OCTA Analysis of Macular and Papillary Perfusion After Refractive Surgery in Myopes

Myopia is the most prevalent ocular disorder in children worldwide, and one of the major causes of visual deterioration in all age groups. Highest prevalence rates are in East Asian countries (affecting up to 83% of Singaporean teenagers), however, it is very common in all other countries. While mild to moderate myopia usually stabilizes within the third decade, pathological myopia is associated with progressive globe elongation, and development of various macular complications including; foveoschisis, choroidal neovascularization (CNV), myopic macular hole, and myopic vitreomacular traction (VMT).

Refractive surgery has become popular for correcting ametropia including myopia. Most commonly used refractive procedures include corneal refractive surgeries especially laser in-situ keratomileusis (LASIK), and Photorefractive keratectomy (PRK), Phakic Intraocular Lenses (Phakic IOLs) and refractive lens exchange.

In LASIK, the creation of a corneal lamellar flap requires placement of a suction ring on the anterior segment of the eye, which transiently elevates the intraocular pressure (IOP) to levels exceeding 65 mmHg. Experimental studies in animal eyes have found that the IOP can increase to between 80 mmHg and 360 mmHg during this vacuum phase and lamellar cut with the microkeratome. Recent advances utilizing the femtosecond laser may serve as an alternative to the mechanical microkeratome, with a low-pressure suction ring. In studies using porcine eyes, the IOP during the suctioning or laser application phase reached a maximum of 135 mmHg using the femtosecond laser, lower than pressures reached with a traditional microkeratome, but for a longer duration of time. Similarly in refractive lens procedures, intraoperative IOP was found to exceed 60 mmHg.

Intraocular pressure elevation during refractive procedures may cause a reduction in the perfusion of the retina and optic nerve head, posterior displacement of the lamina cribrosa, and a decline in ocular perfusion pressure of the posterior ciliary arteries. Although this IOP elevation is temporary, the potential for ischemic or pressure-induced damage to the optic nerve head and the retinal nerve fiber layer exists.

Optical coherence tomography angiography (OCTA) is a recent noninvasive imaging technique that allows for volumetric visualization of eye vasculature. OCTA has shown promise in better elucidating the pathophysiology of several retinal vascular diseases. Swept-source OCTA uses long wavelength ̰ 1,050nm, which can penetrate through deeper layers of the eye and can traverse opacities of media such as cataracts, hemorrhages and vitreous opacities [6]. Optical coherence tomographic angiograms can further be manually or automatically segmented with preprogrammed software to highlight individual layers of the retina, optic nerve head choriocapillaris, and choroid. The user can either analyze en face images extending from the inner limiting membrane to choroid or use automated views to locate a vascular or structural lesion within the retina.

The purpose of this study is to assess the change of macular and papillary perfusion, using optical coherence tomography angiography (OCTA) imaging of the macula and optic disc of myopic patients subject to various refractive surgery methods. We will compare between these methods to evaluate which one is associated with least adverse effect on ocular perfusion. To date no such evaluation has been done using OCTA, because of relatively recent onset of this technology. Traditional imaging methods such as color fundus photography and fluorescein angiography have limited resolution for retinal vasculature that mad such evaluation in the past using these methods not feasible, however, OCTA is very promising for the proper analysis of changes in the ocular perfusion. Results of this study will have significant clinical and practical implications and may change the approach for surgical correction of such patients.