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Fine retinal crystalline deposits observed by confocal scanning laser ophthalmoscopic examination using infrared light
  1. Y Yanagi,
  2. Y Tamaki,
  3. H Fukushima
  1. Department of Ophthalmology, University of Tokyo School of Medicine, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
  1. Correspondence to: Yasuo Yanagi, Department of Ophthalmology, University of Tokyo School of Medicine, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan; yanagi-tky{at}umin.ac.jp

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Bietti's crystalline retinopathy is a tapetoretinal degeneration characterised by numerous tiny sparkling yellow-white spots mainly located in the deeper layer of the posterior pole retina.1 Since crystalline deposits tend to become small and decrease in number over time,2,3 the fundus appearance becomes indistinguishable from other retinal dystrophies with time.4 The advent of confocal scanning laser ophthalmoscope (SLO) with infrared light has enabled high sensitive examination of the deep layer of the retina.5 We studied the deep retinal abnormalities in a case with a typical Bietti's crystalline retinopathy and in another case with myopic chorioretinal atrophy throughout the posterior pole. Consequently, we detected numerous fine crystalline deposits in both cases, which were not detected with other funduscopic examinations.

Case reports

Case 1

A 52 year old man was referred to our hospital by his ophthalmologist who found an abnormal fundus appearance. There was no consanguinity. Best corrected visual acuity was 20/24 right eye and 20/50 left eye. No abnormalities were found in the anterior segment and media. Fine crystalline deposits were not detected in the corneal stroma of either eye. Funduscopic examination revealed numerous fine reflective crystalline deposits throughout the posterior pole and mid-peripheral retina of both eyes. Most of these deposits were in the deep retina and subretina but some deposits were superficial. Goldmann perimetry showed relative scotomas in a zone within 30–40 degrees of the central field in both eyes. Fluorescein angiography of both eyes showed island-like hypofluorescence lesions surrounded by hyperfluorescent lesions in the early phase. Indocyanine green angiography also showed the atrophy of the choriocapillaris in the posterior pole. Crystalline deposits did not show any fluorescence in either fluorescein or indocyanine green angiography.

The retinal crystalline deposits were more clearly visible with the fundus examination by SLO (Rodenstock, Germany) using infrared light compared to the routine funduscopic examinations (Fig 1). Each crystal deposit appeared larger in size. In addition, numerous fine crystal deposits were evident, which were not observed by conventional funduscopic examinations including ophthalmoscopy and slit lamp biomicroscopy using a contact lens. When the source of light was moved, the crystalline deposits scattered light and became more prominent.

Figure 1

Ocular fundus of case 1. Fundus photograph (A), grey scale image of the same fundus photograph (B) and SLO image with infrared light (C) are shown. Note that the crystalline deposits are most evident with the infrared imaging.

Case 2

A 52 year old woman visited our hospital complaining of gradual visual loss in both eyes. She also noticed night blindness since childhood. Her parents were both high myopic and consanguineous. The extracapsular cataract extraction surgery was performed without complications in both eyes at the age of 43, and referring ophthalmologist reported that her fundus showed extensive chorioretinal atrophy in both eyes and that best corrected visual acuity was 20/1000 right eye and 20/1000 left eye after the cataract surgery. At initial visit to our hospital, best corrected visual acuity was right eye 20/200 and left eye 20/1000. Conjunctiva, cornea, anterior chamber, and vitreous were normal in both eyes and no fine crystal deposits were found at limbs of either cornea. Both eyes were aphakic and the posterior lens capsules were intact but relatively opaque. Funduscopic examination revealed the posterior staphyloma and the extensive atrophy of the retinal pigment epithelium and choriocapillaris extending from the posterior to mid-peripheral retina in both eyes. Optic disc showed myopic appearance. Retinal vessels and peripheral retina showed normal appearance. Standard electroretinogram was non-recordable. Goldmann perimetry showed marked constriction of all isoptres and loss of visibility of I-4-e isoptre for both eyes. During a 5 year follow up, visual acuity and the fundus appearance were stationary. Fluorescein angiography performed at the age of 57 demonstrated hypofluorescence throughout the posterior pole in the early phase and diffuse hyperfluorescence in the later phase. Indocyanine green angiography disclosed the loss of background veil-like fluorescence throughout the posterior pole due to the choriocapillaris atrophy.

Fundus examination by the confocal SLO with infrared light disclosed numerous tiny crystalline deposits in the posterior pole (Fig 2), which were not evident with other funduscopic examinations, including ophthalmoscopy and biomicroscopy with a contact lens, or with fluorescein or indocyanine green angiographic studies. The deposits scattered light when the source of light was moved to cause them sparkle, similar to the fine crystalline deposits observed in the fundi of case 1.

Figure 2

Ocular fundus of case 2. Fundus photograph (A), grey scale image of the same fundus photograph (B) and SLO image with infrared light (C). Magnified image of the boxed area is shown in (D). Note that numerous crystalline deposits are observed with the SLO imaging.

Amino acid analysis and other examinations did not show any abnormal value.

Comment

The diagnosis of Bietti's crystalline retinopathy in case 1 is based on the retinal crystalline and supported by the characteristic island-like hypofluorescence observed by fluorescein angiography.2 Fundus examination by SLO with the infrared light disclosed numerous tiny crystalline deposits, which were not observed by conventional fundus examinations. Thus, in Bietti's crystalline retinopathy, there are more numerous accumulation of retinal crystalline deposits than can be observed by funduscopic examinations.

In case 2, numerous tiny retinal crystalline deposits were detected by SLO with infrared light, although no other examinations disclosed these crystalline deposits. We have not observed such retinal crystalline deposits in other cases with myopic chorioretinal atrophy, suggesting the accumulation of crystalline deposits is not a generalised feature of myopic chorioretinal degeneration. Crystalline deposits, prerequisite for the diagnosis of Bietti's crystalline retinopathy, are difficult to detect in advanced cases.2–4 Since crystalline deposits do not block or transmit fluorescence in fluorescein2 or indocyanine green angiography, diagnosis of Bietti's crystalline retinopathy in advanced cases without funduscopically apparent crystalline deposits have been established only when family history was contributory.4 Because the presence of crystalline material in the peripheral lymphocyte4 was not observed by transmission electron microscopy, whether case 2 can be categorised as Bietti's crystalline retinopathy or a distinct clinical entity awaits further investigation. Additionally, to our knowledge, Bietti's crystalline retinopathy with degenerative myopia has not been reported in the literature. However, the presence of parental consanguinity of this case might suggest an autosomal recessive inheritance, similar with some reported cases with Bietti's crystalline retinopathy, and the striking resemblance of the morphology of the tiny crystalline deposits observed by SLO using infrared light between the two cases may support that underlying pathogenesis is similar.

References

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