Study of the Correlation Between Macular Thickness Analyzed by Optical Coherence Tomography and the Visual Functions in Retinitis Pigmemtosa

The diagnosis of RP was according to the typical clinical history of night blindness, characteristically findings of "bone-spicule" change in the fundus, and varying degrees of peripheral visual field constriction. According to the affected loci in the fundus, we defined a typical type of RP as the retinal pathological change was around the banded area outside the main vascular arcs, and a central variant of RP stood for those with bone-spicule change appeared at the macula.[17] The exclusion criteria included eyes with histories of trauma, intraocular laser treatment, intraocular surgery, presence of retinal diseases, high degree of myopia with refraction more minus than -8.0 D or hyperopia with refraction more than +5.0 D. Patients with systemic diseases that may affect retina like diabetes or hypertension were also excluded.

Visual acuity was examined with a Snellen visual chart with a calibrated luminance. Then according to the equation that Snellen VA equals to 1/MAR (MAR= minimal angle of resolution), Snellen VA was converted into logMAR for statistics. For calculation, visual acuity of hand motion was converted into 20/2000 and light perception was converted into 20/20000 of Snellen fraction. Visula field examination was evaluated using Goldmann kinetic perimetry with varying sizes and illuminations of testing light spots. Then the degree of the widest visual field isopter was recorded. EOG: is used to assess function of retinal pigment epithelium. During dark adaptation, resting potential decreases slightly and reaches a minimum ("dark trough"). When the light is on, the resting potential increases ("light peak"). The ratio of light peak voltage versus dark trough voltage is known as the Arden ratio. The EOG was performed with pupil dilated, first in the dark for 15 minutes, and then in the light for 15 minutes and the Arden ratio for analysis was recorded.

Color sense discrimination test was evaluated using Farnsworth Munsell 100-Hue test (Munsell FM 100, X-Rite, USA). Each patient arranged four trays of colored caps in hue order. There is a predetermined sequence for each tray. The closer the patient's arrangement is to the correct sequence, the better the patient's color sense discrimination. The Farnsworth-Munsell 100-Hue Test Scoring Software was used to score the results of Farnsworth-Munsell 100-Hue Test. The results are displayed in polar or linear format, and the total error score was recorded for calculation.

OCT was performed with the ultimate commercial OCT units (OCT3, Carl Zeiss Meditec, Inc, Dublin, CA) to measure the macular thickness under papillary dilatation by an experienced examiner. The retinal thickness was calculated using OCT retinal mapping software (version 6.1 a), which measured thickness of nine divided macular regions after six scans with 6 mm long centered on the patient's fixation point by means of an inner fixation target (Figure 1), and expressed as a color-coded map. Internal fixation was essentially chosen due to better reproducibility. We defined the foveal area as the area centered at fixation with a diameter of one millimeter, the inner ring as the area between circles with diameter of one and three millimeters, and outer ring as the area between circles with diameter of three and six millimeters (Figure 2).

We analyzed and compared the patients' characteristics, results of visual function tests and macular tomography in these two groups of RP. Then we tried to find out if there were correlations between macular tomography and visual function tests