Objective analyses of tessellated fundi and significant correlation between degree of tessellation and choroidal thickness in healthy eyes

Abstract

A tessellated fundus is a common characteristic of myopic eyes and is an important clinical marker for the development of retinochoroidal changes. However, the exact cause and significance of tessellated fundi have not been definitively determined. We determined the degree of tessellation in fundi objectively in normal, non-pathological myopic eyes, and correlated the degree of tessellation and the choroidal thickness (CT) and axial length (AL). This was a prospective observational cross sectional study. The eyes were classified subjectively into three groups based on the degree of tessellation observed ophthalmoscopically. Digital color fundus photographs were assessed for the degree of tessellation by ImageJ, an image processing program. Three tessellated fundus indices (TFIs) were calculated and were compared to the three subjectively-determined groups. The subfoveal and nasal CTs were measured in the optical coherence tomographic images. The correlations between the TFIs and the CT were calculated. Additionally, the correlation between the TFIs and the AL was calculated. One hundred right eyes of 100 healthy volunteers (mean age 25.8±3.9 years) were studied. Ophthalmoscopically, 57 eyes were placed in the non-tessellated group, 27 eyes into the weakly tessellated group, and 16 eyes into the strongly tessellated group. There was a significant correlation between the subjective classifications and the TFI values (P<0.05, Kruskal-Wallis test). All of the TFIs were significantly associated with the subfoveal and nasal CT (R = -0.20 to -0.24, P<0.05). The TFIs were not significantly correlated with the ALs. In conclusion, the significant correlation between the subjective and objective classifications of the degree of tessellation indicates that TFIs can be used to classify the degree of tessellation. The results indicate that the differences in the CT account for the degree of tessellation.

Figure 1. Quantitative analysis of digital color fundus photographs.

An area between the fovea and the optic disc was selected as shown by the yellow circle (left). The same color fundus photograph showing the red, green and blue pixels using image J (right). In the histograms, the horizontal bar indicates the brightness of each color. Note that the vertical scale is different for the different histograms. Below each histogram, the mean, standard deviation, minimum, maximum, median, and count for each color are shown.

Figure 2. Box plot of subjective classification of tesselation and the TFI values of TFI-1, TFI-2 and TFI-3.

For each TFI, the eyes in the strongly tessellated group (ST) had a significantly higher TFI values than those in the non-tessellated group (NT). Those in weakly tessellated group (WT) were in between. The only exception was NT and WT in TFI 2 (Steel-Dwass test. *P<0.05; **P<0.01; n.s., not significant).

Figure 3. Scatter diagrams of TFIs and subfoveal choroidal thickness (SFCT) and nasal choroidal thickness (NCT).

There was a significant and negative correlation between each of the TFIs and both the subfoveal and nasal CTs except for that between TFI-1 and the nasal CT. TFI; tessellated fundus index.

Figure 4. Scatter diagrams of TFI and axial length.

No significant correlation was observed between any of the TFIs and axial length. TFI; tessellated fundus index.

Figure 5. Scatter diagrams of choroidal thickness (CT) and axial length.

There was a significant and negative correlation between axial length and both the subfoveal CT and nasal CT.