Time Domain versus Spectral Domain OCT in the Diagnosis and Treatment of Angioid Streaks

Time Domain versus Spectral Domain OCT in the Diagnosis and Treatment of Angioid Streaks
Andrea Lora, MD
Contributing Editor

Introduction
Since the introduction of OCT in 1991, it has become an invaluable tool in ophthalmic practice. OCT provides cross-sectional images of the retina using the reflectivity of light waves to obtain a profile of the retinal layers. The most widely used system is the Stratus® OCT 3 (Carl Zeiss Meditec, Inc.). This is based on time domain (TD) detection technology. The newest extension of OCT uses spectral domain (SD) technology. SD-OCT has improved image quality and acquisition. This allows for a larger set of actual data points allowing for accurate spatial correlations and mapping of individual retinal layers over a larger area in a shorter period of time. Cirrus® OCT (Carl Zeiss Meditec, Inc.) and Spectralis® HRA+OCT (Heidelberg Engineering, Inc) are based on this SD technology. The following demonstrates a case in which Cirrus SD-OCT imaged pathology that was not adequately captured using Stratus TD-OCT. This suggests that SD-OCT can provide additional morphological information compared with TD-OCT.

Case Report
A 40 year old female presented to the Emergency Room complaining of central vision distortion in her right eye for one week. She had poor vision in her left eye which had been stable for 3 years. Vision was 20/20 OD, 20/60 OS. IOP, pupils, EOM, and anterior segment exam was normal. Fundus exam revealed angioid streaks in both eyes with parafoveal subretinal hemorrhages OD, and a large amount of macular scarring and fibrosis OS (Figure 1). Dermatologic exam of her neck revealed small yellow papules with a “plucked chicken” appearance. Stratus OCT showed a small amount of subretinal fluid OD; and subretinal scarring and fibrosis OS (Figure 2). Cirrus SD-OCT illustrated breaks in Bruch's membrane (Figure 3) and subsequent choroidal neovascularization (CNV) (Figure 4) with subretinal fluid OD; and subretinal scarring, CNV, and intraretinal fluid OS (Figure 5). This patient was diagnosed with pseudoxanthoma elasticum with angioid streaks and CNV. She was treated with intravitreal Avastin in both eyes over the course of six months and had resolution of her symptoms and intraretinal fluid on OCT.


Figure 1 A. Fundus photo OD shows angioid streaks and parafoveal subretinal hemorrhage.


Figure 1 B. Fundus photo OS shows angioid streaks with macular scarring and fibrosis.


Figure 2 A. Stratus OCT OD reveals subretinal fluid.


Figure 2 B. Stratus OCT OS reveals scarring and fibrosis.


Figure 3 A. Cirrus OCT OD demonstrating a break in the RPE-Bruch’s complex.


Figure 3 B. Cirrus OCT OD close up view of the break.


Figure 3 C. Cirrus fundus reconstruction OD with markers delineating the angioid streaks.


Figure 4 A. Cirrus OCT OD showing CNVM formation.


Figure 4 B. Cirrus fundus reconstruction OD with markers through the CNVM.


Figure 4 C. Cirrus 3D retinal topographic reconstruction OD.


Figure 4 D. Cirrus 3D RPE topographic reconstruction OD.


Figure 5 A. Cirrus OCT OS demonstrating scarring, fibrosis, and intraretinal fluid.


Figure 5 B. Cirrus fundus reconstruction OS.


Figure 5 C. Cirrus 3D retinal topographic reconstruction OS

Discussion
Pseudoxanthoma elasticum is a multisystem connective tissue disorder with progressive calcification, fragmentation, and degeneration of elastic fibers, mainly affecting the skin, retina, and cardiovascular system. It is associated with a mutation in the ABCC6 gene. Ocular manifestations include angioid streaks, peau d’orange, optic nerve drusen, and choroidal neovascularization. Arvas et al. used TD-OCT to evaluate angioid streaks and described hyperreflective areas with masking effects that seemed to represent calcium deposits1; however breaks in the RPE-Bruch’s complex were not clearly seen. In this case, breaks in Bruch’s membrane and CNV were not adequately detected with Stratus TD-OCT and were better detected with SD-OCT. Occult CNV is an important finding in patients with angioid streaks, as early detection with SD-OCT and treatment may lead to improved patient education and visual outcome.

The failure to detect small breaks in the RPE-Bruch’s complex may be due to the following differences: TD-OCT has an axial resolution of about 10 microns; SD-OCT allows visualization of ocular structures to nearly 3 microns.2 Image acquisition differs from 400 A-scans per second with TD-OCT, to about 20,000-40,000 scans per second with SD-OCT.3 TD-OCT consists of only six radial scans and does not image the area between the scans. Therefore, TD-OCT captures only small representative sections of the macula and may miss important macular pathology. In contrast, SD-OCT scans include 3D topographic reconstructions and continuous scanning of the macula, containing over 65,000 scans in a 6 mm area, without excluding areas or need for interpolation.4 Therefore, small morphological changes can be detected with higher reliability with SD-OCT.

Conclusion
This case demonstrates certain advantages of SD-OCT over TD-OCT; including improved image acquisition, resolution, and more complete macular scanning. SD-OCT may contribute to a better understanding of the pathophysiology of retinal disease and in turn improve patient care.

References

  1. Arvas S. Akar S. Yolar M. Yetik H. Kizilkaya M. Ozkan S. OCT and angiography in patients with angioid streaks. Euro J of Ophthalmology. 12(6):473-81, 2002 Nov-Dec.
  2. Ko HT, Fujimoto JG, Schuman JS et al. Comparison of ultrahigh and standard resolution OCT for imaging macular pathology. Ophthalmology 2005; 112: 1922-1935
  3. Wojtkowski M, Srinivasan V, Fujimoto JG. Three-dimensional retinal imaging with high-speed ultra-high-resolution OCT. Ophthalmology. 2005; 112:1734-1746
  4. Srinivasan V, Wojtkowski M, Witkin AJ. High definition and 3D imaging of macular pathologies with high-speed ultrahigh-resolution OCT. Ophthalmology 2006:113:2054

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