Recent Optical Coherence Tomography Imaging of Vitreomacular Disorders
between displaced RPE and the outer part of Bruch’s membrane,53 is in agreement with histopathological studies.54
which Identification and
differentiation of such lesions from wet AMD is important, as treatment regimes differ, with PCV responding to photodynamic therapy.55,56
Epiretinal Membranes
ERMs are caused by glial proliferation on the surface of the macula and can cause varying degrees of vascular distortion, or even macular edema. OCT displays this membrane as a thin, smooth, hyper-reflective line along the surface of the retina (see Figure 4). Careful evaluation of the OCT can reveal the extent of ERM adherence to the underlying retina, the character of which correlates with the pathogenesis.57
Focal
attachments of the highly reflective ERM to the less reflective inner retinal surface can sometimes be easier to discern than global ERM adherence, which can make the ERM indistinct from the ILM. Focal adhesions are more commonly seen in secondary ERMs, while global adhesion is more prevalent in idiopathic ERMs.57
ERMs are usually
smooth, but can produce retinal folds, inner retinal irregularity and diffuse retinal thickening, which can be fully appreciated on 3D OCT rendering.58
3D scanning could also aid surgical planning as it reveals the manner and direction of ERM traction on the retina.58
Some studies have found a correlation between VA and retinal thickness in eyes with idiopathic ERMs;57 studies.59,60 evaluation60
however, this has not been found in other Higher-resolution OCTs have improved pre-operative ERM
Suh et al. also found that patients with intact IS/OS had better BCVA post-operatively. By grading the status of the IS/OS (see Figures 2 and 3) as present, absent or abnormal, Mitamura and colleagues found that logMAR BCVA correlated with both pre-operative CFT and IS/OS grades. However, at three and six months post-operatively, BCVA correlated only with the status of the IS/OS and not CFT. The percentage of eyes with a normal IS/OS gradually increased post-operatively.
Macular Holes
Full-thickness macular holes (FTMHs) are easily confused clinically with lamellar and pseudoholes. Accurate diagnosis is essential as management differs greatly. In one study, almost two-thirds of cases (63%) found to have a lamellar macular hole (LMH) on OCT were initially incorrectly diagnosed as either a FTMH, ERM or macular pseudohole on biomicroscopy.63 grading of FTMH status can guide the urgency of treatment.
OCT
LMHs are now primarily an OCT-based diagnosis as biomicroscopy provides insufficient resolution to detect residual outer retina, foveal
1. Huang D, Swanson EA, Lin CP, et al., Optical coherence tomography, Science, 1991;254(5035):1178–81.
2. Sacchet D, Moreau J, Georges P, Dubois A, Simultaneous dual-band ultra-high resolution full-field optical coherence tomography, Opt Express, 2008;16(24):19434–46.
3. Bourquin S, Seitz P, Salathe RP, Optical coherence topography based on a two-dimensional smart detector array, Opt Lett, 2001;26(8):512–4.
4. Yasuno Y, Miura M, Kawana K, et al., Visualization of sub-retinal pigment epithelium morphologies of exudative macular diseases by high-penetration optical coherence tomography, Invest Ophthalmol Vis Sci, 2009;50(1):405–13.
5. Srinivasan VJ, Adler DC, Chen Y, et al., Ultrahigh-speed optical coherence tomography for three-dimensional and en face imaging of the retina and optic nerve head, Invest Ophthalmol Vis
Sci, 2008;49(11):5103–10.
6. Rosen RB, Hathaway M, Rogers J, et al., Multidimensional en-face OCT imaging of the retina, Opt Express, 2009;17(5):4112–33.
7. Potsaid B, Gorczynska I, Srinivasan VJ, et al., Ultrahigh speed spectral / Fourier domain OCT ophthalmic imaging at 70,000 to 312,500 axial scans per second, Opt Express, 2008;16(19):15149–69.
8. Huber R, Adler DC, Srinivasan VJ, Fujimoto JG, Fourier domain mode locking at 1050 nm for ultra-high-speed optical coherence tomography of the human retina at 236,000 axial scans per second, Opt Lett, 2007;32(14):2049–51.
9. Wang RK, An L, Doppler optical micro-angiography for volumetric imaging of vascular perfusion in vivo, Opt Express, 2009;17(11):8926–40.
Summary and Future Directions
OCT has proved to be a powerful and versatile medical tool. It provides a non-contact method of objectively quantifying many conditions affecting the retina and has revolutionized the manner in which certain vitreomacular conditions are diagnosed and managed. It has shown promise as a tool for surgical planning and provides fine anatomical detail of the retina, which can aid post-operative prognostication. Newer-generation OCTs have already been widely used for research purposes and we eagerly await their commercial availability. n
10. Tao YK, Kennedy KM, Izatt JA, Velocity-resolved 3D retinal microvessel imaging using single-pass flow imaging spectral domain optical coherence tomography, Opt Express, 2009;17(5):4177–88.
11. Srinivasan VJ, Wojtkowski M, Witkin AJ, et al., High-definition and 3-dimensional imaging of macular pathologies with high- speed ultrahigh-resolution optical coherence tomography, Ophthalmology, 2006;113(11):2054, e1–14.
12. Wu Z, Vazeen M, Varma R, Chopra V, et al., Factors associated with variability in retinal nerve fiber layer thickness measurements obtained by optical coherence tomography, Ophthalmology, 2007;114(8):1505–12.
13. Wu Z, Huang J, Dustin L, Sadda SR, Signal strength is an important determinant of accuracy of nerve fiber layer thickness measurement by optical coherence tomography,
(see Figure 4) and have demonstrated that central foveal thickness (CFT) correlates with both pre-operative VA and IS/OS abnormalities.61,62
Gass also described the formation of LMH following chronic cystoid macular edema (CME).65
An observational case series reporting four
patients followed up with OCT confirmed that the occurrence of an LMH following refractory (diabetic) CMO is most likely due to the rupture of the inner wall of the thinned, cystic spaces. None of the four patients experienced any change in VA despite remarkable anatomical reduction in foveal thickness (from a mean of 509 to 166µm). In all cases, high-resolution OCT revealed that the outer retinal layer remained, with at least intermittently recognisable IS/OS.69
FTMHs have been extensively investigated with the use of OCT; the clinical features associated with improved visual prognosis are well-known and include better VA on presentation, duration of symptoms and hole diameter.70–72
Post-operatively, a few studies have
revealed that the presence of an intact IS/OS is an important indicator of visual recovery, with the number of patients with detectable IS/OS increasing over time following FTMH repair.37
of the IS/OS line on OCT correlates well with VA,36–38
The post-operative status with a significant
correlation between the post-operative presence of the IS/OS and the pre-operative duration of symptoms.
Post-operative IS/OS line ‘healing’ appears to occur at differing rates,36,37 and it is still unknown how some patients continually show gradual visual recovery years after FTMH repair. There are probably numerous other prognostic determinants yet to be discovered as, histologically, photoreceptors are reported to remain intact in the fluid cuff of a FTMH73
segments.74
These findings infer photoreceptor recovery and provide signs of anatomical success on an almost histological scale.
photoreceptors, or intraretinal split,63 the presence of which explains the
relatively preserved vision in this group of patients. The almost constant finding of an ERM in the presence of LMH63,64 evolution. Gass,65
along with a few other authors,66–68 were a result of an abortive process of a FTMH.
could shed light on its proposed that LMHs
and, if viable, could possibly regenerate inner and outer
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