| High myopia is also called pathological myopia or degeneration m; opia. 3-6% of all myopia is high myopia. It makes a lot of difficulties to peopli 's daily life, including blindess. After studies of more than 200 years, there is still n i satisfactory explanation to myopia pathogenesis. More and more studies prozed that not modulation but the function and activity of nerve cell in the retila played an important role in the form deprivation myopia (FDM). At present, it is known that many kinds of neurotransmitters in the retina are concerned with the growth of eyeball and improve the development of FDM. In the past several years, many studies had indicated that nitric oxide (NO) participate in the development of IDM, but the particular mechanism was not clear. It was reported that the superoxi :le dismutase (SOD) activity in the retina-retinal pigment epithelium (RPE)-choroid of chick with FDM declined. But whether a great deal of free radical occur in FDM is not clear. It was reported that apoptosis existed in the retina of pathological myopia but whether this phenomenon occurs in FDM is not clear. We established the ch ck model of FDM and selected biochemical assays, morphological observation and TUNEL technique to study the relationship between NO , free radical, apoptosis and FDM. Meterials and Methods 1 . 80 male hailen chicks were selected and were randomly divided into 4 groups. Allthe right eyes underwent form deprivation with translucent goggles, and the left eyes were used as control. After the right eyes were randomly covered for 7, 14, 21 , 28 days, the refractive state was respectively determined by means of streak retinoscopy (without cycloplegia). Extracted the eyes and measured the axial length and equatorial diameter with vernier caliper. Got specimens of retina-retinal pigment epithelium (RPE)-choroid and then homogenized them. Insoluble material was removed from the homogenized material by centrifugation at 3500 rpm for 20 minutes, the supernatant was used for measurment of the activity of nitric oxide synthase (NOS ) and SOD, and the content of malonyldialohyed (MDA). 2. 20 male hailen chicks were selected. All the right eyes underwent form deprivation with translucent goggles, and the left eyes were used as control. 1 week later, removed the goggles and determined the refractive state by means of streak retinoscopy (without cycloplegia). Then extracted the eyes and measured the axial length and equatorial diameter by vernier caliper, after routine fixation, dehydration, paraffin embedding, Sum paraffin sections were taken. Rutine hematoxylin-eosin (HE) staining, detected the morphological changes in form deprived chicks retina and sclera under light microscope. TUNEL techque was used to study the apoptosis of nerve cells in the retina. Results1. Biochemical assays: (1) Monocular deprivation could lead to develepment of myopia: The refractive state, axial length and equatorial diameter showed significant difference between the covered eyes and the control eyes (p < 0.05). The longer the eyes were covered, the more severe the myopia was, and there was significant difference among groups at different time. (2) Activity of i-NOS (U/mg prot) indicated: after being covered for 7, 14, 21, 28 days, the activity of i-NOS in the covered eyes was 0.35 ±0.02, 0.33±0.02, 0.32±0.02, 0.29 ± 0.02, respectively; the activity of i-NOS in the control eyes was 0.39±0.02, 0.37±0.03, 0.39 ± 0.02, 0.37 ± 0.03, respectively. The activity of i-NOS in the covered eyes was lower than the control after the same period of covering time (p < 0.05). The longer the eyes were covered, the lower the activity of i-NOS was. (3) Activity of total NOSindicated: there was no difference of total NOS between the covered eyes and the control (p > 0.05). (4) Content of MDA (nmol/mg prot) indicated: after being covered for 7, 14, 21 , 28 days, the content of MDA in the covered eyes was 1.52 ± 0.29, 1 .64 ± 0.21 , 1 .97 ± 0.22 , 1 .93± 0.27, respectively; in the control eyes was 1.30 ± 0.
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