Pamela Campos Figueroa_SCIENTIFIC POSTER 2015

Background:

Retinitis pigmentosa (RP) is an inherited disease characterized by photoreceptors and retinal pigment epithelium degeneration. The peripheral vision in patients with RP is highly compromised and the remaining central vision is associated with functional vision, and is commonly used to monitor disease development. As the disease progresses, patients undergo loss of visual acuity and color vision deficiency.

Purpose:

To determine whether results of color vision tests, Ishihara and Farnsworth-Munsell D-15 (FM D-15), could be good markers of RP central impairment. In that sense, the relationship among the foveal anatomical features, confirmed by Optical Coherence Tomography (OCT), and the visual parameters (visual acuity and different color vision indexes) in eyes with RP were analyzed.

Methods:

Thirty patients affected by retinitis pigmentosa (RP) were enrolled in the study. Cases with atypical or unilateral RP, epiretinal membrane, macular oedema, poor fixation because of extremely low visual acuity (< 0.01 in a decimal scale), myopic eyes with posterior staphyloma, and eyes with media opacities that affected visual acuity were excluded. The best corrected visual acuity (BCVA) was performed using standard Snellen eye charts and the number of errors by Ishihara and FM D-15 were quantified. Color Confusion Index (CCI), Selectivity Index (SI), and Confusion Index (CI), derived from FM D-15 test results, were also calculated. The external limiting membrane (ELM), the photoreceptor inner and outer segment junction (IS/OS), and the cone outer segment tips (COST) were assessed, using foveal OCT images, in three categories: distinct and continuous line (category 2), present but short line (category 1), and absent line (category 0). The presence/absence of the dome shape of the IS/OS layer, called foveal bulge (FB), were also analyzed. The central thickness of the macular area (CFT) and the peripapillary retinal nerve fiber layer (RNFL) were obtained automatically from OCT images. Structural-functional correlations were statistically analyzed using SPSS V19.

Results:

Twenty-five eyes of 25 patients, 6 (24%) males and 19 (76%) females, mean age 48 ± 15 (range 18-71) were included in the study. The average time from RP diagnosis to the study was 21 ± 14 years (range 3-49 years). Mean BCVA was 0.6 ± 0.3 (range 0.03-1 in decimal scale). Nineteen (76%) eyes had a BCVA more than 0.5 in a decimal scale. Twelve (48%) eyes showed no confusions on Ishihara test and 8 (32%) eyes disclosed 17 confusions (maximum level of confusion), been 7 confusions the average value. The results of FM D-15 displayed 6 cases (24%) with a perfect color vision (none confusion) and 2 (8%) with color blindness, been 7 confusions the average value. The angle or confusion axis was used to identify the type of color defect in the 19 eyes with color confusions by FM D-15. In this sense, 2 eyes (8%) showed blue-yellow color blindness (tritanope eyes), typical of early acquired color defects, 11 (44%) no specific axis of confusion (more than 80 °), typical of advanced acquired color defects, and 6 (24%) were misclassified (with more than 2 errors and the angle near normal values, between 60-70°). No protanope or deuteranope eyes were found in the sample. The most frequent ELM and IS/OS category was 2, in 15 eyes (60%) and 13 eyes (52%), respectively. COST most frequent result was category 0, in 16 eyes (64%). Thirteen eyes (52%) had lost the FB. Mean CFT in the sample was 223± 59 µm (range 131-352 µm). RNFL average was 102± 20 µm (range 67-168 µm). BCVA showed a medium to high significant positive correlation with ELM, IS/OS, COST and FB (rho range 0.733 to 0.869; p<0.01; Spearman´s rho test) and a significant but weaker positive correlation with CFT (rho= 0.420 p>0.05; Spearman´s rho test). No significant correlation was found between BCVA and RNFL. All the anatomical variables, except for CFT and RNFL displayed a medium to high significant negative correlation with the number of errors in both color vision tests (rho range -0.497 to -0.808; p<0.05 or p<0.01 as appropriate; Spearman´s rho test). Although relationships were similar, the number of errors in Ishihara test showed always strongest correlations with the anatomical features (rho range 0.509 to 0.808; p>0.05; Spearman´s rho test). Correlations between ELM, IS/OS, COST, and FB, and CCI and CI index were always significant but weaker than those obtained with the number of errors in the two color tests (rho range -0.427 to -0.561; p<0.05 or p<0.01 as appropriate; Spearman´s rho test). SI index only displayed weak negative significant correlations with COST (rho= -0.454; p<0.05; Spearman´s rho test).

Conclusions:

Although BCVA showed the strongest correlations with the anatomical features, a clear relationship was also found with color vision test results. It is plausible to think that color vision tests, especially FM D-15, may acquire more relevant role in other samples with earlier foveal alterations. Previous studies indicated that patients with RP and good BCVA could undergo color defects, mainly, tritanope. Among the studied color parameters, Ishihara test results were the best related to anatomical impairment, which could indicate that color deficiencies were not recent. This statement is supported by anatomical results since most of the eyes had lost COST, which represents the boundary of the cone outer segment tips and FB that, in healthy retina, is due to the higher number of membranous discs of most central cones. Therefore, color vision tests could be considered as good indicators of the progression of RP but their efficacy may change depending on the foveal impairment level.

Contact Details:

Email: pamelacamposfigueroa@gmail.com
Cell Phone: +34690839065