¡¡¡¡Table 2  Sensitivity, MD, PSD and RNFL thickness at different sectors£¨ÂÔ£©

¡¡¡¡A: POAG with highly myopia;B: POAG with nonª²highly myopia;C: Highly myopia without POAG;D: Normal control
           
¡¡¡¡Table 3  The association between mean sensitivity and RNFL thickness with logistic regression£¨ÂÔ£©

¡¡¡¡Methods  Optisal coherent tomography OCT (OCTª²2000, Zeiss) was used to measure the thickness of the peripapillary RNFL. Measurements were made at 100 points along a circle concentric with the optic nerve head at a radius of 1.73mm. These were used to calculate the average RNFL thickness for each of 45 sectors.

¡¡¡¡Visual field examination optisal coherent tomography  All subjects underwent achromatic automated static perimetry with the swedish interactive threshold algorithm (SITA) standard of the Humphrey Field Analyzer 750 (Allergan Humphrey, San Leandro, CA). A reliable test was defined as having fewer than 20% falseª²positive or falseª²negative scores and fewer than 33% fixation losses. Then we divided the result of visual field to four sectors according to the average RNFL thickness measured by OCT. we calculated the average sensitivity in each sector. And then we adjusted the result for the chiasma of nerve fiber.

¡¡¡¡Statistical Analysis  Chiª²square test was used to analyse the results of visual field, and oneª²way analysis of variance to evaluate the RNFL thickness. The correlation between mean sensitivity and RNFL thickness in the same sector was evaluated by Pearson¬ðs correlation coefficients. The software package SPSS 12.0 was used for statistical analysis.

¡¡¡¡RESULTS

¡¡¡¡The POAG with highly myopia group was registered as the loss of total sensitivity at the total deviation probability plot, however in the pattern deviation probability plot it was registered as special visual field losses which were found in early POAG. There were significant differences among the four group(¦Ö2=32.293£¬P=0.000, Table 1), by partition of chiª²square the differences among the POAG with highly myopia group and others was significant£¨P£¼0.01), the same difference was found between POAG with nonª²highly myopia group and highly myopia without POAG group (P£¼0.01).

¡¡¡¡The differences of mean deviation (MD), pattern standard deviation (PSD) and mean sensitivity among POAG with highly myopia and others were significant(P£¼0.05). Mean sensitivities in normal control group were higher than other three groups£¨P<0.05£©, and the MD, PSD were less than the others£¨P<0.05£©.For the highly myopia without POAG group, POAG with nonª²highly myopia group, and POAG with highly myopia group, the mean sensitivities decreased£¨P<0.05£©, and the MD and PSD increased accordingly£¨P<0.05, Table 1£©.

¡¡¡¡When compared with the normal control group¬ðs the RNFL thickness at every sectors of the POAG with highly myopia group, the POAG with highly myopia group and the highly myopia without POAG group decreased£¨P£¼0.05, Table 2). The RNFL thickness at superior and inferior sectors between the POAG with nonª²highly myopia group and highly myopia without POAG group were significantly different (P<0.05); but there were not significantly different at nasal and temporal sectors for these two groups. Compared with the POAG with nonª²highly myopia group and the highly myopia without POAG group, the RNFL thickness at four sectors of the POAG with highly myopia group were significantly decreasing£¨P£¼0.05£©.

¡¡¡¡In the association analysis we found there were negative correlation between PSD and RNFL thickness in every group, and positive correlation between mean sensitivity and RNFL thickness in corresponding four sectors£¨P <0.05£©.Among these the association between the mean RNFL thickness and PSD was the most distinct (Table 3).

¡¡¡¡DISCUSSION

¡¡¡¡The present studies revealed that the morbidity rate of POAG in crowd over 40 years old was 1.76%, however it increased to 3.31% if the person suffering from myopia at the same time, and increases with the progress of myopia and age[3ª²5]. The fundus degeneration may result in variable visual field loss in highly myopia patients. Graveet al[6] reported that enlargement of the physiological blind spot, temporal defects and irregular defects were the common types for visual field loss for highly myopia eyes. It is difficult to distinguish the causes of the visual field loss when highly myopia combined with POAG, especially in the early stage. Our study evaluated the retinal structure by measuring the RNFL thickness with OCT, and analyzed its function by visual field examination, to provide effective evidences for POAG with highly myopia. The RNFL thickness we evaluated at superior inferior nasal and temporal sectors of normal control group were similar to what Liu et al[7] had reported: 140¡À11,140¡À10, 85¡À14,90¡À11 and 114¡À6m, also similar to RNFL histology. In our study compared with the normal control group¬ðs the RNFL thickness at every sectors of the POAG with highly myopia group, the POAG with highly myopia group and the highly myopia without POAG group decreased. The mean RNFL thickness and the thickness at four sectors in the POAG with highly myopia group decreased significantly when compared with POAG with nonª²highly myopia group; but we didn't find significantly different at nasal and temporal sectors for these two groups. Compared with the POAG with nonª²highly myopia group and the highly myopia without POAG group, the RNFL thickness at four sectors of the POAG with highly myopia group were significantly decreasing. The RNFL thickness decreased diffusedly in the POAG with highly myopia group. The RNFL thickness in the POAG with nonª² highly myopia group was thinner than that in highly myopia without POAG group, and there were also significant differences for the RNFL thickness in superior and inferior sectors for those two groups. Several researches [8,9] had verified that the larger never fibers which mainly distribute at the superior and inferior of optic are liable to be damaged. Accordingly the defect of RNFL may first occur in those areas, which are susceptive in diagnose of early glaucoma. However early defect of the RNFL may also turn up with diffused defects, which adjusted by IOP, blood supply, anatomy of sclera and sieve plate, besides the distribution of nerve fibers.

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