C# Definition:

    [StructLayout(LayoutKind.Sequential)]
    public struct IMAGE_OPTIONAL_HEADER32
    {
        //
        // Standard fields.
        //
        public UInt16   Magic;
        public Byte     MajorLinkerVersion;
        public Byte     MinorLinkerVersion;
        public UInt32   SizeOfCode;
        public UInt32   SizeOfInitializedData;
        public UInt32   SizeOfUninitializedData;
        public UInt32   AddressOfEntryPoint;
        public UInt32   BaseOfCode;
        public UInt32   BaseOfData;
        //
        // NT additional fields.
        //
        public UInt32   ImageBase;
        public UInt32   SectionAlignment;
        public UInt32   FileAlignment;
        public UInt16   MajorOperatingSystemVersion;
        public UInt16   MinorOperatingSystemVersion;
        public UInt16   MajorImageVersion;
        public UInt16   MinorImageVersion;
        public UInt16   MajorSubsystemVersion;
        public UInt16   MinorSubsystemVersion;
        public UInt32   Win32VersionValue;
        public UInt32   SizeOfImage;
        public UInt32   SizeOfHeaders;
        public UInt32   CheckSum;
        public UInt16   Subsystem;
        public UInt16   DllCharacteristics;
        public UInt32   SizeOfStackReserve;
        public UInt32   SizeOfStackCommit;
        public UInt32   SizeOfHeapReserve;
        public UInt32   SizeOfHeapCommit;
        public UInt32   LoaderFlags;
        public UInt32   NumberOfRvaAndSizes;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
        public IMAGE_DATA_DIRECTORY[] DataDirectory;
    }

VB Definition:

User-Defined Field Types:

IMAGE_DATA_DIRECTORY

Notes:

Comments are from WinNT.h