EyeWorld China September 2019 Issue

Early clinical experience with Streamlight Dr. Rick Wolfe StreamLight TM transepithelial PRK results in quicker surgery, faster healing and better patient satisfaction. StreamLight TM should be used where wavefront optimized PRK profiles are planned. Special care of post-surgical eyes with thick and irregular epithelium is essential. StreamLight TM (EX500 transPRK) is the latest, no-touch, one-step technology used to perform Trans-Epi photorefractive keratectomy (PRK) in patients who cannot have a LASIK flap. Epithelial mapping should be used to determine corneal abnormalities before performing transepithelial PRK. Custom Q for Presbyopes Prof Zhang Fengju 11 Figure 6: Reduction in recurrent corneal erosions with T PRK Early clinical experience with StreamLight TM , the latest no-touch, one-step technology used to perform trans-epithelial photorefractive keratectomy (Trans-Epi PRK) has been promising. Potential advantages of StreamLight TM include faster surgery (2sec/D), better patient acceptance due to its no-touch mechanism, and quicker treatment with one-step technique. In addition, it has been shown to be associated with faster healing and less pain, with better or equivalent results compared to conventional PRK. Reduction in incidenceof complications, particularly recurrent corneal erosion syndrome (RCES) (Figure 6) is an a software designed to assist in calculations for Contoura LASIK treatments. “Phorcides has the potential to make Trans-epi PTK very predictable for irregular corneas by assessing the refractive effect of a PTK of given depth on a particular epithelial layer. It has the potential to regularize the cornea and achieve refractive predictability simultaneously”, added Dr. Cummings. additional advantage, 5 stated Dr. Rick Wolfe. A point to be noted during Trans-Epi PRK is the increase in local corneal temperature due to higher energy load. The normal corneal surface temperature is around 32.9 to 36 °C, and temperature above 40 °C may denaturize collagen proteins resulting in tissue damage and reduced refractive outcomes. “This is an important issue and should bemanaged effectively,” added Dr. Wolfe. A study of Trans-Epi PRK using 750 Hz excimer laser system showed that the maximum temperature reached was up to 39.7º, with the use of special software that reduced the thermal load. 6 Presbyopia is a loss of accommodative amplitude that occurs with age. Presbyopia can be treated by static methods (e.g. monovision, corneal inlays) that increase the depth of focus or by dynamic methods (e.g. scleral implants and accommodative IOLs), which try to restore accommodation. 7 Normal cornea is aspheric in shape (prolate shape) that gradually reduces its refractive power towards periphery, merging all rays of light to a single focus and reducing the spherical aberration. On the other hand, the combination of monovision (central rays are focused in front of the retina) and a hyperprolate cornea (peripheral rays are focused behind the central rays) creates a larger depth of field, inducing a negative spherical aberration, by an adjusting the corneal asphericity factor (Q factor). This type of treatment is called the CustomQ, stated Prof. Zhang. Though Custom Q allows the surgeon to customize target refraction and corneal asphericity, certain pre-requisites for Custom Q need to be followed to ensure successful outcome (Table 7). “Besides theconventional pre-operativeexamination, the most important test before starting Custom Q is the tolerance test for monovision procedure. It is essential to counsel the patient, lower his expectation and inform about the possibility of enhancement.” cautioned Prof Zhang.