Advances in the research of high myopia treatment

Ming-Shan LiuYa Mo

1Chengdu University of Traditional Chinese Medicine,Chengdu,Sichuan province,China.2Teaching Hospital of Chengdu University of Traditional Chinese Medicine,Chengdu,Sichuan province,China.

Abstract High myopia,is a condition of the diopter over-6.00D,accompanied by axial extension and fundus changes,such as temporal arc plaque,pigment epithelium thinning,leopard-shaped fundus,fuchs spot,retina choroidal atrophy,progressive decline in vision,as well as amblyopia,glaucoma,cataract,vitreous opacity,retinal detachment and other ophthalmic diseases.High myopia is one of the common causes of blindness in China.It is necessary to review these cases in order to better guide the clinical and improve the level of vision of patients.

Key words:High myopia,Present status of treatment,Progress

Introduction

The incidence rate of high myopia is 1%,and in the elder people of Asia,the prevalence rate is 1%-5%[1].At present,clinical treatments for high myopia are various.Current non-surgical methods such as glasses,soft contact lens and rigid gas permeable contact lens(RGP)are the most widely used for correction of high myopia.Surgical treatment is the highlight of current researches,including mature surgical excimer laser corneal surgeries such as excimer laser-in-situ keratomileusis(LASIK),epipolos-laser in situ keratomileusis(Epi-LASIK)and sub-bowman's keratomileusis(SBK).Intraocular lens implantation in phakic eye(ICL),posterior scleral reinforcement(PSR)is the new hot issues.This article will review these methods and their advantages and disadvantages as well.

Non-surgical refractive treatment for high myopia

Frame glasses

Frame glasses can enlarge or reduce the retinal image,which leads to the eyes present unequal size image,not easy or cannot be integrated,or the small field of vision and other unique optical defects.It is always difficult to obtain good corrected visual acuity and visual effect.What’s more,in order to get self-comfort after wearing frame glasses,patients have to reduce the degree of correction of myopia.Some patients even give up wearing glasses[2].

Corneal contact lenses

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Data specification

Corneal contact lenses are divided into soft and hard lenses.For the lack of oxygen permeability,wearing soft corneal contact lens can easily lead to complications such as dry eyes and corneal vascularization.It is difficult to achieve and maintain a good correction vision.RGP is a new kind of contact lens in recent years.This kind of vision correction technique utilizes the high oxygen permeability,dynamic sliding design of the material and the good opticalproperties and correctness.Itsolves the refractive problem,butalso solves the oxygen permeability problem.The patient's retina image can be clearly presented in the height and ultra-high refractive error amblyopia.RGP is wore on the corneal surface to form a new optical system of lens-tear film-cornea,which effectively eliminates corneal surface astigmatism,significantly reduces aberrations,improves retinal imaging quality,and achieves better visual effects[3-7].

Treatment of high myopia with refractive surgery

Excimer laser corneal refractive surgery LASIK

LASIK uses micro-corneal knife to do lamellar corneal flap,and then uses excimer laser in the corneal stroma bed for refractive that retains the corneal epithelium and the front elastic layer of the cornea integrity.It is widely welcomed because of its advantages such as rapid wound healing,rapid recovery of vision,almost no corneal opacity,and no need long-time using hormones postoperative with big range of refractive correction and the small refractive regression.LASIK has a high predictability and stability.Excimer laser surgery is the most effective and safe method for correcting ametropia in the world today[8,9].With the of excimer laser corneal refractive surgery carried out,the occurrence of complications are also increasing.LASIK has common postoperative complications such as glare,diopter subtractive or overcorrection,corneal flap shifted,corticosteroid high intraocular pressure,retinaldetachmentand acute conjunctivitis,but complications are in a high control,that based giving timely symptomatic treatment to an occurrence of complications,to ensure the vision of the patients.[10-12].

Epi-LASIK

Epi-LASIK isactually aLASEK surgery with mechanical flap method.Intraoperative application of a high-speed concussion plastic"blunt knife"separation of the corneal epithelium,makes a complete,pedicled corneal flap,and then completes the laser cutting and reduction of the flap.Epi-LASIK has no LASIK corneal stromal valve-related complications,and is much safer,and retains a thicker bed.Also the risk of secondary corneal dilatation is lower than that of LASIK.At the same time,it avoids the occurrence of new aberration due to the production of corneal stromal flap.Epi-LASIK treatment for high myopia is safe and effective.It broadens the range of correction of corneal refractive surgery,so that the surgeons have more choices and it brings new method to refractive error correction of vision.It combines the advantages between PRK and LASIK,and it is a new technology with great potential for development[13,14].Using mitomycin C(MMC)during Epi-LASIK can significantly inhibit the formation of corneal haze(Haze)with easily operation and make vision stable with non-toxic side effects[5,6].But its long-term clinical efficacy still needs more cases and longer time to follow-up and research.

