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Preclinical Toxicology/Safety Considerations in the Development of Ophthalmic Drugs and Devices
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Robert B. Hackett, Michael E. Stern
Evaluation of the strength and ability of the corneal stroma to heal and withstand trauma is extremely important in evaluating the effects of topical and intraocular formulations. This impacts on postoperative healing of corneal transplants, cataracts, and refractive surgeries such as radial keratotomy and epikeratophakia. In this technique a 9 mm corneal incision is placed in the central cornea and closed with four interrupted 10.0 nylon sutures. The cornea is allowed to heal for a predetermined period of time (usually 6 to 9 days). At this time the rabbit is humanely euthanized and a needle is placed in the anterior chamber which is attached to an infusion pump. Another needle is placed in the anterior chamber which is attached to a pressure transducer and physiograph. As saline is pumped into the eye, the pressure increases and is recorded by the transducer and physiograph. The pressure increases until the incision fails, which is marked by a sudden decrease in monitored pressure. The peak of the pressure curve is called the bursting pressure.9 This pressure can be compared to others in corneas treated with test formulations, either topically or intraocularly. Steroids, for example, are known to decrease the bursting pressure of a corneal wound at various time points.
The Special Sense Organs and Their Disorders
Published in Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss, Understanding Medical Terms, 2020
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss
Disorders of the visual senses are usually referred to a specialist in treating eye disorders. An ophthalmologist or oculist is a physician who specializes in diseases and surgery of the eye. An optometrist is qualified to examine the eyes for vision problems and eye disorders and to prescribe lenses and other optical aids. The specialist who fills prescriptions for lenses, dispenses the eyeglasses, and makes and fits contact lens is an optician. Radial keratotomy (kerat = cornea, -otomy = incision) is a commonly used corrective surgical technique. A newer method utilizes a laser device and is referred to as photoreflective keratotorny. A keratoplasty, sometimes called a corneal transplant, involves replacing a section of diseased cornea with a normal one.
Eyesight standards for beach lifeguards
Published in Mike Tipton, Adam Wooler, The Science of Beach Lifeguarding, 2018
As the above information suggests, the international picture is mixed. For example, the vision requirements for bay and ocean lifeguards in the city of San Diego, California, include uncorrected vision no worse than 20/40 (see text below for explanation of these figures) in both eyes together with ‘acceptable’ colour vision. Vision between 20/20 and 20/40 in both eyes together must be corrected to 20/20 both eyes together with glasses or contact lenses. Monocular vision is not acceptable. Those who have undergone any type of refractive vision surgery such as laser-assisted in situ keratomileusis (LASIK), radial keratotomy or photo refractive keratectomy a year or longer prior to being medically considered for a lifeguard position must be substantially free of vision problems such as impaired vision at night or under dim lighting conditions; sensitivity to glare; starbursts experienced around light sources such as street lights or headlights, hazing or blurring of vision, eye irritation and pain, progressive regression of visual acuity and daily changes in visual acuity (http://agency.governmentjobs.com/sandiego/job_bulletin.cfm?JobID=334906, 2013). In the United Kingdom, the Royal National Lifeboat Institution (RNLI) allows beach lifeguards to wear glasses on the beach, provided lifeguards meet the RNLI’s eyesight standard of 6/24, 6/36 (correcting to 6/6, 6/12). A new applicant who wears glasses or contact lenses or who has had eye surgery is asked to see an optician for a sight test and is not passed medically fit until this is confirmed.
