Examination of patients with cystoid macular edema using a scanning laser ophthalmoscope with infrared light

Scanning laser ophthalmoscopy retroillumination: applications and illusions

Scanning laser ophthalmoscopes (SLOs) are used widely for reflectance, fluorescence or autofluorescence photography and less commonly for retroillumination imaging. SLOs scan a visible light or near-infrared radiation laser beam across the retina, collecting light from each retinal spot as it’s illuminated. An SLO’s clinical applications, image contrast and axial resolution are largely determined by an aperture overlying its photodetector. High contrast, reflectance images are produced using small diameter, centered apertures (confocal apertures) that collect retroreflections and reject side-scattered veiling light returned from the fundus. Retroillumination images are acquired with annular on-axis or laterally-displaced off-axis apertures that capture scattered light and reject the retroreflected light used for reflectance imaging. SLO axial resolution is roughly 300 μm, comparable to macular thickness, so SLOs cannot provide the depth-resolved chorioretinal information obtainable with optical coherence tomography’s (OCT’s) 3 μm axial resolution. Retroillumination highlights and shades the boundaries of chorioretinal tissues and abnormalities, facilitating detection of small drusen, subretinal drusenoid deposits and subthreshold laser lesions. It also facilitates screening for large-area chorioretinal irregularities not readily identified with other en face retinal imaging modalities. Shaded boundaries create the perception of lesion elevation or depression, a characteristic of retroillumination but not reflectance SLO images. These illusions are not reliable representations of three-dimensional chorioretinal anatomy and they differ from objective OCT en face topography. SLO retroillumination has been a useful but not indispensable retinal imaging modality for over 30 years. Continuing investigation is needed to determine its most appropriate clinical roles in multimodal retinal imaging.

Quantitative analysis of cystoid macular edema using scanning laser ophthalmoscope in modified dark-field imaging

PURPOSE

To quantitatively analyze cystoid macular edema (CME) using scanning laser ophthalmoscope in the modified dark-field imaging.

METHODS

We studied 37 eyes with CME associated with different diseases before and after treatment. The CME area was measured with the modified dark-field imaging and fluorescein angiography. The best-corrected visual acuity, mean deviation and macular sensitivity measured by Humphrey automated perimetry, and foveal thickness and macular volume determined by optical coherence tomography were investigated.

RESULTS

The CME area could be clearly outlined in 50% with the fluorescein angiography and in 100% with the modified dark-field imaging (P < 0.0001). The CME area calculated using the modified dark-field imaging was significantly correlated with that using the fluorescein angiography (P = 0.0001). Before treatment, the CME area calculated using the modified dark-field imaging was significantly correlated with only the macular volume (P = 0.0230). Three months after treatment, decrease in the CME area was significantly correlated with improvement in the best-corrected visual acuity, mean deviation, macular sensitivity, foveal thickness, and macular volume (P < 0.05 for all).

CONCLUSION

Our findings indicate that scanning laser ophthalmoscope in the modified dark-field imaging can measure the CME area and is useful in analyzing CME quantitatively. The findings can also be used to evaluate the effectiveness of treatment.

Scanning laser ophthalmoscopy in the retromode in diabetic macular oedema

PURPOSE

To determine the validity of scanning laser ophthalmoscopy in the retromode (RM-SLO) versus other imaging modalities in the diagnosis of diabetic macular oedema (DME).

METHODS

Two hundred and sixty-three eyes were examined. Inclusion criteria were any stage of untreated or treated diabetic retinopathy and four imaging modalities of the macula carried out on the same day: time domain optical coherence tomography (OCT), fundus autofluorescence (FAF), RM-SLO and fluorescein angiography (FA). Two masked retinal specialists independently graded all images. Agreement between RM-SLO and OCT, FA and FAF in evaluating the presence and patterns of DME was evaluated by kappa statistics, sensitivity, specificity, observed proportional agreement, and proportional agreement in positive and negative cases.

RESULTS

The agreement in evaluating the presence/absence of DME between RM-SLO and OCT, FA and FAF was good: κ = 0.73 (confidence interval; CI, 0.64-0.83), κ = 0.71 (CI, 0.61-0.81) and κ = 0.73 (CI, 0.63-0.83), respectively. The agreement in evaluating cystoid pattern of DME was almost perfect between RM-SLO and OCT, RM-SLO and FA, κ > 0.8; and good between RM-SLO and FAF, κ > 0.7. The agreement in evaluating the presence/absence of subfoveal neuroretinal was almost perfect between RM-SLO and OCT (κ = 0.83; 95% CI, 0.70-0.96). Subfoveal neuroretinal detachment did not show any specific pattern on FA or FAF. Sensitivity and specificity of RM-SLO in evaluating DME was 97.7% and 71.9% versus OCT, 97.4% and 68.1% versus FA and 96.1% and 73.3% versus FAF. Retinal thickness of 233 μm represented the cut-off value to define DME by RM-SLO.

CONCLUSIONS

The combined use of non-invasive imaging techniques can improve the diagnostic interpretation of different aspects of DME.

[Infrared imaging of outer lamellar macular holes]

BACKGROUND

Outer lamellar macular holes (OLMH) are very rare compared to inner lamellar macular holes. An OLMH can occur associated with optic pit maculopathy, in the progression of myopic macular retinoschisis, transient in the development of full thickness macular holes or idiopathic. This article reports on infrared imaging of OLMHs.

METHODS

Infrared (IR) images in 2 patients aged 22 and 34 years with OLMH were taken using IR reflection at a wavelength of 820 nm with a confocal scanning laser ophthalmoscope (Heidelberg Retina Angiograph 2, Heidelberg Engineering). IR images were correlated with linear optical coherence tomography (OCT) scans (Stratus-OCT, Zeiss). Images were acquired during follow-up of up to 30 months and if applicable preoperatively and postoperatively.

RESULTS

Clear infrared signals were recorded especially in OLMH associated with optic pit maculopathy. Correlation with linear OCT scans showed the enhanced infrared signals to be restricted to the extent of the OLMH. The borders of the OLMH could be clearly delineated. Infrared imaging enables a top view of OLMH and therefore allows an excellent documentation of the course of OLMH.

CONCLUSIONS

Infrared reflection is useful for two-dimensional imaging of OLMH. Infrared imaging can provide a supplement to slice imaging for OCT diagnostics and allows monitoring of OLMH over time. The postoperative sequence of OLMH closure in patients with optic pit maculopathy can be studied in more detail using infrared imaging.

Visualization of cystoid macular oedema using a scanning laser ophthalmoscope in the retro-mode

PURPOSE

To investigate cystoid macular oedema using a scanning laser ophthalmoscope.

METHODS

We retrospectively reviewed the medical records of 101 eyes with cystoid macular oedema because of various aetiologies. All eyes were examined with a new, commercially available scanning laser ophthalmoscope in the retro-mode with an infrared laser.

RESULTS

In all eyes, scanning laser ophthalmoscope in the retro-mode showed numerous oval or polygonal cystoid spaces. Most eyes showed a large cystoid space beneath the fovea, with surrounding small cystoid spaces. The area of the foveal cystoid space showed a correlation with its height, as measured with optical coherence tomography (R = 0.60, P < 0.0001). Visual acuity, however, did not show any correlation with either the area of the foveal cystoid space or area of all of the cystoid spaces in the macular area.

CONCLUSION

Scanning laser ophthalmoscope in the retro-mode can show each cystoid space located in any layer of the retina and allows us to detect the extent of cystoid macular oedema.