Unknown impurities were detected during Photo degradation of Olopatadine Hydrochloride ophthalmic solution 0.5% (w/v) when analyzed using the High performance liquid chromatographic technique with Photo Diode Array Detection. For further investigation was carried out by isolating these impurities from impurity rich sample of Olopatadine Hydrochloride ophthalmic solution 0.5% (w/v) using preparative isolation technique. The Olopatadine Hydrochloride ophthalmic solution 0.5% (w/v) was subjected to photolytic forced degradation in the presence of Benzalkonium chloride and other excipients like Hypromellose, Mannitol, Hydroxypropyl, Boric acid, Kollidon 30 LP and mixture of solvents (Acetonitrile: Methanol; 1: 1 (v/v) under Ultra violet visible light. This led to the formation of the said impurities in higher concentration. This sample was then subjected to preparative HPLC for isolation of these unknown impurities. The structure of these unknown impurities was further elucidated using a different technique like Infra Ray Spectroscopy, Direct infusion (DI) Mass Spectroscopy, Ultra violet-Visible Spectroscopy, Proton Nuclear Magnetic Resonance Spectroscopy, carbon Nuclear Magnetic Resonance and Distortionless Enhancement by Polarization Transfer (DEPT) Spectroscopy which helped to confirm the structure of the impurities. Structure elucidation of the two impurities revealed that these are E and Z isomers of the Olopatadine hydrochloride Carbaldehyde. Olopatadine Z-isomer is used in the formulation of the Olopatadine Hydrochloride Ophthalmic Solution 0.5% (w/v). The minor amount of E-isomer also remains present in this solution as a potential impurity. However, the amount of E-isomer may increase in the solution form due to racemization. Hence, the respective Carbaldehyde impurities (both E and Z isomers) are forming during Photolytic degradation. This formation is happening through photolytic Norrish type-1 reaction which is elaborated in the paper.