Peter G. Swann BSc (Hons), MAppSc, FCOptom, FAAO and Katrina L. Schmid BAppSc (Optom) (Hons), GradCertEd (Higher Ed), PhD

Fundus changes in myopiaAn overviewMyopia is the most common of therefractive errors. Due to this, and thefact that many patients have arelatively low degree of myopia, withno deleterious ocular changes, thereis perhaps a tendency to regardmyopia as a simple refractivecondition without considering theserious visual problems which canarise. This article describes thechanges which can occur in theocular fundus due to axial myopia. Atreatment to slow or arrest the axialelongation of the eye and, thus, thesecomplications is required. Band-aidapproaches such as spectacles orrefractive surgery, which do notprevent the elongation of the eye, willhave no beneficial effect in terms ofpreventing such consequences.

The extent to which members of apopulation are myopic varies between races. Inthe United States and other Western countries,about a quarter of the population are myopicby their late teens1 with this figure rising toapproximately one third by 40 years of age.Many people experience a slight decrease intheir level of myopia after about 45 years ofage, most likely due to decreased power of thecrystalline lens2.

The prevalence of myopia is dramaticallyhigher in many Asian races, Jewish and Arabicpeople, and also tends to be more severe. Thereasons for this are not known, with bothgenetic and environmental factors beingsuggested3,4. While approximately one quarterto one third of the myopic population has adegree of myopia greater than six dioptres, theprevalence of severe myopia is likely to behigher in these countries4. It is probable thatthe prevalence and severity of myopia isincreasing worldwide as, therefore, will itspublic health impact5.

Pathological myopia has a prevalence ofabout 2% in the USA and is the seventhleading cause of blindness in that country6.Figures from Canada, albeit somewhat dated,indicated that 9% of blindness was due topathological myopia7.

Pathological myopia usually refers to acondition where there is greater than sixdioptres of myopia or an axial length greaterthan 26-27mm8. It is a progressive, probablyautosomal recessive disorder where seriousocular complications can develop such aschorioretinal degeneration, posteriorstaphyloma, retinal detachment, primary openangle glaucoma and posterior subcapsular andnuclear cataract. Highly myopic eyes also havegreater responsiveness to topicalcorticosteroids and, therefore, there is ahigher risk of raised intraocular pressure (IOP)with their prolonged use9.

Furthermore, other ocular and generalconditions or diseases can be associated withpathological myopia. Some examples includeretinitis pigmentosa, ocular albinism, infantileglaucoma, retinopathy of prematurity, Down’ssyndrome, Marfan’s syndrome, Ehlers-Danlossyndrome and Sticklers syndrome6,10.

FUNDUS CHANGES IN MYOPIA

In this review, we have divided ocular funduschanges in terms of their location, that is, theposterior pole or the fundus periphery. A briefsummary is given in TTaabbllee 11 (page 35).

Blacharski7 divides chorioretinal changes inmyopia into biomechanical, neovascular anddegenerative types. Biomechanical changesinclude the so-called “lacquer cracks”, wherefractures or tears occur in Bruch’s membrane,

and posterior staphylomas. Choroidalneovascularisation can arise, usually in oldermyopes, and resolution may be seen in theform of a Fuchs’ spot. Various degenerativechanges are common such as chorioretinalatrophy, lattice degeneration and pavingstonedegeneration.

POSTERIOR POLE

Optic disc crescentThis is an early change in the myopic fundusand is due to a pulling away of the choroid andpigment epithelium, usually from the temporaledge of the nerve to expose the sclera(FFiigguurree 11). Curtin and Karlin11 found optic disccrescents in all eyes which had an axial lengthof 28.5mm or more. Temporal and annularcrescents predominated. Other studies havefound that the width of the crescent wasstrongly associated with the degree of myopia(FFiigguurree 22).

Research on Chinese subjects in Hong Konghas provided further insights12,13. Whereas theincidence of crescent formation wassignificantly associated with increasing axiallength and myopic refraction, when acquiredrather than physiological crescents wereconsidered, the size of the crescent was notrelated to increased axial length or myopicrefraction. Also, optic discs were morevertically oval in highly myopic eyes – a factorwhich must be considered when examining theoptic disc of a myope who is also a glaucomasuspect, glaucoma being certainly morecommon in myopic eyes, especially the highmyopes14. Appropriate assessment of the opticdisc cup can be a challenge in the myope,particularly when the optic disc is tilted and acrescent or zone of peripapillary atrophy ispresent. In the moderate myope, the cup todisc ratio may be greater than average,whereas the higher myopes may appear to havelittle cup because of posterior staphylomaformation. A stereoscopic evaluation throughdilated pupils is, therefore, mandatory.

