No, it does not invalidate the fast.
عَنْ عَائِشَةَ، قَالَتْ اكْتَحَلَ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ وَهُوَ صَائِمٌ
“Sayidah Aisha narrated, ‘The Messenger of Allah ﷺ applied kohl to his eyes while he was fasting.’ (Sunan Ibn Maja, 1678).
عَنْ بَرِيرَةَ، مَوْلَاةِ عَائِشَةَ، قَالَتْ: «رَأَيْتُ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ يَكْتَحِلُ بِالْإِثْمِدِ وَهُوَ صَائِمٌ»
Bareera, the Mowlaat of Sayidah Ayesha said, ‘I saw the Messenger of Allah applying Ithmid (Kohl) whilst he was fasting.’ (Al-Mujam al-Owsat, Hadith 6911).
عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّهُ كَانَ يَكْتَحِلُ وَهُوَ صَائِمٌ
“It is narrated from Anas, that he used to apply Kohl whilst fasting.” (Sunan Abi Dawood, 2378).
There are numerous narrations establishing the fact that the Prophet ﷺ used Kohl whilst fasting, and certain Sahabah done this too. For a discussion regarding the authenticity of these narrations please see the link below.
Due to this evidence Hanafi scholars said using eye drops does not invalidate the fast, even if one senses the taste of it in the throat.
قلت أَرَأَيْت الصَّائِم يكتحل بالإثمد والذرور وَالصَّبْر وَغَيره قَالَ نعم لَا يضرّهُ ذَلِك شَيْئا قلت فَإِن وجد طعمه فِي حلقه قَالَ وَإِن وجد طعمه فِي حلقه (كتاب الأصل المبسوط )
I said, if a fasting person used Ithmid, Dharoor, Sabr or other Kohl (what is the ruling)? He (Imam Abu Hanifah) said, there is no harm in this at all. I said, even if he senses the taste in his throat? He said (yes) even if he senses the taste in his throat (the ruling is the same). (Imam Muhmad Shaybani, al-Asl).
ولا بأس بالكحل للصائم وإن وجد طعمه (فتاوى قاضيخان)
There is no harm in a fasting person using Kohl, even if he senses the taste of it in his throat. (Fatawa Qadi Khan).
وَلَوْ أَقْطَرَ شَيْئًا مِنْ الدَّوَاءِ فِي عَيْنِهِ لَا يُفْطِرُ صَوْمَهُ عِنْدَنَا، وَإِنْ وَجَدَ طَعْمَهُ فِي حَلْقِهِ (الفتاوى الهندية)
And if he drips medicine into his eye then his fast will not be invalidated according to us (the Hanafi Madhab), even if he senses the taste in his throat. (al-Fatawa al-Hindiya).
وَالِاكْتِحَالُ لَا يَضُرُّ الصَّائِمَ، وَإِنْ وَجَدَ طَعْمَهُ فِي حَلْقِهِ (المبسوط)
And using Kohl does not harm the fasting person, even if he senses the taste in his throat. (Imam al-Sarakhsi, al-Mabsoot).
(أَوْ أَدْهَنَ أَوْ اكْتَحَلَ أَوْ احْتَجَمَ) وَإِنْ وَجَدَ طَعْمَهُ فِي حَلْقِهِ
(قَوْلُهُ: وَإِنْ وَجَدَ طَعْمَهُ فِي حَلْقِهِ) أَيْ طَعْمَ الْكُحْلِ أَوْ الدُّهْنِ (رد المحتار على الدر المختار)
Imam al-Haskafi: Or if he uses oil, or Kohl or has blood cupping done (the fast will remain valid). Even if he senses the taste in his throat.
Imam Ibn Abideen: His saying, Even if he senses the taste in his throat, is referring to the taste of Kohl or oil. (Radd al-Muhtaar).
In recent times certain Hanafis have started to oppose this ruling. They claim that the ruling that has been mentioned in classical Hanafi works is based on medical knowledge of that time. They argue that modern medical science has proven that using eye drops leads to them entering the stomach, therefore we should oppose the ruling in the books of the Madhab and say eye drops do invalidate the fast.
Had this claim been accurate then it could be considered, but there is a fundamental flaw in it. The ruling in the books of Fiqh is not based on medical science rather it is based on Hadith, therefore modern medical science has no role to play regarding this ruling. It is a matter of Hadith narrations and discussion should be focused on such narrations, not previous and recent medical knowledge. This is a clear error and such Hanafis are required to reconsider what they have promoted.
Since the premise is false, the ruling is incorrect. Had these Hanafis claimed that the Hadith narrations above are weak, then that would be a valid discussion to have. However, many of them completely ignore the Hadith and move on to medical science, this is an incredible oversight. In any case, the narrations are sound when combined and further information can be found in the link below.
And Allah (Most High) Knows Best.
– Answered by Shaykh Noorud-deen (28.04.2021)
The authenticity of the Kohl Hadith
See also (video):