Second Prize: ICG Angiography Helps Diagnose Pathological Myopia
Leigh Anne Green, Robyn G. Kralich, O.D., Houston

A 42-year-old white male presented complaining of a gradual increase in blur at distance and near, especially in the left eye. His ocular history revealed long-standing flashes, floaters and photophobia. He wore corrective lenses since age 4, with his prescription increasing yearly.

Top: The fundus appearance of the right eye. The manifest refraction was –19.00 –1.50 x 010. Middle: The fundus appearance of the left eye. The manifest refraction was –22.00 –3.50 x 160. Bottom: The appearance of the macular region of the left eye.

His medical history was positive for hypertension and hypercholesterolemia, for which he was taking verapamil, metoprolol and atorvastatin. His family history was negative for degenerative myopia.

Diagnostic Data
Entering acuities through his current spectacles were -18.25 -1.50 x 010, 20/30 O.D. and -18.75 -3.50 x 160, 20/80 O.S. Phoropter and loose-lens refraction brought the patient to 20/30 O.D. and 20/40 O.S., but this required an increase of -0.75 to the right eye sphere and -3.25 to the left eye sphere. The addition of +1.50 to both eyes resulted in near acuity of 20/40. The pupils, extraocular muscles and confrontation fields were unremarkable.

Biomicroscopy of the anterior chamber was unremarkable in both eyes. The crystalline lenses showed posterior cortical cataracts grade 2+, along with bilateral posterior vitreous detachment. Goldmann pressures were 14mm Hg O.U.

The dilated fundus exam revealed overall thinned and stretched retinas, appearing pale and mottled in color. The scleral shell lent a yellowish color to the fundus through the thinned retina and choroid. The discs were hypoplastic and tilted along the vertical axis. The retina surrounding the discs was thinned, pulled away from the disc margins and apparently atrophic. C/D ratios were indistinct because of the anatomical distortions in and around the discs.

The maculae appeared free of drusen, hemorrhages, edema or scarring. The left eye showed a disruption in the retinal pigment epithelium slightly nasal to the fovea. The peripheries of both eyes had a similar appearance of cobblestone degeneration 360°. There were no retinal detachments, holes or breaks.

Diagnosis
We had diagnosed pathological myopia O.U. Our plan was to issue a new spectacle prescription and schedule a follow-up visit for indocyanine green angiography and B-scan ultrasonography.

ICGA revealed atrophy from the nerve to the macula, but no hyperfluorescent neovascular membranes were visible at the suspicious RPE disruption in the left eye. The axial length on B-scan measured 32.5mm O.D. and 34.0mm O.S. We recommended the patient get a dilated exam annually, and scheduled him for a contact lens fitting. 

Top: In the early phase of indocyanine green angiography of the left eye, the ICG dye is contained in the retinal and choroidal vasculature. Middle: In the middle phase the dye stays in the choroidal vasculature only. Bottom: In the late phase the infrared filter only fluoresces the dye for observation, so fundus features are indistinct.

The contact lens fitting was successful. Corneas measured 43.00/ 44.87@180° O.D. and 41.37/ 44.25@170° O.S. Boston EO bitoric RGPs provided adequate movement and centration on both eyes: 8.15/7.90 //-12.75/-14.00, 20/20- O.D.; and 8.10/7.70 //-15.00/ -17.00, 20/40 O.S. The patient was pleased with the magnification and the improved cosmesis with the contact lenses. He is scheduled to return in one year unless he notices any change in vision. We also suggested home Amsler grid monitoring to detect any central distortions.

Discussion
Pathological, or degenerative, myopia affects only 2% of Americans yet is the nation's seventh leading cause of blindness.1,2 The disease process results in a progressive globe elongation, creating stress on the choroidal tissues and vasculature.1,3 A. Sahap Kukner and associates defined pathological myopia as an objective refraction greater than -6.00D, an axial length greater than 26mm and at least one of the common fundus changes: temporal conus around the nerve head, posterior staphyloma, thinned RPE and choroid, or peripheral retinal degeneration.4 Besides ruling out retinal breaks and detachments, carefully evaluate the patient for chorioretinal atrophy, lacquer cracks and neovascular membranes.1,2,5 

Some 30% of patients exhibit signs of myopic degeneration at birth, while 60% present with signs from ages 6-12. This disorder seems to be predominant among Chinese, Japanese, Arabic and Jewish patients, but is not directly linked to gender.3,5 The disease progresses with age due to scleral thinning and posterior pole ectasia as the axial length increases.3 The most common pathological change, found in just about all patients, is a myopic conus around the nerve head due to retinal thinning.2,5 Peripheral retinal changes most commonly present as cobblestone degeneration, seen in 14% to 27% of older patients.2 Other peripheral changes include lattice degeneration and atrophic and operculated holes.3
Chorioretinal alterations begin when the mechanical strain on the vasculature becomes too great. This challenges the choriocapillaris structure, and breaks may develop in Bruch's membrane.3 These breaks typically cause subretinal bleeding which can absorb with little or no effect on vision.

About four months after the break, scarring and atrophy of the overlying RPE may appear as a yellowish, linear lesion on ophthalmoscopy.6 Known as lacquer cracks, these healed breaks in the RPE-Bruch's membrane complex occur in 4.3% of highly myopic eyes.2,5,7 Lacquer cracks often appear early in the disease, but their primary importance is prognostic.8 Once a passage forms from the choroid into the retina, neovascular membranes have a better chance of penetrating the blood-retina barrier. As a result, choroidal neovascularization develops in 5-10% of pathologically myopic patients, creating visual impairment as the neovascular membranes lead to retinal and subretinal hemorrhages.9

A Fuch's spot represents an end-stage scar from a neovascular membrane with pigment migration at the macula.2 Fuch's spots, which form in 5.2% of pathologically myopic patients, are associated with poor acuity secondary to central scotomas due to the pigmented scar and surrounding atrophy.1,2,5
Clinicians must identify lacquer cracks early.10 ICGA can highlight the choroidal vasculature better than fluorescein angiography. ICG absorbs wavelengths of 790-805nm and fluoresces in the near-infrared range of 835nm. You need a scanning laser ophthalmoscope or infrared camera to visualize the fluoresced light, which lies outside the visual spectrum. Avoiding the visual spectrum allows the choroidal fluorescence to penetrate through opaque media such as blood, RPE and xanthophyll pigment.9,11 

On ICGA, choroidal neovascularization presents as a constantly hyperfluorescing area, often surrounded by a hypofluorescent rim.9 Once you identify and delineate the lacquer cracks and neovascular areas, you can follow them closely for progression. Investigators are exploring photocoagulation, surgical excision and interferon-alpha-2 as treatment options for neovascular membranes, but studies remain inconclusive.1 A high percentage of choroidal neovascular membranes resolve spontaneously, suggesting that observation is an option.3

The steady progression of pathological myopia brings with it a gradual loss of vision. Give patients fair warning upon diagnosis that the visual acuity they now appreciate may not always be. Warn them of the symptoms of retinal detachment and subretinal hemorrhage so that timely intervention may preserve the remaining vision. Thorough evaluation of these patients involves dilated fundus exams at least yearly.3 ICGA is recommended for its ability to visualize the entire choroidal circulation.9 In addition, axial length measurements can help determine the progression of the scleral ectasia.

Ms. Green is a fourth-year student at University of Houston College of Optometry. Dr. Kralich is an assistant professor there. The authors thank David Sherry, Ph.D., for producing the indocyanine green images.

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