Posterior staphylomaA posterior staphyloma is a backward ectasiaof the fundus, the hallmark being tessellationand pallor of the area involved (FFiigguurree 33). Theedges of the staphyloma may be anything butdiscrete. Curtin15 divides staphylomas into fivetypes, with the first, where the area oftessellation and pallor includes the region ofthe optic disc and macula, being the mostcommon. Type two tends to encompass theregion of the macula, type three isperipapillary and type four extends nasallyfrom the optic disc. The fifth type is the mostrare and involves the fundus inferior to theoptic disc. Posterior staphylomas are often

Figure 1Optic disc crescents are common inmyopes. They can vary in size and locationbut are typically situated at the temporaldisc margin as in this three dioptre myope.

Figure 2A much larger crescent in a nine dioptremyope

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progressive and result in vision loss16.Steidl and Pruett17 found that eyes with theshallowest staphylomas showed the largestdrop in visual acuity as well as the greatestfrequency of choroidal neovascular membranesand haemorrhage. They suggested that withless advanced staphylomas, the choriocapillariswas better preserved, thus increasing thelikelihood of the development of neovascularmembranes.

Lacquer cracksLacquer cracks, thought to be healed linearruptures in the retinal pigment epithelium-Bruch’s membrane-choriocapillaris complex18,are present in about 4% of highly myopic eyes19

(FFiigguurree 44). They are frequently seen inconjunction with posterior staphylomas and upto a third can have associated neovascularmembranes. The resolution of any resultanthaemorrhage may lead to the formation of apigmented Fuchs’ spot (FFiigguurree 55). Lacquercracks often progress to form more advancedfundus changes19. Patients with lacquer cracksand/or Fuchs’ spot should receive a guardedprognosis for vision.

Chorioretinal atrophyMore commonly seen in the younger myope,these areas appear as small, punched-outyellow/white lesions in the presence ofposterior staphylomas, and potentially close tolacquer cracks and the macula (FFiigguurree 66). Withtime, smaller lesions frequently coalesce toform larger areas20 (FFiigguurree 77). Chorioretinalatrophy may be the result of stretching andthinning of the retinal pigment epithelium andchoroid as the eye enlarges, thus exposing thesclera21.

FUNDUS PERIPHERY

The major threat to vision in the myopic eye isretinal detachment, especially as posteriorvitreous detachment (PVD) and predisposingretinal degenerations, such as latticedegeneration, are more common in these eyes.

Akiba22 suggested that in high myopia, PVDdevelops increasingly with age and the degreeof myopia, and that it may be seen as much as10 years earlier in highly myopic eyescompared to emmetropic eyes. In a study of218 patients with myopia of six dioptres ormore in both eyes, Celorio and Pruett23 foundthat one third had lattice degeneration, withthe greatest prevalence being in eyes havingsix to nine dioptres of myopia. Latticedegeneration represents vulnerable areas ofretinal thinning. It is non-age specific and isseen in about 40% of eyes with retinaldetachment9.

Pigmentary degeneration, consisting ofextensive pigment deposition in the extremeretinal periphery, and the non-predisposingpaving stone degeneration (yellow-white areasof chorioretinal thinning) are also morecommon in myopic eyes. The pigmentproliferation and RPE migration of pigmentarydegeneration may be due to retinal traction,while the chorioretinal thinning in pavingstone degeneration may be due to localisedocclusion of the choroidal circulation16. Whitewithout pressure (translucent whitish

circumferential patches), from a prominentvitreous base and mild vitreous traction, ismore frequently seen in myopic eyes andoccasionally retinal breaks can occur in thepresence of such lesions9,16.

It has been estimated that potentially up to80% of eyes suffering retinal detachment havesome degree of myopia. Also, a person withfive dioptres of myopia is at a 15 times greaterrisk of developing retinal detachment than anemmetrope. With 20 dioptres of myopia, therisk increases to 110 times7. There are alsoreports of retinal detachments in myopesfollowing clear lens extraction procedures usedto refractively correct the myopia24.

MANAGEMENT

Myopic patients, especially those withpathological myopia, must be reviewedregularly, preferably on an annual basis, andalways through dilated pupils. They shouldreceive appropriate warnings of signsand symptoms that may indicate asight-threatening situation is developing,and be advised to utilise protective eyewear in

Figure 3The most common type 1 posteriorstaphyloma. The edge of thestaphylomatous region is arrowed

Figure 4Lacquer cracks near the macula

Figure 5A developing Fuchs’ spot together withhaemorrhage and a serous detachment ofthe macula. Vision was markedly reduced

Figure 6Chorioretinal atrophy: small, punched outlesions near the macula (the white streak atthe bottom of the photograph is artefact)

Figure 7Chorioretinal atrophy: larger geographicareas involving the posterior pole

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March 22, 2002 OT34 www.optometry.co.uk

potentially hazardous circumstances. Patientsat risk for subretinal neovascular membraneformation should be given a take-home Amslergrid for daily testing. The increased incidenceof associated conditions, such as glaucoma,must be remembered.

About the authorsPeter Swann is Associate Professor andKatrina Schmid Senior Lecturer in the Schoolof Optometry, Queensland University ofTechnology, Brisbane, Australia. ProfessorSwann has a particular interest in eye disease,and Dr Schmid in the aetiology of myopia.

