"Ex officio" generally means "by virtue of one's office." But in Spanish and in the context of review by a judge, the expression "revisión de oficio" does not imply that a judge is acting "by virtue of his office," but rather that he is reviewing some aspect of a case "on his own motion," rather than at the petition of one of the parties. In the US a judge acting on his own motion is said to be acting "sua sponte." In that regard, "sua sponte" means "of one's own accord, voluntarily, on its own motion: the court took notice sua sponte that it lacked jurisdiction over the case" (Black´s Law Dictionary, 8th ed.)

Your text refers to a judge's "sua sponte review" of aspects not included in the appeal ("revisión de oficio en cuanto a los puntos no recurridos"). Here are some examples of how "sua sponte" is used in this context:

Thus, the argument that a court may not sua sponte review all documents submitted to it for review is simply not comprehensible. ...
books.google.com/books?isbn=1590318048...

In particular, such a complaint will not be subject to sua sponte review for the purposes of determining whether such a complaint should be dismissed under ...
www.ned.uscourts.gov/pom/orders/97-10.txt

Although we acknowledged a general rule against sua sponte review of unraised .... It is not clear that Rule 4 would justify sua sponte review of a defense ...
bulk.resource.org/courts.gov/c/F2/971/971.F2d.506.91-7014.html

A similar provision mandates sua sponte review of complaints by prisoners. See 28 U.S.C. 1915A(b)(1). The district court did not rely on 1915A, ...
bulk.resource.org/courts.gov/c/F3/246/246.F3d.1278.00-2152.html

We conclude that an overall goal of avoiding unrequested court involvement does not remove a probate court's authority to sua sponte review probate ...
caselaw.findlaw.com/scripts/getcase.pl?court=co&vol=2003app%5C3737&invol=1

the proposition that the Court frequently engages in sua sponte review of ... position that this was an example of sua sponte review in his dissenting ...
www.aopc.org/OpPosting/Supreme/out/J-89-2005co1.pdf

The court again conducted a sua sponte review and dismissed on ... After Dr. Novosad did so, the court conducted a third sua sponte review. ...
ca10.washburnlaw.edu/cases/1998/04/97-2331.htm

In that decision, the court of appeals undertook sua sponte review of Petitioner .... However, when opting to exercise the power of sua sponte review, ...
65.45.99.70/opinions/opinion.cfm?OpinionID=6145

On 6 June 2001, the district court conducted a sua sponte review of the entire record and dismissed the consolidated cases. The district court noted that ...
www.assetprotectionbook.com/FL_Farese-Scherer_2003.htm