You can also set background is transparent. So the button looks like fit your icon.
<ImageButton
android:id="@+id/Button01"
android:scaleType="fitcenter"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:cropToPadding="false"
android:paddingLeft="10dp"
android:background="@android:color/transparent"
android:src="@drawable/eye" />