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Related Party Disclosures - Additional Information (Details) - USD ($)			12 Months Ended
	Sep. 19, 2024	Aug. 28, 2023	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Disclosure of transactions between related parties [line items]
Amount due to related party, interest expense			$ 32,793,000	$ 24,699,000	$ 13,462,000
Consultancy Agreement [member]
Disclosure of transactions between related parties [line items]
Transaction costs paid			$ 275,000	$ 125,000
Top of Range | Consultancy Agreement [member]
Disclosure of transactions between related parties [line items]
Provision of services	$ 275,000	$ 300,000
Ocelot
Disclosure of transactions between related parties [line items]
Amounts owed to related party, effective rate			23.00%

X

- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

+ References

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amounts owed to related party, effective rate.

+ References

No definition available.

+ Details

Name:	opt_AmountsOwedToRelatedPartyEffectiveRate
Namespace Prefix:	opt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Interest expense related party transactions.

+ References

No definition available.

+ Details

Name:	opt_InterestExpenseRelatedPartyTransactions
Namespace Prefix:	opt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

provision of Services

+ References

No definition available.

+ Details

Name:	opt_ProvisionOfServices
Namespace Prefix:	opt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Transaction costs paid.

+ References

No definition available.

+ Details

Name:	opt_TransactionCostsPaid
Namespace Prefix:	opt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

Name:	ifrs-full_ServiceConcessionArrangementsAxis=opt_ConsultancyAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=opt_OcelotMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: