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Degenerative myopia is one of the leading causes of visual impairment in the world occupying the seventh position in the United States and Europe1. It is the first cause of visual impairment in Japan2. It is defined as a refractive error greater than -6.00 diopters and an axial length of more than 26 millimeters. The average rate of this condition is 1.7 to 2.1 percent worldwide but can reach up to 10 percent in certain areas of Asia.3

The condition is known to be linked to environmental, genetic, and socioeconomic risk factors. Studies performed in Singapore showed that higher levels of education, better housing, higher individual monthly income, and occupations requiring extensive near work increased the prevalence of myopia4.

The pathophysiology of Degenerative myopia begins with progressive anteroposterior elongation of the sclera with or without staphylomas (outpouching of the globe)5. As the stretching of the globe occurs, hypoplasia and scattering of the retinal pigment epithelium (RPE) allows for the choroidal vessels to be more visible and is called Tessellated fundus. Tessellated fundus is typically associated with a crescent corresponding to an exposed area of the sclera that comes in contact with the papillary edges. Cupping of optic nerves with high myopia has the tendency to contract temporally which makes it difficult when assessing glaucomatous nerve damage6. Axial length elongation is also thought to be responsible for causing choroidal thinning called Lepto Choroid and is defined as a choroidal thickness of less than 20 microns in the subfoveal zone. As the degenerative process progresses, a multitude of secondary ocular changes occurs principally thought to be due to mechanical stretching and involve the posterior pole, the peripheral retina, the vitreous, and the crystalline lens.

Macular changes associated with pathological myopia:

Posterior Staphyloma

Macular Hole 

Foveal Retinoschisis

Lacquer cracks

Macular Subretinal hemorrhage

Choroidal Neovascularization

Fuch spots 

The hallmark of degenerative myopia is posterior staphyloma. It is an ectasia of the posterior sclera due to thinning and focal expansion and is best appreciated on A, B-scan ultrasound, or MRI. Further disease processes occurring in the posterior pole include macular hole, foveal retinoschisis, Fuchs spot, Lacquer cracks, subretinal hemorrhages, and choroidal neovascularization. Subretinal hemorrhages sometimes called “coin” hemorrhages may be intermittent and occur from choroidal neovascularization or secondary to posterior staphyloma causing bleeding from the choriocapillaris and often coincides with lacquer cracks8. Fuchs spot is an elevated, circular, pigmented lesion at the macula occurring after a subretinal hemorrhage has been absorbed or as a choroidal neovascularization regresses leaving a subfoveal fibrous pigmented scar8. Lacquer cracks are ruptures in the RPE-Bruch membrane-choriocapillaris complex seen as fine yellow lines radiating most often from the macular area and crisscrossing at the posterior pole. They are present in about 5 percent of high myopes and can precede the apparition of choroidal neovascularization, subretinal hemorrhages, and geographic atrophy5. It is thought that the disruption of the RPE-Bruch membrane-choriocapillaris complex allows entry of new choroidal neovascularization to the subfoveal area.

Macular CNV is one of the most vision-threatening complications of degenerative myopia with an incidence of 5 to 10 percent in highly myopic patients and occurs most commonly in association with lacquer cracks or chorioretinal atrophy. Older patients seem to have a poorer prognosis regarding choroidal neovascularization as the involved area tends to be smaller and shallower in younger patients5. Type 2 neovascularization (CNV above the RPE) is the most common manifestation of proliferation disease in myopic macular degeneration8. 

SS-OCT shows a type 2 CNV with minimal subretinal exudation, a very thin choroid, and shisis-like changes on the left hand of the scan.

Typically, myopic CNV is a small, flat, greyish, subretinal membrane that is less than 1 disc diameter in size12 and is located between the neurosensory retina and retinal pigment epithelium (RPE) (type 2).13 Whereas the CNV secondary to age-related macular degeneration (AMD) is usually in the sub-RPE space (type 1). Most myopic CNV is subfoveal or juxtafoveal with minimal subretinal fluid or exudate.12

Myopic CNV tends to have a classic pattern of leakage on fluorescein angiography (FA) and appears as a plaque-like elevation with pigmented halo and sharply defined borders. 

In contrast to age-related macular degeneration, CNV lesions in pathological myopia may remain stable without affecting vision if left untreated7. Over the last decade, intravitreal injection of anti-VEGF has become the first-line treatment for CNV showing promising results. The stability of CNV in patients with degenerative myopia may allow a lower frequency of injections to achieve stability when compared to AMD patients. Clinicians should be aware that anti-VEGF injections represent an off-label use of the medication in these patients. Today, laser photocoagulation is used as second-line therapy for CNV. A study showed that although initially beneficial, laser photocoagulation loses its benefit after 5 years due to high rates of CNV recurrences10.

In many cases, CNV recurrences occurred at the margins of the previously treated zones suggesting the disruptive nature of laser photocoagulation to the RPE-Bruch’s complex. Furthermore, additional lacquer cracks were also reported following treatment. Because of the before-mentioned complications, Photodynamic therapy (PDT) emerged as a safer treatment for myopic CNV. According to the Verteporfin in Photodynamic Therapy (VIP) study, 64 percent of treated eyes lost fewer than 8 letters during the first 2 years of treatment. When looking at long-term results, a retrospective study performed on 43 eyes found that visual acuity was stable during the first year following PDT but worsened during the second year, and nearly 3 lines of acuity were lost at the seventh’s year follow-up. Macular chorioretinal atrophy occurred in 83% of patients at the five-year mark11.