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3. Wu MM, Edwards MH. (1999) The effect ofhaving myopic parents: an analysis ofmyopia in three generations. Optom. Vis.Sci. 76: 387-392.

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myopia: implications for Australia.Clin. Exp. Ophthalmol. 29: 116-120.

6. Alexander LJ. (1994) Primary care of theposterior segment. Appleton & Lange,Connecticut.

7. Blacharski PA. (1988) Pathologicprogressive myopia, in DA Newsome Ed.,Retinal dystrophies and degenerations.Raven Press, New York.

8. Miller DG, Singerman LJ. (2001) Naturalhistory of choroidal neovascularization inhigh myopia. Curr. Opinion Ophthalmol.12: 222-224.

9. Kanski JJ. (1994) Clinical Ophthalmology3rd ed, Butterworth-Heinemann, Oxford.

10. Marr JE, Halliwell-Ewen J, Fisher B et al.(2001) Associations of high myopia inchildhood. Eye 15: 70-74.

11. Curtin BJ, Karlin DB. (1971) Axial lengthmeasurements and fundus changes of themyopic eye. Am. J. Ophthalmol. 71: 42-53.

12. Hendicott P, Lam C. (1991) Myopiccrescent, refractive error and axial lengthin Chinese eyes. Clin. Exp. Optom. 74: 168-174.

13. Lam AKC, Cheng KKH, Lam RK et al. (1996)Optic disc ovalness, refractive error andaxial length of Hong Kong Chinese.Clin. Exp. Optom. 79: 167-172.

14. Mitchell P, Hourihan F, Sandbach J, WangJJ. (2000) The relationship betweenglaucoma and myopia. Ophthalmology 106:2010-2015.

15. Curtin BJ. (1977) The posterior staphylomaof pathologic myopia.

Trans. Am. Ophthalmol. Soc. 75: 67-86.16. Hoffman DJ, Heath DA. (1987) Staphyloma

and other risk factors in axial myopia.J. Am. Optom. Assoc. 58: 907-913.

17. Steidl SM, Pruet RC. (1997) Macularcomplications associated with posteriorstaphyloma. Am. J. Ophthalmol. 123:181-187.

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19. Ohno-Matsui K, Tokoro T. (1996) Theprogression of lacquer cracks in pathologicmyopia. Retina 16: 29-37.

20. Ito-Ohara M, Seko Y, Morita H et al. (1998)Clinical course of newly developed orprogressive patchy chorioretinal atrophy inpathological myopia. Ophthalmologica212: 23-29.

21. Morse PH. (1989) Vitreoretinal disease 2nded, Year Book Medical Publishers, Chicago.

22. Akiba J. (1993) Prevalence of posteriorvitreous detachment in high myopia.Ophthalmology 100: 1384-1388.

23. Celorio JM, Pruett RC. (1991) Prevalence oflattice degeneration and its relation toaxial length in severe myopia.Am. J. Ophthalmol. 111: 20-23.

24. Ripandelli G, Billi B, Fedeli S. (1996)Retinal detachment after clear lensextraction in 41 eyes with high axialmyopia. Retina 16: 3-6.

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Table 1 Summary of potential ocular fundus changes in high myopia

FUNDUS CHANGE

Optic disccrescent

Posteriorstaphyloma

Lacquer cracks

Chorioretinalatrophy

Fuchs’ spot

Latticedegeneration

Pigmentarydegeneration

Paving stonedegeneration

White withoutpressure

LOCATION

Posterior pole

Posterior pole

Posterior pole

Posterior pole

Macula

Periphery

Periphery

Periphery

Periphery

AETIOLOGY

Biomechanical

Biomechanical

Biomechanical

Degenerative

Neovascular

Degenerative

Degenerative

Degenerative

Biomechanical

PREVALENCE

Observed in most myopes,100% of eyes with axial length≥28.5mm11

Observed in 76% of myopes,-3 to -38D16

Observed in 4% of highmyopes >6D19

Observed more commonly inyounger high myopes, 23% ofmyopic eyes with axial length>24.5mm11

Observed in 5-10% of eyeswith axial length ≥26.5mm11

Observed in 13-30% ofmyopes23,25

Observed in 17% of myopes25

Observed in 27% of myopes25

Observed in 23% of myopes25

EFFECT ON VISION

None, unless other pathologyalso present

Can be progressive and resultin vision loss

Guarded prognosis for vision

Guarded prognosis for visionif at the macula

Guarded prognosis for vision

None, unless secondarypathology occurs

None

None

None, unless secondarypathology occurs

MAY LEAD TO

----

Choroidal neovascularmembranes

Choroidal neovascularmembranes

Associated with posteriorstaphylomas, lacquer cracks

Associated with posteriorstaphylomas, lacquer cracks

Retinal detachment

----

----

Occasionally retinal tears

Prevalence values should only be used as an indication of how common these changes are in the myopic eye.Reported prevalence values vary greatly between studies, due to differences in the age of subjects and severity of the myopia.

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