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Introduction

High myopia or pathological myopia is associatedwith globe elongation and a refractive error of at least6 diopters (D) and/or axial length of greater than 25.5

mm .1- 3

T he p r eva le n ce o f h i gh m y op i a va r ie sconsiderably in different ethnic groups and has beenestimated to be around 10% in Asian populations.1,2

Excessive axial elongation of the globe in high myopiacan cause mechanical stretching and thinning of thechoroid and retinal pigment epithelium layers,resulting in various retinal degenerative changes.4 It iswell known that individuals with high myopia haveincreased risks of retinal complications such asperipheral retinal degenerations, retinal tears, retinaldetachment, posterior staphyloma, chorioretinalatrophy, retinal pigment epithelial atrophy, lacquercracks, choroidal neovascularisation (CNV) andmacular haemorrhage.4- 6 In a cr o s s- s e ct i o na lcommunity-based epidemiological study in HongKong, 56.1% and 11.3% of subjects with high myopia

were found to have one or more peripheral retinald eg en e ra t iv e l e si o n o r p o st er i or p o le l e si o nrespectively.7 Some of these retinal lesions may beassociated with severe irreversible visual loss andtherefore it is important for clinicians to be aware ofthe retinal pathologies in high myopia. This reviewaims to provide an overview on some of the importantretinal complications associated with high myopia.

Peripheral retinal degenerations andrhegmatogenous retinal detachment

Epidemiological studies have demonstrated increasedprevalence of peripheral retinal degenerations in

association with high myopia and increased axiallength.4-13 Among the different types of peripheralr e ti n al d e ge n er a ti o ns i n h i gh m y op i a, l a tt i cedegeneration is the most important peripheral retinaldegeneration which can predispose to rhegmatogenousretinal detachment (RRD).14 This is because retinal tearscan develop at the posterior and lateral margins of thelattice degeneration caused by strong vitreoretinaladhesions following posterior vitreous detachment.Symptoms of posterior vitreous detachment and retinalbreak formation include sudden or gradual increase inthe number of floaters and/or flashes. In patients withRRD, they may also develop symptoms of curtain-likeprogressive visual field loss and blurring of vision.Dilated fundus examination should be carried out inpatients with these symptoms as soon as possible to

detect for the development of retinal break or retinaldetachment.

Laser photocoagulation is used for the treatment of eyeswhich have developed retinal hole or break. This can beperformed in the majority of patients under topicalanaesthesia as an out-patient procedure. Several rows oflaser are applied onto the retina to surround the retinal

defect in order to seal off the retinal break (Fig. 1). Sincearound 30% of eyes with acute RRD have been found tohave lattice degeneration, prophylactic laser treatmentcan also be performed in patients with peripheral retinaldegenerations,15 especially those with a history of retinaldetachment in the fellow eye.

In eyes with retinal detachment, laser photocoagulationalone is insufficient to treat the condition andvitreoretinal surgery is required. Surgical modalities forRRD include pneumatic retinopexy, scleral bucklingsurgery with cryopexy, and pars plana vitrectomy withintravitreal tamponade such as gas or silicon oil. The goalof the surgery is to identify and seal off all retinal breaks.For patients in whom the macula is still attached, theywill generally have favourable visual outcomepostoperatively. However, for patients in which thecentral of the macula i.e. the fovea is detached, the visualprognosis of the patient is more variable and somepatients might develop irreversible visual loss despitesuccessful retinal detachment surgery. Therefore, promptophthalmic consultation is advised for early detection ofretinal detachment in order to prevent irreversible visualloss.

Myopic foveoschisis and macular hole

Due to excessive axial elongation of the globe in highmyopia, patients candevelop posterior bulgingor ectasia

Retinal Complications of High Myopia

Dr.TimothyYYLai

Dr. Timothy YY Lai

MBBS, MMedSc, MRCSEd, FCOphthHK, FHKAM(Ophthalmology)

Associate Professor, Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong

Figure 1. Retinal hole surrounded by fresh laser photocoagulationmarks in a patient with high myopia

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Conclusions

Individuals with high myopia are subject to variousretinal pathologies including peripheral retinal

degenerations, retinal detachment, and posterior polechorioretinal lesions. Since these retinal pathologiesmight be associated with serious sight-threateningcomplications, patients with high myopia should beeducated about the symptoms of retinal complicationssuch as retinal detachment, macular hole, and myopicCNV. Patients should be advised to seek medical carepromptly should such symptoms arise. Prompt referralto ophthalmologists will be useful in preventing severevisual loss as effective surgical and medical treatmentsare available for these retinal complications especially inthe early stages.

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