PURPOSE. To analyze the dynamics of all optical components of the eye and the behavior of the eyeball under air-puff conditions in vivo. To determine the impact of the intraocular pressure (IOP) on the air-puff-induced deformation of the eye. METHODS. Twenty eyes of 20 healthy subjects were included in this study. The dynamics of the ocular components, such as the cornea, the crystalline lens, and the retina, was measured by a prototype swept source optical coherence tomography biometer integrated with the air-puff system. The system allows to acquire a series of axial scans at the same location as a function of time with no transverse scanning. Several parameters were extracted from optical coherence tomography data. The IOP was measured using a Goldmann applanation tonometry. The measurements of the eyes were performed before and 2 hours after administration of IOP-reducing drops, namely, 0.2 % brimonidine tartrate. RESULTS. There is a statistically significant correlation of corneal thickness, vitreous depth, and eye length with IOP. The deformation amplitudes of the cornea and the crystalline lens are inversely proportional to the IOP, but statistical significance is achieved only for the cornea. The crystalline lens is displaced without compression, and the return has the form of wobbling. The reduction of IOP level induces corresponding changes in the extracted parameters. CONCLUSIONS. Optical biometry combined with air puff provides comprehensive information on the in vivo behavior of all ocular components, including the crystalline lens. Measurement of the axial length dynamics of during deformation enables correcting the deformation for eye retraction.
Optical coherence tomography (OCT) is a high-speed and non-contact optical imaging technology widely used for noninvasive cross-sectional imaging of biological objects. Two main OCT technologies have been developed: time domain and Fourier domain technologies. The latter can be further divided into spectral domain OCT, which uses a broadband light source and a spectrometer as a detector, and swept source OCT, which employs a quickly-rotating laser source. Advances in OCT technology have made it one of the most helpful devices in ophthalmic practice. Fourier OCT has revolutionized imaging of the posterior segment of the eye, as well as of anterior structures and has enhanced the ability to diagnose and manage patients. It provides high-resolution information about the tear film, contact lens (CL), a qualitative and quantitative assessment of the anterior eye that is important in contact lens fitting, and allows possible eye surface changes while wearing contact lenses to be monitored. Potential swept source OCT technology applications include industrial processes of lens design and quality control. In this paper, we describe clinical applications and outline a variety of multifunctional uses of OCT in the field of refractive error correction with contact lenses.
Purpose: To evaluate refractive and visual outcomes of single-step transepithelial photorefractive keratectomy (transPRK) in the treatment of mixed astigmatism with the use of an aberration-neutral profile and large ablation zone. Setting: Nicolaus Copernicus University and Oftalmika Eye Hospital, Bydgoszcz, Poland. Design: Retrospective, observational case series. Methods: This study included patients who underwent transPRK to correct mixed astigmatism and completed the 3-year follow-up. Procedures were performed with an Amaris 750S excimer laser using an aberration-neutral profile and optical zone of 7.2 mm or more. Results: A total 48 eyes of 39 patients were included. Preoperatively, mean spherical manifest refraction was +1.37 ± 0.98 diopter (D) (0.25 to 4.00 D), and astigmatism was −4.00 ± 0.76 D (−2.25 to −6.00 D). Three years postsurgery, it was −0.17 ± 0.26 D and −0.41 ± 0.44 D, respectively. Attempted spherical equivalent correction within ±0.50 D was achieved in 45 eyes (94%) and cylindrical correction in 34 (71%). Preoperative corrected distance visual acuity (CDVA) was 20/20 or better in 38 eyes (79%), and postoperative uncorrected was 20/20 or better in 29 eyes (60.0%). No eye had lost 2 or more Snellen lines of CDVA, whereas 3 eyes (6%) gained 2 or more lines. In 4 eyes (8%), haze of low intensity was observed at the periphery, with scores between 0.5 and 1.0, and only 1 eye getting a score of 2 in 0- to 4-degree scale. Conclusions: Mixed astigmatism correction with large-ablation-zone transPRK provided good results for efficacy, safety, predictability, and visual outcomes in a 3-year follow-up.
The cornea is a part of the anterior segment of the eye that plays an essential optical role in refracting the light rays on the retina. Cornea also preserves the shape of an eyeball and constitutes a mechanical barrier, protecting the eye against the factors of the external environment. The structure of the cornea influences its biomechanical properties and ensures appropriate mechanical load transfer (that depends on the external environment and the intraocular pressure) while maintaining its shape (to a certain extent) and its transparency. The assessment of the corneal biomechanics is important in clinical ophthalmology, e.g. in the diagnosis of ectatic corneal diseases, for precise planning of the refractive surgery, and in accurate determination of the intraocular pressure. A standard technique to determine corneal biomechanics requires the application of well-defined mechanical stimulus (e.g. air puff) and performing simultaneous imaging of the response of the tissue to the stimulus. A number of methods to assess the biomechanical properties of the cornea have been developed, including ultrasound, magnetic resonance imaging, and optical methods as visualization modalities. Commercially available methods include the ocular response analyzer (ORA) and corneal visualization scheimpflug technology (Corvis ST). Currently advanced research is conducted using optical coherence tomography (OCT). The extension of OCT called optical coherence elastography (OCE) possesses high clinical potential due to the imaging speed, noncontact character, and high resolution of images.
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