how is eyesight measured

{"cid":"91190363","title":"VT-5E Handheld Phoropter , Ophthalmic Equipment Precision Measurement","imgUrl":"https:\/\/img.chinax.com\/nimg\/4d\/20\/9cda117423c92de39765fb9a322d-200x200-1.jpg","attrs":{"Price":"Negotiable","Brand Name":"KESHILONG","Model Number":"GD8701","Minimum Order Quantity":"1pcs","Delivery Time":"10-20 work days","Certification":"CE, FDA","Place of Origin":"China","Payment Terms":"L\/C, T\/T, Western Union","Supply Ability":"300pcs\/month","Color":"Black or White for option","Quality":"Top-grade quality","Sphere powers":"+16.75D to-19.00D","Cylinder power range":"0 to-6.00D","Astigmatic axis scale":"0 to 180\u00b0 in 5\u00b0 steps","Cross cylinder":"\u00b10.25D","Rotary prism":"0 to 20D in 1D step","Forehead rest adjustment":"16mm backward and forward"}}

{"cid":"91193398","title":"High Accuracy Eye Examination Instruments Can Be Connected With Slit Lamp","imgUrl":"https:\/\/img.chinax.com\/nimg\/5f\/93\/4100b7ef0061d2fd395b07ee1337-200x200-1.jpg","attrs":{"Price":"Negotiable","Brand Name":"66 VISION"}}

{"cid":"91226155","title":"Golden Vision Eye Patches in a 30-Pouch Green Box for Wholesale","imgUrl":"https:\/\/img.chinax.com\/nimg\/9b\/6b\/d030aaba5dbef8c421039178f2f2-200x200-1.jpg","attrs":{"Price":"CNY 19.80 per 30-pouch box; excludes tax and freight","Brand Name":"YISHIYUAN","Model Number":"30 Pouches per Box","Minimum Order Quantity":"1000 boxes","Delivery Time":"Confirmed after order and artwork review","Unit Packaging":"Individually sealed pouch","Packaging Details":"30 individually sealed pouches per dark-green retail box; box 10 x 5 x 14.2 cm (W x D x H). Source-listed carton: 68 boxes, 28 x 35 x 66 cm; confirm final shipment.","Retail Box Dimensions":"10 x 5 x 14.2 cm (W x D x H)","B2B Website Price":"CNY 19.80 per 30-pouch retail box","Payment Terms":"T\/T","Source-listed Carton Quantity":"68 retail boxes per carton","Place of Origin":"Hubei, China","Product Format":"External eye-area patch","Unpacked Item Dimensions":"? cm; item and pouch measurement layers pending","Retail Quantity":"30 pouches per box","SKU Identity":"Dark-green 30-pouch version","Retail Package Color":"Dark green","Supply Ability":"Confirmed according to order quantity","Source-listed Carton Dimensions":"28 x 35 x 66 cm; confirm final shipment"}}

{"cid":"91210102","title":"OEM 10 Inch Electronic LCD Writing Board Erasable Writing Pad for kids","imgUrl":"https:\/\/img.chinax.com\/nimg\/35\/b4\/1ba8b862f9308ce3f439a9a5cf36-200x200-1.jpg","attrs":{"Price":"$ 1.85 PCS","Brand Name":"Ikinor","Model Number":"IK10","Minimum Order Quantity":"1000 PCS","Delivery Time":"20-30 work day","Certification":"CE\/RoHS\/FCC","Place of Origin":"China","Payment Terms":"T\/T, MoneyGram, Western Union, L\/C, D\/A, D\/P.","Supply Ability":"50000 PCS\/month","Packaging Details":"Packing: Box Package,Single package size: 236X170X6 mm","Panel Size":"10 Inches","Color":"Orange,Pink,Blue,White","Material":"LCD + ABS","Feature":"Loose Leaf","Battery":"No","Weight":"700g","Packing":"Box Package","Application":"Office,Home, School"}}