecond laser flap preparation. CONCLUSIONS: Anterior segment optical coherence tomography is a safe, quick and reliable facility to examine and assess flap morphology. Our results showed the accuracy and regularity of femtosecond laser flap preparation outweighed microkeratome flap preparation.

[Clinical study of diffuse lamellar keratitis after laser in situ keratomileusis].

OBJECTIVE: To investigate a new clinical grading scale of diffuse lamellar keratitis (DLK) following laser in situ keratomileusis (LASIK) and to observe the clinic outcomes of eyes treated with corresponding classified therapy. METHODS: It was a prospective case-control study. Eyes that developed DLK after LASIK were diagnosed by a new criterion of clinical grading scale based on both severity and scope of inflammatory cells infiltrations in the corneal interface. Dose and frequency of topical or systemic corticosteroid were determined by the classified profiles according to each grade. Clinical symptoms, corneal inflammatory cells infiltrations, visual acuity, refractive error and intraocular pressure (IOP) were evaluated on 1, 3, 5, 7, 10 days and 1 month after diagnosis as well as at the time of diagnosis. RESULTS: Among the 35 eyes of 29 patients that developed DLK, mild inflammatory cells infiltrations were mostly seen. Thirty eyes had degree I DLK and 3 had degree II DLK. One eye had degree III DLK and one had degree IV DLK. Inflammatory cells infiltrations in 20 eyes invaded peripheral zone (zone 1) and those in 11 eyes invaded mid-peripheral zone (zone 2). Inflammatory cells infiltrates in 4 eyes invaded central zone (zone 3). Nineteen eyes had degree I zone 1 DLK. Thirty three eyes were diagnosed between the 1st day and the 3rd day after surgery. Uncorrected visual acuity (UCVA) was worse than preoperative best spectacle corrected visual acuity (BSCVA). Inflammatory cells infiltrations retreated within 6.06 2.04 days after classified corticosteroid therapy. One month after the treatment, UCVA had improved to the level of preoperative BSCVA. BSCVA in 30 eyes were equal to or better than those before surgery. Spherical equivalent of the refractive error was (-0.21 +/- 1.16) D. There was no statistic difference in the retreat time of inflammatory cells infiltrations, recovery of visual acuity and refractive error among the different grades of DLK or among the DLK treated with different therapy profiles. No eye suffered from high intraocular pressure during the treatments. CONCLUSIONS: Clinical grading scale and corresponding classified therapy were proved to be effective in the treatment for DLK.

[Recovery of corneal sensitivity in extremely high myopia after laser sub-epithelium keratomileusis].

OBJECTIVE: To evaluate the changes in corneal sensitivity following laser epithelial keratomileusis (LASEK) and epiploic laser in situ keratomileusis (Epi-LASIK) in treatment of extremely high myopia. METHODS: Thirty-seven eyes of 37 patients underwent LASEK and Epi-LASIK to correct myopia, their equivalent sphere ranged from -9.50 DS to -12.50 DS, astigmatism < +/- 1.50 DC. Cornea sensitivity was measured with a Cochet-Bonnet esthesiometer at central part of the cornea. Treated eyes were divided into two groups by different operation methods: Epi-LASIK group and LASEK group. After the operation, each group was divided into two sub-groups according to the eyes with or without obvious epithelium edema. RESULTS: Obvious epithelium sheet edema happened in 6 eyes after LASEK and 3 eyes among them were due to broken epithelium sheets during the operation. By 2 weeks, 1, 2, 3 and 6 months after Epi-LASIK, corneal sensitivity recovered to 79.31%, 84.49%, 87.92%, 92.24% and 93.98% of preoperative level, respectively. Compare to the Epi-LASIK, cornea sensitivity after LASEK recovered to 69.64%, 78.57%, 83.21%, 85.70% and 87.86% of preoperative level, respectively. The recovery of corneal sensation in LASEK group was slower than that of Epi-LASIK group. The difference between these two groups was statistically significant at 2 weeks after the operation (P < 0.05). In LASEK group, there was a trend towards a great reduction in corneal sensitivity in epithelium edema eyes and the recovery was slower in these eyes. The difference of corneal sensitivity recovery between these two sub-groups was statistically significant (P < 0.05). CONCLUSION: The recovery of corneal sensitivity in extremely high myopia after Epi-LASIK is faster than that after LASEK, and reached to the platform stage by 3 months. The epithelium sheet edema after LASEK affects corneal sensitivity recovery.

[Effects of short-term VDT usage on visual functions].

OBJECTIVE: To evaluate the effects of short-term VDT usage on visual functions. METHODS: Visual function of the video display terminal (VDT) operators before and after 1 hour VDT usage were assessed. These included refraction, amplitude of accommodation, near point of convergence, AC/A, phorias, fusional convergence and divergence, tear film break time (BUT) and aberrations. And the same situation was compared was the non-VDT usage. RESULTS: In comparison with pre-VDT use, amplitude of accommodation, BUT were significantly decreased (P < 0.05), near point of convergence, near lateral exophoria were significantly increased after VDT use (P < 0.05). Total, high order, 4th and 5th order aberrations were significantly greater after VDT use (P < 0.05). CONCLUSIONS: Short-term VDT work does have a significantly greater temporarily effect on visual function, tear film quality and visual quality.