FIELD OF THE INVENTION The present invention relates to the pharmaceutical sciences. The present invention provides the sterilization process of an ophthalmic composition which comprises timo1o1 or salt thereof optionally with pharmaceutically acceptable agent(s), wherein the sterilization is 1 0 achieved through aseptic filtration technique. Further the present invention provides the sterilization process by optimising the process parameters by varying the heating time at a temperature to control the viscosity of the ophthalmic composition of present invention through aseptic filtration technique wherein the filtration is done under aseptic condition through 0.45~tm clarification pre-filter follmved by 15 0 2 ~t sterilizing grade filter. The process is simple and economicaL BACKGROUND AND RELEVANT ART Drug sterility is crucial in the pharmaceutical industry for sterile products like in Ophthalmic and production of a sterile ophthalmic pharmaceutical product is often a 20 technically challenging task. Regulatory bodies suggest that "whenever possible products intended to be sterile should be terminally sterilized by heat in their final container and where it is not possible to carryout terminal sterilization by heating due to the instability of a formulation or incompatibility of a pack type (e.g. plastic eye-dropper bottles), an alternative method for sterilization should be considered". 25 Sterilization can be achieved by the use of other techniques like moist or dry heat, by irradiation with ionizing radiation, by ethylene oxide (or other suitable gaseous sterilizing agents), or by filtration with subsequent aseptic filling of sterile final containers. Each method has its advantages and disadvantages. Moist heat I Steam sterilization like autoclaving or in-situ heating of viscous ophthalmic 30 dosage forms is common practice in pharmaceutical industry to make the product sterile. It involves heating the ophthalmic solution or suspension, to be sterilized, at 121 oc for about 15- 20 minutes. However, in many cases it is not advisable due to heat sensitivity of the drug or excipients, incompatibility of excipients with drug at higher temperature and the overall cost wo 2021/198911 PCT/IB2021/052635 2 involved. Additionally, in the case of a viscous pharmaceutical formulation, heat often alters the physical attributes of the formulation like appearance, viscosity by altering the properties of the polymer used. Further, ophthalmic solutions containing heat stable polymers may be manufactured by 5 using aseptic techniques. In these techniques, the polymer solution is prepared separately and then is sterilized by autoclaving. Active ingredient and other ingredients may be dissolved in \Vater for injection and filter sterilized. The polymer solution and active ingredient solution were mixed and volume will be made up aseptically. This process is very complex and there is always high risk of sterile operations. 10 15 US4861760 discloses a pharmaceutical composition intended for contacting with a physiological liquid characterized in that said composition is intended to be administered as a non-gelled liquid form and is intended to gel in situ, this composition containing at least one polysaccharide in aqueous solution, of the type which undergoes liquid-gel phase transition gelling in situ under the effect of an increase in the ionic strength of said physiological liquid. W02000035439Al provides a process of manufacturing of formulation of topical beta blockers with improved efficacy and wherein the final product is autoclaved and put into a sterile packaging. \Vhile working on the development of timolol ophthalmic gel forming solution dosage form, the present inventors have embarked upon a simple technique, which eliminates the 20 Steam sterilization or autoclaving of ophthalmic dosage forms to make the product sterile. It was surprisingly found that aseptic filtration of the solution for ophthalmic administration comprising timolol or salt thereof, most preferably, the timolol maleate and one or more pharmaceutically acceptable agents can impmt the same sterility to the ophthalmic dosage form as that obtained with steam sterilization, autoclaving and/or aseptic mixing, 25 wherein the filtration is done under aseptic condition through 0.45~tm clarification pre-filter followed by 0.2~t filter. The novelty lies in the sterilization process through aseptic filtration technique and for that inventors have optimise the process parameters by varying the heating time at a temperature to control the viscosity of the ophthalmic composition of present invention and accordingly the filtration is done under aseptic condition through 0.45!1m 30 clmification pre-filter followed by 0.2~ sterilizing grade filter. wo 2021/198911 PCT/IB2021/052635 3 OBJECTS OF THE INVENTION The main object of the present invention is to provide the sterilization process by optimising the process parameters and by varying the heating time at a temperature to control the viscosity of the ophthalmic cornposition through aseptic filtration technique, vvherein the 5 filtration is done under aseptic condition through 0.45~tm clarification pre-filter follmved by 10 02~t sterilizing grade filter. Another object of the present invention is to provide the sterilization of an ophthalmic composition comprising timolol or salt thereof optionally with pharmaceutically acceptable agents wherein the sterilization is achieved through aseptic filtration technique. Another object is to provide the sterilization process of ophthalmic composition of present invention through aseptic filtration technique wherein the filtration is done under aseptic condition through 0.45~tm clcu-ification pre--filter followed by 0.2~ sterilizing grade filter. Another object of the present invention is to provide an aseptically fi1led ophthalmic 15 composition comprising timolol or salt thereof optionally with pharmaceutically acceptable agents, wherein the said composition is intended to be administered as a non-gelled liquid form and is intended to gel in situ after the administration. Yet another object of the present invention 1s to provide the pharmaceutical compositions, in particular, the ophthalmic compositions and drug delivery vehicles which me 20 adrninistrab]e as liquids and gel upon contact with the eye. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1: Flow diagram of a process to prepcu-e timolol gel forming solution sterilized by aseptic filtration technique. 25 Figun~ 2: Effect of heating temperature and time on the viscosity of present composition. The details are presented below: Trial Heating temperature & Viscosity (in cps) Time Trial-1 121 oc for 20 mins 114.7 Trial-2 121 oc for 20 mins 146.9 5 wo 2021/198911 PCT/IB2021/052635 4 1 00°C for 60 mins 410 Trial-3 100°C for 120 mins 271 1 00°C for 180 mins 243 1 00°C for 240 mins 226 Trial-4 110°C for 150 mins 58.35 Trial-5 110°C for 120 mins 102.9 Figure 3: Viscosity comp