SELECT
  fld."RDB$FIELD_NAME",
  fld."RDB$DESCRIPTION"
FROM
  rdb$relation_fields fld
WHERE
  fld."RDB$SYSTEM_FLAG" = 0 AND
  fld."RDB$RELATION_NAME" = UPPER(:table_name)

IBSQL1.ExecQuery;
try
  LFldName := IBSQL1.FieldByName('RDB$FIELD_NAME');
  LFldDesc := IBSQL1.FieldByName('RDB$DESCRIPTION');
  while not IBSQL1.Eof do begin
    LStr := LFldName.AsString;
    LStr := LFldDesc.AsString;
    IBSQL1.Next;
  end;
finally
  IBSQL1.Close;
end;

SELECT
  fld.ЭRDB$FIELD_NAME",
  CAST(fld."RDB$DESCRIPTION" AS VARCHAR(256)) AS "RDB$DESCRIPTION"
FROM
  rdb$relation_fields fld
WHERE
  fld."RDB$SYSTEM_FLAG" = 0 AND
  fld."RDB$RELATION_NAME" = UPPER(:table_name)

const
  DefaultBlobSegmentSize = 16 * 1024;

procedure ReadBlob(hBlobHandle: PISC_BLOB_HANDLE; Buffer: PByte; BlobSize: Long;
                   GDSLibrary : IGDSLibrary);
var
  CurPos: Long;
  BytesRead, SegLen: UShort;
  LocalBuffer: PByte;
begin
  CurPos := 0;
  LocalBuffer := Buffer;
  SegLen := UShort(DefaultBlobSegmentSize);
  while (CurPos < BlobSize) do
  begin
    if (CurPos + SegLen > BlobSize) then
      SegLen := BlobSize - CurPos;
    if not ((GDSLibrary.isc_get_segment(StatusVector, hBlobHandle, @BytesRead, SegLen,
                             LocalBuffer) = 0) or
            (StatusVectorArray[1] = isc_segment)) then
      IBDatabaseError(GDSLibrary);
    Inc(LocalBuffer, BytesRead);
    Inc(CurPos, BytesRead);
    BytesRead := 0;
  end;
end;