Risk factors for complications during phacoemulsification cataract surgery
Published in Expert Review of Ophthalmology, 2020
Manpreet Kaur, Nithya Bhai, Jeewan S. Titiyal
Leaky wounds should be sutured at the end of surgery. In addition, it is preferable to suture the wound in cases with difficult anatomy such as high myopia, corneal ectasia, post-RK cases and healed keratitis. In corneas with topographical changes like keratoconus, temporal corneal incisions closer to the limbus that do not potentially disrupt the thinner ectatic cornea are preferred[19]. Wound creation can be complicated by induced astigmatism and progressive ectasia and may not result in a self-sealed wound. Sutured incisions are safer and provide an additional chance to improve refraction and regularize astigmatism in these cases [20–22]. In eyes with radial keratotomy (RK), the corneal incision should be at the posterior limbus in the gap between two RK cuts so as to avoid transection of the prior RK incisions. Placing a corneal suture over the RK scars, adjacent to the main incision stabilize and reduce the risk of dehiscence of RK cuts during phacoemulsification and have a better visual prognosis[23].. The appropriate size for a clear corneal incision should be based on the number of RK cuts[24].
Pneumotonometer Accuracy Using Manometric Measurements after Radial Keratotomy, Clear Corneal Incisions and Lamellar Dissection in Porcine Eyes
Published in Current Eye Research, 2020
Lauren A. Maloley, M. Reza Razeghinejad, Shane J. Havens, Vikas Gulati, Shan Fan, Robin High, Deepta A. Ghate
Study intervention comprised of three surgical techniques performed on 28 eyes: radial keratotomy incisions (8 eyes, Figure 2a), lamellar dissection (as in Deep Anterior Lamellar Keratoplasty) (10 eyes, Figure 2b), and clear corneal phacoemulsification incisions (10 eyes). Radial keratotomy was performed using calipers to mark the central corneal 3 mm zone and a circle 0.5–1 mm inside the limbus. Eight radial incisions were created starting at the outer edge of the central 3 mm circle and extending to the inner edge of the outer circle at approximately 2/3 depth of the cornea. To accomplish lamellar dissection, a 2 mm wide incision was made 1 mm anterior and parallel to the limbus with a depth of approximately 2/3 the corneal thickness. Lamellar dissection started at the base of the incision toward the center of the cornea and was completed in all directions using a cyclodialysis spatula. The entry wound was left without suture. Standard, full thickness, phacoemulsification incisions were made with a 2.4 mm incision at the limbal area in addition to a 1 mm side-port incision. All surgical procedures were performed by the same experienced surgeon (MR). All IOPm and IOPp measurements were repeated at each IOP level (10, 20, 30, and 40 mmHg) after performing the 3 corneal procedures described above.
Posterior chamber phakic IOLs vs. LASIK: benefits and complications
Published in Expert Review of Ophthalmology, 2019
Present-day refractive surgery is broadly divided into two types, keratorefractive surgery, in which the shape of the cornea is changed, and phakic intraocular lens surgery, in which a lens is implanted into the eye. Keratorefractive surgery started with the report by Fyodorov et al. on radial keratotomy in 1979 [1]. Then, at the beginning of the 1980s, excimer laser emerged, and in 1990, laser in situ keratomileusis (LASIK) was first reported [2]. Thus, the cornea could be transformed safely and quantitatively by any surgeon, and it became a standard refractive surgery procedure. In contrast, the concept that formed the basis of the phakic intraocular lens (pIOL) was first proposed in the 1950s. In 1986, Fechner et al. reported an iris-supported type, in 1987 Baikoff et al. reported an angle-supported type, and Fyodorov et al. reported a prototype of the posterior chamber pIOL. These three types of pIOLs have respectively advanced and been commercialized; however, the posterior chamber (pIOL) implantable Collamer lens (ICL, STAAR Surgical) is predominantly used. The ICL was developed as IC2020 by STAAR Surgical Inc. in 1993 on the basis of the fundamental study by the Russian group that included Fyodorov. It is a plate-type intraocular lens made from the Collamer copolymer and is transplanted into the posterior chamber, which is the space between the iris and lens. Although good visual function is obtained after surgery with ICL [3,4], it is associated with a risk of postoperative cataract [5]. In 2007, Shimizu [6] developed the Hole ICL (ICL KS-AquaPORT, STAAR), which improved postoperative complications, resulting in a rapid increase in the number of surgeries performed in recent years. The present article compared and reviewed the long-term clinical results, optical properties, and complications of LASIK and ICL, the two standard surgical options.