2.2 Crystalline Retinopathy (Bietti) 55
Crystalline retinopathy is a condition first described by Bietti in 1937 [1]. Patients with crystalline retinopathy are initially seen when they are middle-aged because of reduced visual function. The alterations are often associated with night blindness and are slowly progres- sive. The fundus has numerous yellowish white glistening deposits resembling crystalline gran- ules scattered throughout the posterior pole in all retinal layers bilaterally [1]. Typically, the optic disks and retinal vessels are normal.
There may be marginal crystalline deposits in the cornea, and when present the deposits are sparkling yellow or white, round, polygonal, or needle-like crystals located in the anterior stroma in the perilimbal region [1, 2]. It has been reported that the crystalline deposits in the cornea can be detected more clearly by specular microscopy than by conventional slit- lamp examination [3]. Indeed, we have had cases in which the crystalline deposits were not detected by slit-lamp examination but were clearly seen by specular microscopy [4].
Photographs of the fundus and the cornea as seen by specular microscopy in two patients with crystalline retinopathy are shown in Fig. 2.14. Fluorescein angiography revealed diffuse atrophy of the RPE, and atrophy of the choriocapillaris is occasionally present in the areas corresponding to the depigmented areas.
The ophthalmoscopically observed crystalline deposits do not result in abnormal fluorescein findings. The progression of the disease process is similar in patients with and without crys- talline deposits in the cornea.
Changes in the fluorescein angiograms and visual field in a patient with Bietti’s crystalline retinopathy during a 5- to 6-year follow-up are shown in Fig. 2.15. Extensive areas of nonper- fusion of the choriocapillaries were present paracentrally that progressively enlarged and became confluent. The nonperfused areas extended to the periphery of the fundus during the 5- to 6-year follow-up. Visual field defects were detected in the areas corresponding to the nonperfused areas.
Full-field ERGs may be normal, reduced, or undetectable depending on the stage. The ERGs become progressively more depressed during the follow-up period as shown in Fig. 2.16. The amplitudes of the rod and cone components of the ERGs are reduced in parallel, indicating that both rods and cones are affected simultane- ously and almost equally.
The mode of inheritance is autosomal recessive, and it was recently found that this disease is caused by mutations in the CYP4V2 gene [5]. All of the patients whose ERGs were shown in this section had a mutation in this gene [6].
2.2 Crystalline Retinopathy (Bietti)
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56 2 Hereditary Retinal and Allied Diseases
Fig. 2.14. Crystalline deposits in the cornea (arrows) detected by specular microscopy (left) and in the poste- rior pole of the fundus (right) in two patients with Bietti crystalline retinopathy. (From Takikawa et al. [4])
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Fig. 2.15. Changes in fluorescein angiography (left) and the visual field (right) in a patient with crystalline retinopathy during a 5-year follow-up. (From Takikawa et al. [4])
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2.2 Crystalline Retinopathy (Bietti) 57
References
1. Bietti GB (1937) Uber familiares Vorkommen von
“Retinitis punctata albescens” (verbunden mit
“Dystrophia marginalis cristallinea corneae”), Glitzern des Glaskorpers und anderen degenera- tiven Augenveranderungen. Klin Monatsbl Augen- heilkd 99:737–756
2. Bagolini B, Ioli-Spada G (1968) Bietti’s tapetoreti- nal degeneration with marginal corneal dystrophy.
Am J Ophthalmol 65:53–60
3. Wakita M, Hayakawa M, Kato K, Kanai J (1990) Cases with crystalline retinopathy. Research Committee on Chorioretinal Degeneration, The
Ministry of Health and Welfare of Japan, Tokyo, pp 231–233
4. Takikawa C, Miyake Y, Yagasaki K (1992) Re- evaluation of crystalline retinopathy based on corneal findings. Folia Ophthalmol Jpn 43:969–978 5. Li A, Jiao X, Munier FL, Schorderet DF, Yao W, Iwata F, et al (2004) Bietti crystalline corneoretinal dys- trophy is caused by mutations in the novel gene CYP4V2. Am J Hum Genet 74:817–826
6. Lin J, Nishiguchi KM, Nakamura N, Dryja TP, Berson EL, Miyake Y (2005) Recessive mutations in the CYP4V2 gene in East Asian and Middle Eastern patients with Bietti crystalline corneoretinal dys- trophy. J Med Genet 42:e38
Fig. 2.16. Changes in full-field ERGs of the patient whose fundus is shown in Fig. 2.12. (From Takikawa et al. [4])
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