INTRODUCTION TO OPTHALMIC LENSES

Introduction to Ophthalmic Lenses

Introduction to Ophthalmic Lenses

If the lens is dispensed with a +2.00DS base curve calculate both accurately and approximately the sag height if the centre thickness is 2mm and is made from a refractive index of 1.496 and the lens size is a 52mm round eye? What is the percentage difference between the two results?

An ophthalmic lens element (100) for correcting myopia in a wearer's eye is disclosed. The lens element (100) includes a central zone (102) and a peripheral zone (104). The central zone (102) provides a first optical correction for substantially correcting myopia associated with the foveal region of the wearer's eye. The peripheral zone (104) surrounds the central zone (102) and provides a second optical correction for substantially correcting myopia or hyperopia associated with a peripheral region of the retina of the wearer's eye. A system and method for dispensing or designing an ophthalmic lens element for correcting myopia in a wearer's eye is also disclosed.

GCA is the most common form of systemic vasculitis in adults over the age of 50 years. There is considerable overlap with PMR, a related disease. Extracranial artery involvement, especially of the aorta and its branches, is not uncommon. Typically, large- and medium-sized arteries are affected: the eyes' ciliary arteries, being so tiny, are among the small arteries thus affected. Classic symptoms such as headache, jaw claudication and tenderness in the temporal region usually appear prior to the onset of ocular manifestation. Cranial ischaemic complications, in particular visual loss, mainly due to anterior ischaemic optic neuropathy (AION) or central retinal artery occlusion (CRAO) are the most feared ophthalmological sequelae of GCA. The incidence of ocular manifestation is generally estimated at ~30%.

Visual ischaemic complications are frequently preceded by amaurosis fugax constituting a prodromal signal before permanent loss of vision appears. Another ocular manifestation is diplopia due to ischaemia of the extraocular muscles or brain stem.

What is the percentage reduction in edge thickness if the lens size is reduced to a 46mm round eye?

An ophthalmic lens element according to the present invention includes a front surface (that is, the surface on the object side of the lens element) and a back surface (that is, the surface nearest the eye). The front and back surfaces are shaped and arranged to provide the respective optical corrections. In other words, the front and back surfaces are shaped and arranged to provide a refracting power for the central zone and the peripheral zone respectively.

In this specification, the refracting power provided by the central zone will be referred to as "the central zone power", whereas the refracting power provided by the peripheral zone will be referred to as "the peripheral zone power". The central zone refracting power substantially corrects myopia associated with foveal region, whereas the peripheral zone refracting power substantially corrects myopia (or hyperopia) associated with the peripheral region.

According to the figure, Astigmatism is a non-spherical refractive error and can exist along with myopia or ...