OSNE 300 Survey

I can not think of doing cataract surgery today without the use of an OCT to diagnose vitreo-macular traction, epi-retinal membranes, etc. that were previously undiagnosed. It simply makes predicting the expected outcome so much more scientific and accurate. I find it very useful, too, in terms of following glaucoma and the health of the optic nerve in general. It also has a corneal function that helps with determining LASIK flap thickness from prior procedures. In summary, OCT is an indispensable tool in the modern ophthalmic practice in my opinion.

In recent years OCT became more and more important in daily practice. With the improvement in resolution, OCT is mandatory in daily practice. A general practioner, as well as a cataract or refractive surgeon, benefits greatly from these diagnostic tools. High quality images from the cornea can identify the depth of opacities and the density and the impact on the visual quality of our patients. Anterior segment imaging is very useful for the surgeon taking into account the lens rise, the configuration of the iris and the dimensions of the angle before performing surgery. And last but not least retinal OCT gives information about posterior vitreous detachment, possible cystoid macular edema, macular puckers, etc. With these high tech OCT instruments we can make more accurate diagnosis and help our patients enjoy their vision.

When anti-VEGF therapy became the routine approach to patients with wet-AMD, most physicians started using time domain OCT for guiding re-treatment. As a result, visual acuity loss was combined with morphologic changes — ie, a 100 µm increase in central retinal thickness — in the majority of re-treatment algorithms. Although this approach rarely led to the maintenance of the initial visual gain after the initial dosing with three anti-VEGF injections, most of us believed that OCT evaluation was the way to go.

The right answer to our needs came along very soon when spectral domain OCTs were introduced into the market. Faster scans with higher resolution revealed newer features which could not be appreciated with the old “primitive” time domain technology. A fuzzy puzzle of colored pixels was replaced by a well defined, high resolution scan which provided precious previously unknown features.

Still, there are some issues in spectral domain macular thickness segmentation as this procedure is frequently associated with errors in the measurement. Moreover, the decrease in the manual central retinal thickness may or may not correlate with the improved visual acuity depending on the machine used. As a result, a true morphologic qualitative evaluation instead of a quantitative thickness measurement is now used to decide whether the patient needs a retreatment or not.

In addition to the precise identification of the presence of intra- and sub-retinal fluid, current machines allow newer findings which can be used to guide anti-VEGF therapy and as prognostic factors. A series of tomography features such as the ellipsoid zone, the external limiting membrane (ELM), hyper-reflective dots into the retinal layers, subretinal thickening, outer retinal tubulations, outer segment stalactites and many others can be detected, assessed and monitored with modern OCTs.

Other conditions other than AMD can be better characterized with spectral domain technology. A hyper-reflective lesion with fuzzy borders and absent or altered IS/OS junctions is more meaningful than central retinal thickness in the evaluation of myopic CNV activity.

As said, much interest is now focused on the possibility to identify prognostic factors which may aid in optimizing treatment outcomes. In eyes with DME, mean disrupted IS/OS and ELM length have the greatest correlation coefficient with final VA. This is also true in macular edema secondary to branch vein occlusion. In patients with wet AMD, the presence of intraretinal fluid has a negative correlation with final VA and recurrent subretinal fluid rather than intraretinal fluid is a sign of reactivation of the disease. In contrast, there is no correlation between VA and behavior of sub pigment epithelium detachment fluid.

In conclusion, the use of OCT technology has allowed significant improvements in the management of patients with wet AMD and other retinal conditions. Retinal thickness (ie, 100 µm) per se as a guide for anti-VEGFs treatment is no longer valid and has provided sub-optimal outcomes in the past, especially in the era of time domain OCTs. With the advent of SD-OCTs, specific morphological patterns (ie, subretinal fluid) can guide treatments more accurately. Moreover, SD-OCT can identify potential prognostic factors (ellipsoid zone, ELM, IS/OS junction, IRF, SRF, tubulation) to further characterize patients and efficiently individualize therapy.

Today, wet AMD cannot be managed without the aid of OCT.