Correlation of Inner Segment Outer Segment Photoreceptor Status to Retinal Point Sensitivity in Diabetic Macular Edema

Abstract

 

Purpose:

 

To evaluate the relationship between retinal point sensitivity and inner segment/outer segment photoreceptor (IS/OS) status measured using a combined microperimetry (MP) - optical coherence tomography (OCT) system in patients with diabetic macular edema (DME).

 

Methods:

 

We performed a cross sectional study of patients managed at a university based retinal practice. Demographic data including, age, gender, and race was collected. Simultaneous fundus MP and OCT was obtained for each of the patients using OPKO/OTI automated system (Toronto, Canada). Retinal sensitivity and thickness at each MP point was recorded. A point-by-point analysis of presence or absence of the IS/OS layer at every MP point was performed by a trained reviewer. OCT scans were reviewed to determine the type of DME; cystoids macular edema (CME) or diffuse (absence of any cysts). Fixation stability and fixation location were recorded.Exploratory data plotting and statistical summaries were performed for the study and confounding variable. Confounding variables considered for the analysis between point sensitivity and IS/OS status included type of DME, fixation stability, fixation location, age, gender and race. A mixed linear model with random intercepts was constructed to evaluate the relationship between IS/OS status and point sensitivity and adjust for confounding variables.

 

Results:

 

We analyzed records and images of 25 patients (37 eyes). Mean age of our patients was 64.16 years. 19 patients were male (29 eyes) and 6 were female (8 eyes). 25 eyes (68%) had stable fixation and 12 eyes (32%) had relatively unstable fixation. 30 eyes (81%) had centric fixation while 3 (8%) had paracentric and 4 (11%) and eccentric fixation. 27 eyes had CME and 10 eyes had diffuse DME. Mean central subfield thickness was 325 µm.A total of 1036 individual MP points were analyzed. Mean point sensitivity was 10.51 dB. 793 points (76.5%) had IS/OS layer present and 243 points (23.5%) had IS/OS layer disrupted. Using our mixed linear model to adjust for potential confounders, we found that the absence of the IS/OS junction was significantly associated with a 5.33 dB decrease in retinal point sensitivity (p=0.0008).

 

Conclusions:

 

In this index study, we have demonstrated that disruption of the IS/OS junction is correlated with a significant decrease in point sensitivity measured by MP in eyes with DME. Further studies are indicated to confirm such relationship and to establish causality.

 

Keywords: diabetic retinopathy • retina: distal (photoreceptors, horizontal cells, bipolar cells) • perimetry