Foveal retinoschisis, sometimes mistaken for cystoid macular edema, may occur in conjunction with posterior staphyloma and is thought to be resulting from vitreal traction on a weakened retina. Patients with degenerative myopia may suffer from a macular hole that occurs spontaneously or following mild trauma and is associated with a much higher prevalence of retinal detachment compared to age-related idiopathic macular hole. Macular hole is the leading cause of severely reduced visual acuity in patients with degenerative myopia. Similarly to foveal retinoschisis, staphylomas and posterior vitreous detachment are predisposing factors for macular holes5. Peripapillary detachment (PDPM) is a relatively new type of lesion recognized in highly myopic patients. It is defined as an asymptomatic, yellow-orange peripapillary detachment of the retinal pigment epithelium and retina in pathological myopia. A study performed in 2003 followed 15 patients with PDPM during a 6-year period and concluded that PDPM lesions all remained stable except for 1 patient, and no apparent negative visual function was noted9.

Yellow-orange lesion in the periphery of the myopic crescent (black arrows). OCT shows a longitudinal scan of the same patient which clearly identifies hollow spaces adjacent to the disc.

Peripheral signs of high myopia often include lattice degeneration, pavingstone degeneration, snail track degeneration, and atrophic holes, all of which represent thinning of the retina and can sometimes lead to further complications such as retinal breaks and retinal detachments. The pathogenesis of rhegmatogenous retinal detachment is thought to be related to the before-mentioned thinning of the peripheral retina, early onset posterior vitreous detachment, atrophic holes, and macular holes. The severity of myopia seems to be related to the prevalence of retinal detachments.

Differential diagnosis of degenerative myopia may include Serpiginous Choroiditis or Presumed ocular histoplasmosis syndrome due to their patchy chorioretinal atrophic spots within the posterior pole and potential for CNV; however, a history of progressive high and increasing myopia should direct your diagnosis to a myopic etiology.

Diagnostic modalities

Common diagnostic modalities used in the assessment of the macula for pathological myopia include fundus photography, Macular OCT and OCT-A, Fundus autofluorescence, fluorescéine angiography, and visual field. OCT is an important tool used in these patients and should be performed periodically on high/pathological myopes to rule out macular conditions, such as CNV. In case of suspicion for CNV, an OCT-A or FA should be performed. Lastly, FAF is useful in evaluating the area of functional retina available within the posterior pole (see below). 

Important Takeaways: 

  • Degenerative myopia is one of the leading causes of visual impairment in the world occupying the seventh position in the United States and Europe. It is the first cause of visual impairment in Japan.
  • The pathophysiology of Degenerative myopia is caused by progressive anteroposterior elongation of the globe which leads to pathology of the posterior pole and peripheral retina. 
  • The hallmark of degenerative myopia is posterior staphyloma however, the 2 most important causes of significant reduction in visual acuity are macular hole and CNV. 
  • OCT is critical especially given the atrophic appearance of the posterior pole in patients with degenerative myopia in order to rule out CNV and macular hole. 
  • In contrast to age-related macular degeneration, CNV lesions in pathological myopia may remain stable without affecting vision if left untreated. The stability of CNV in patients with degenerative myopia may allow a lower frequency of injections to achieve stability when compared to AMD patients. 
  • Evaluation of the peripheral retina is especially important in high myopes in order to rule out retinal holes and breaks which can lead to a retinal detachment. The severity of myopia seems to be related to the prevalence of retinal detachments.

 

References:

1. Ryan S.J et al. Retina. 5th edition. Philadelphia: Elsevier; 2012:1115-1133.

2. Hayashi K et al. Ophthalmology. 2010; 117(8):1595-1611.

3. Freund B.K, Sarraf D, Mieler W.F, Yanuzzi L.A. (2017). The Retinal Atlas. 2: 674.

4. Wong T.Y, Foster P.J, Johnson G.J, Seah S.K. Refractive errors, axial ocular dimensions, and age-related cataracts: the Tanjong Pagar survey. Invest Ophthalmol Vis Sci. 2003;44 (4:1479–1485.

5. Kanski J.J, Bowling B, Nischal K, Pearson A. (2011). Clinical Ophthalmology: A Systematic Approach. 7: 642.

6. Tokoro T. (1998). Atlas of Posterior Fundus Changes in Pathologic Myopia.1:6.

7. Fineman M.S, Ho A.C. (2012). Color Atlas & Synopsis of Clinical Ophthalmology, Wills Eye Institute, Retina. 2:67-68.

8. Freund B.K, Sarraf D, Mieler W.F, Yanuzzi L.A. (2017). The Retinal Atlas. 2: 689-690.

9. Freund KB, Ciardella AP, Yannuzzi LA, et al. Peripapillary Detachment in Pathologic Myopia. Arch Ophthalmol. 2003;121(2):197–204. doi:10.1001/archopht.121.2.197.

10. Soubrane G et al. Bull Soc Ophtalmol Fr. 1986;86(3):269-272.

11. Giansanti F et al. Retina. 2012;32(8):15471552.

12. Hampton GR, Kohen D, Bird AC. Visual prognosis of disciform degeneration in myopia. Ophthalmology 1983;90:923–6.

13. Hotchkiss ML, Fine SL. Pathological myopia and choroidal neovascularization. Am J Ophthalmol 1981;91:177–83. 

Stephane Fitoussi
Stéphane Fitoussi, OD is originally from Paris, France and earned his Bachelor of Optometry in Israel. He achieved his Doctorate of Optometry at Nova Southeastern University in Florida and his residency in Ocular disease at the Bascom Palmer Eye Institute in Miami. He is the creator and manager of Interesting Retinal Cases where retinal content is posted through interesting educational images and real-life cases.

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