today I will discuss about Feb and same rules in contact lens the meaning of Feb and Sam is Feb means flutter add Plus same means steeper at minus in contact lens practice our objective is to get optimal feet of contact lens fitting but if the feet is stiffer fit than optimal fit we have to add minus power to the contact lens prescription and if the feet is flatter fit than the optimal fit we have to add plus power to the contact lens prescription you might be thinking why do we need to add minus or plus power to the contact lens prescription if the feet is steeper or flatter let's see in the next slide for steeper feed we add minus power and for flatter feed we add plus power to the contact lens prescription so that patient's visual Acuity doesn't become affected now again you might be thinking how can steeper and flutter fit affect the visual equity to understand this first you need to know what is TR lens the teards accumulate between the back surface of contact lens and anterior surface of cornea acts as a lens which is called Tear lens here in this figure this is cornea this is contact lens and the tears accumulate between posterior surface of contact lens and anterior surface of cornea is called Tear lens if the contact lens is cheap fit then the space between the cornea and contact lens is more at the center than periphery which acts as a convex lens this is an example of stiff contact lens fitting this is cornea this is contact lens due to strip fit the space between the contact lens and cornea is more at the center and the space between the contact lens and cornea at periphery is less due to which a convex Tire lens is formed and if the contact lens feet is flat feet then the space between the cornea and contact lens is less at Center and more at Fairfield which acts as a concave lens this is an example of flat feet of contact lens here this is cornea this is contact lens and the space between the contact lens and cornea is less at the center and the space between the contact lens and cornea is more at periphery due to which a concave to your lens is formed so in stiff fit due to formation of convex tear lens rays will focus in front of the retina and patient will become myopic and in flat feet due to formation of concave tear lens rays will focus behind the retina and passion will become hypermetropic which will affect the visual Acuity of the patients that's why for steeper fit we add minus power and for flatter feed we add plus power to the contact lens prescription so that patients visual Equity doesn't become affected now another cushion arrives if the feet is stiff or flat then we can change the parameters and get optimal fit white Feb and same rule let's see in the next slide sometimes for better stability of contact lens especially rigid gas permeable contact lens we need steeper fit than optimal fit even with the optimal fit few patients may feel discomfort with the contact lens we can go for flatter fit in Charge cases so in such cases we need Feb and same rules so that the patient's visual Equity doesn't become affected so the overall summary is to get steeper fit we will increase actual crediting and decrease the power of contact lens prescription so that patients visual Equity doesn't get affected and to get flatter fit we will decrease actual carrying and increase the power of contact lens prescription so that patients visual Equity doesn't get affected [Music] foreign [Music] [Music] stay with smart Optometry and study Optometry smartly foreign [Music] [Music] foreign foreign [Music]