Optical Density Ratio of Intraretinal Fluid a Possible Prognostic Tool for VA in AMD

Eyes of wet AMD patients with higher optical density ratio values of intraretinal fluid from OCT were less likely to have a deterioration in BCVA over 36 months of follow up. This image from an older study shows a comparison of an ellipsoid form within subretinal fluid and a second form of the same dimensions within the vitreous.  Photo: Ahlers C, et al. Invest Ophthalmol Vis Sci 2009;50:3417-24. Click image to enlarge. These days, OCT is the principal diagnostic tool for age-related macular degeneration (AMD). It is widely available, noninvasive, fast and produces high-resolution digital images of the retina. A novel aspect of OCT images is the ability to calculate the optical density of distinct retinal cystic spaces (i.e., subretinal fluid, intraretinal fluid or pigment epithelial detachment) and the vitreous cavity; the ratio between these two can then be calculated. Previous optic density ratio calculations have clearly shown that not all subretinal fluid on OCT is the same and that subtle differences in pixel brightness of retinal fluids are associated with different pathologies.A team of researchers recently hypothesized that not all intraretinal fluid is the same and that different optical density ratios could have different prognostic significance on best-corrected visual acuity (BCVA) in eyes with wet AMD. They found that different ratio values were associated with different visual prognoses. Ratios of subretinal fluid and pigment epithelial detachment were not significantly associated with changes in BCVA.Inclusion criteria were treatment-naïve patients with wet AMD, BCVA of logMAR 2 (i.e., counting fingers) or better, treatment with at least three anti-VEGF injections, baseline macular OCT imaging and at least 36 months of follow-up. The treatment regimen in the researchers’ practice consisted of three initial monthly doses of bevacizumab (1.25mg/0.05mL) and then administration pro re nata.The team reviewed the records of 131 eyes from 116 patients diagnosed with treatment-naïve wet AMD who met the inclusion criteria. Of these, 86 eyes from 78 patients were eventually included in our analysis. The reasons for exclusion were other active ocular comorbidities in 27 eyes, missing or low-quality OCT imaging in 17 eyes and one eye with worse baseline BCVA than the inclusion criteria. Among the included cases, the average age of the patients was 77.8, 40% of patients were men and 48% were right eyes. Each patient received 8.7 anti-VEGF injections, and the mean logMAR BCVA values were 0.7 (about 20/100) at the initial visit and 0.6 (about 20/80) after 36 months.Eyes with higher optical density ratio values of intraretinal fluid were less likely to have a deterioration in BCVA over 36 months of follow-up. The researchers were led to believe that this ratio could be used as another OCT prognostic biomarker for BCVA in wet AMD patients.In wet AMD, the optical density ratio could represent the degree of vascular permeability resulting from the blood-retinal barrier breakdown. The resulting fluid exudation into the different retinal layers is expressed in different ratio values. The higher the permeability, the higher the ratio value.“In other words, not all intraretinal fluid images have the same properties, as can be seen by their different optical density ratio values,” the researchers wrote in their paper, which was published by Eye.The team did note that their retrospective study was based on a cohort from a single medical center, covering a relatively narrow geographic area and possibly curtailing the generalizability of the findings. Also, the patients in the study were primarily treated with bevacizumab according to the pro re nata protocol. This narrows their scope of inference concerning treatments with other anti-VEGF agents or using the treat-and-extend protocol. Nevertheless, the study concluded that some future studies should investigate the association of automated measurements of optical density ratio and the change in BCVA over time. Click here for the journal source.  Stanescu N, Khalifa K, Arnon R, et al. The association between optical density ratio of intraretinal fluid and visual acuity in neovascular age related macular degeneration after 36 months of follow-up. Eye (Lond). April 15, 2025. [Epub ahead of print].