To explore the mechanical indices used for differential diagnosis and to investigate the relationship between ocular biomechanics and glaucoma severity within each group.

This cross-sectional study included 185 eyes from 185 subjects: 62 normal controls, 91 high-tension glaucoma (HTG), and 32 normal-tension glaucoma (NTG) patients. All participants underwent a comprehensive ophthalmic examination that involved ocular biomechanical measurements. Glaucoma severity was assessed using visual field index (VFI), mean deviation (MD), pattern standard deviation (PSD) and retinal nerve fiber layer (RNFL) thickness. Multivariable models were used to compare fifteen biomechanical parameters among the three groups adjusting for age, gender, intraocular pressure (IOP), central corneal thickness (CCT), and axial length (AL). The generalized linear model was utilized for multifactor comparison.

Significant differences in first applanation time (AT1), highest concavity time (HC time), stress strain index (SSI), and HC deflection were found among the three groups (P<0.05). AT1 was significantly higher in the HTG group compared to controls (P<0.05), and SSI was higher in HTG than NTG (P<0.05). HC deflection in the HTG group was significantly smaller than in NTG (P<0.05). Furthermore, AT1 levels were observed to be significantly higher in primary open angle glaucoma (POAG) patients compared to controls (P<0.05). Receiver operating charactristic (ROC) analysis showed HC deflection had an area under the curve (AUC) of 0.802 between HTG and NTG. A negatively significant correlation was observed between SSI and VFI in POAG patients.

Biomechanical analysis reveals that corneas in POAG patients are stiffer than normal controls, with increased corneal stiffness correlating with more severe glaucomatous damage. Interestingly, stiffer corneas in NTG patients appeares protective. In addition, HC deflection may be useful for differentiating HTG and NTG.

To explore the clinical efficacy and safety of stromal lenticule addition keratoplasty (SLAK) with corneal crosslinking (CXL) on patients with corneal ectasia secondary to femtosecond laser-assisted in situ keratomileusis (FS-LASIK).

A series of 5 patients undertaking SLAK with CXL for the treatment of corneal ectasia secondary to FS-LASIK were followed for 4-9mo. The lenticules were collected from patients undertaking small incision lenticule extraction (SMILE) for the correction of myopia. Adding a stromal lenticule was aimed at improving the corneal thickness for the safe application of crosslinking and compensating for the thin cornea to improve its mechanical strength.

All surgeries were conducted successfully with no significant complications. Their best corrected visual acuity (BCVA) ranged from 0.05 to 0.8^-2 before surgery. The pre-operational total corneal thickness ranged from 345-404 μm and maximum keratometry (Kmax) ranged from 50.8 to 86.3. After the combination surgery, both the corneal keratometry (range 55.9 to 92.8) and total corneal thickness (range 413-482 μm) significantly increased. Four out of 5 patients had improvement of corneal biomechanical parameters (reflected by stiffness parameter A1 in Corvis ST). However, 3 patients showed decreased BCVA after surgery due to the development of irregular astigmatism and transient haze. Despite the onset of corneal edema right after SLAK, the corneal topography and thickness generally stabilized after 3mo.

SLAK with CXL is a potentially beneficial and safe therapy for advanced corneal ectasia. Future work needs to address the poor predictability of corneal refractometry and compare the outcomes of different surgical modes.