L’edema maculare diabetico rappresenta una delle maggiori cause di riduzione dell’acuità visiva nei Paesi industrializzati.
Negli anni passati numerosi trial clinici hanno cercato di valutare il migliore trattamento possibile per l’edema basandosi sui dati relativi allo spessore maculare ottenuto mediante l’impiego dell’OCT.
Tuttavia la correlazione tra spessore retinico maculare misurato all’OCT e l’acuità visiva è stato dimostrato essere scarsa e variabile in molti casi.
L’utilità clinica della misurazione dello spessore maculare appare quindi controversa e sicuramente non può essere considerata predittiva dell’acuità visiva.
Scopo dello studio è valutare e quantificare la lunghezza del segmento esterno dei fotorecettori in un gruppo di 27 pazienti affetti da edema maculare diabetico mediante l’impiego dello SD-OCT e determinare la correlazione tra variazione della misurazione e acuità visiva.
I risultati evidenziano come ci sia una forte correlazione nei pazienti affetti da edema maculare diabetico e alterazione della lunghezza dei fotorecettori, dimostrando come una significativa percentuale di variazione dell’acuità visiva possa essere spiegata con la variazione/alterazione della lunghezza dei fotorecettori.


Retina the journal of retinal and vitreous diseases
Relationship between Photoreceptor Outer Segment Length and Visual Acuity in Diabetic Macular Edema

Forooghian F, Stetson PF, Meyer SA, Chew EY et al.

Retina
2010;30:63-70


Purpose: The purpose of this study was to quantify photoreceptor outer segment (PROS) length in 27 consecutive patients (30 eyes) with diabetic macular edema using spectral domain optical coherence tomography and to describe the correlation between PROS length and visual acuity.

Methods: Three spectral domain–optical coherence tomography scans were performed on all eyes during each session using Cirrus HD-OCT. A prototype algorithm was developed for quantitative assessment of PROS length. Retinal thicknesses and PROS lengths were calculated for 3 parameters: macular grid (6 × 6 mm), central subfield (1 mm), and center foveal point (0.33 mm). Intrasession repeatability was assessed using coefficient of variation and intraclass correlation coefficient. The association between retinal thickness and PROS length with visual acuity was assessed using linear regression and Pearson correlation analyses. The main outcome measures include intrasession repeatability of macular parameters and correlation of these parameters with visual acuity.

Results: Mean retinal thickness and PROS length were 298 μm to 381 μm and 30 μm to 32 μm, respectively, for macular parameters assessed in this study. Coefficient of variation values were 0.75% to 4.13% for retinal thickness and 1.97% to 14.01% for PROS length. Intraclass correlation coefficient values were 0.96 to 0.99 and 0.73 to 0.98 for retinal thickness and PROS length, respectively. Slopes from linear regression analyses assessing the association of retinal thickness and visual acuity were not significantly different from 0 (P > 0.20), whereas the slopes of PROS length and visual acuity were significantly different from 0 (P < 0.0005). Correlation coefficients for macular thickness and visual acuity ranged from 0.13 to 0.22, whereas coefficients for PROS length and visual acuity ranged from −0.61 to −0.81.

Conclusion: Photoreceptor outer segment length can be quantitatively assessed using Cirrus HD-OCT. Although the intrasession repeatability of PROS measurements was less than that of macular thickness measurements, the stronger correlation of PROS length with visual acuity suggests that the PROS measures may be more directly related to visual function. Photoreceptor outer segment length may be a useful physiologic outcome measure, both clinically and as a direct assessment of treatment effects.