Sub-bowman's keratomileusis

SBK is developed on the basis of traditional LASIK,which makes corneal flap on the desement membrane.It uses disposable fiber corneal knife to make an ultra-thin flap whose thickness is about 90-110μm,and does the laser cutting on the desement membrane,retaining a complete pre-elastic layer without loss of deeper fibers and the maximum retention of the biomechanics of the cornea.The manufacture of ultra-thin corneal flap makes SBK remain more cornealstroma than traditionalLASIK surgery preventing post-LASIK keratectasia and iatrogenic keratoconus,and expand the intended population for the operation,so that it can improve the quality of life of patients with high myopia[15,16].Although a small number of patients after surgery will have glare,dry eyes and other uncomfortable symptoms,but the vast majority of patients who had the SBK achieved a higher visual quality.In the future,with the organic connection between aberration instrument analysis system and the excimer laser machine treatment system,according to the patient's diopter,pupil diameter,corneal thickness and other parameters to design a personalized surgery promotion,SBK will make more myopia patients get more fine visual imaging capabilities and better visual quality[17,18].

ICL Posterior chamber ICLimplantation

ICL implantation implants intraocular lens with the type of posterior chamber’s in the ciliary sulcus,and its range of the refractive errors treatment is quite large.Also it is not limited by the corneal thickness.Thus it can retain the regulation of the natural lens function,reducing the damage to the corneal endothelial cells.After correction,vision is much clearer,so it becomes the preferred treatment in current clinical treatment of height Myopia and even ultra-high Myopia.It appears to be a reliable way to cure high myopia or ultra-high myopia which makes people focus on it[19,20].

Postoperative high intraocular pressure is a common complication after the operation,and there may be some reasons for high intraocular pressure:pupil block,viscoelastic agent,hormone drug application,inflammatory response,too large ICL diameter and so on.Therefore,preoperative corneal transverse diameter measurement,intraoperative use of easy-removed low molecular weight viscoelastic,postoperative intraocular pressure,angle examination,lens anterior capsule and intraocular lens spacing measurement are all very important[21,22].

Anterior chamber ICL implantation

Anterior chamber ICL is divided into two types of fixed angle and iris clip fixation.A large number of foreign studies have shown that the postoperative efficacy of iris fixed ICL implantation is affirmed.Its refractive state is stable,without fluctuations.It is a safe,effective,accurate and stable correction of high myopia refractive surgery[23].

The drop of corneal endothelial cell is the main complication of anterior chamber ICL implantation,and severe cases need to remove the intraocular lens.The reasons why corneal endothelium reduces are considered as the following points:(1)intraoperative corneal endothelium injury,which occurs more often in the implantation of intraocular lens and adjusting the fixed intraocular lens.(2)Intraocular lens contacts with corneal endothelium.(3)Intraocular inflammation injures the corneal endothelium is another factor that worth to focus on.With the development of intraocular lens materials,the improvement of intraocular lens design and the improvement of surgical quality,the operation will be more perfect[24,25].

PSR

PSR places a certain amount of reinforcement on the weak portion in the posterior pole sclera of the high myopia.It mechanically reinforces the sclera,thereby preventing eyeball dilatation and axial growth,and inhibiting the progress of high myopia,also can shorten the axial,reduce the diopter,and improve vision.

Early postoperative symptoms include conjunctival hyperemia,edema,eye fasciitis,foreign body sensation(individualpatients),tears,photophobia,transient diplopia,mild headache nausea and so on.They disappeared within 1 week.It is rare to find visual dark spots,uveitis,retinal detachment and other serious complications.Now,PSR is mainly used for the rapidly developed treatment of advanced high myopia patients and associated with macular degeneration opatientswith ultra-high myopia.Some scholars believe that patients with high myopia and concurrent retinal detachment have retinal detachment surgery while at the same time surgeons should also consider posteriorscleralreinforcementsurgery.With the extensive application and development of clinical and scientific research,posterior scleral reinforcement can achieve greater improvement and wider application,as much as possible to improve and protect the visual function of patients with high myopia.

Summary and Prospect

Because most patients with refractive errors can get a good refractive correction through the glasses and contact lenses and other non-surgical methods,so their expectations on refractive surgery are very high.When we correct high myopia patients,we should not only consider the correction of intraoperative refraction,but also should consider the stability of postoperative uncorrected visual acuity,eye safety.In addition,we should also strictly know the surgical indications,make preoperative patients fully understand the possible results of surgery and risk,try to avoid complications.In short,with the continuous emergence of new technology and new equipment,through improved laser cutting mode,we improve the surgical approach and flap production approach,and make standards of surgical operation.We make personalized treatment program,and strive to improve the quality of surgery to meet the growing quality of vision that patient’s demand,which will be the future trend of development of refractive surgery