The variation of accommodation with age

It is seen that in the early year of the amplitude of accommodation is about 14 D and that the near point is situated at 7 cm distance. Thereafter it gradually and uninterruptedly recedes at the age of 36 it has reached 14 cm, when the amplitude of accommodation has become halved and is now 7 D instead of original 14 D. At the age of 45 it has reached 25 cm, and the amplitude of accommodation is only 4 D; at the age of 60 only about 1 D of accommodation remains.

            In most of the cases near work is done at an average distance of 28 to 30 cm away from the eyes, and therefore in the emmetrope the actual limit of clear vision is reached at 45 years when an amplitude of 3.5 to 4 diopters of accommodation remains. This however would entail working at the near point continuously and thus exercising the whole of the accommodation to obtain useful vision a condition of strain that can rarely be tolerated over any length of time. Comfort demands that about one-third of the4 accommodation be kept in reserve, so that when this limit has been reached and the near point is at a distance of 22 cm presbyopia may be said to have set in. In the emmetrope this occurs between 40 and 45 years of age, although there is some geographical, perhaps racial variation: an earlier age of onset may occur in those living in the tropics. Thereafter the accommodation must be supplemented by a convex lens if near work is to be done without strain.

            A hypermetrope starts life with this near point considerably further away than that of an emmetrope so that the symptoms of presbyopis will come on earlier. Thus a hypermetrope with an error of +3 D will require exercise 7 D of accommodation to give himself an amplitude of 4 D; he may therefore show presbyopic symptoms at about 25 years of age. In a myope, on the other hand, the opposite conditions hold, and if he has an error of – 4 D presbyipia will never occur.

            Presbyopia is thus a relative term, depending not only on the age but also on the refraction. It also varies with the individual and with his habits. A person who has the habit of reading with his book on his knees complains of discomfort later than one who is used to reading more closely; and the carpenter or the book-keeper or the musician will be comfortable at his work at 30 or 35 cm or over, while the seamstress or the compositor or the engraver of the same age and with the same refractive state will have been forced to use spectacles in order to see at his working distance of 20cm. Or again, the ciliary muscle may fail in states of debility or disease and the physiological accommodation be at fault. There is thus no fixed presbyopic point, and there can be no rational rule-of-thumb treatment.


                                                                                                                       Reference:- Duke-elder's Practice of refraction tenth edition

                                    

High definition contact lens

A rocking high definition lens in Indian contact lens market 

It is a great experience for us that Bausch & lomb comes up with a soft daily disposable lens in Indian market. This is the same very lens which is being waited by all Indian contact lens wearer. This lens is a very good lens for all those who want to see the world sharp even in low light condition. The design of this lens is based on advance aspheric optics.

We need this lens because in Indian contact lens industry no lens can eliminate spherical aberration. The vast majority of contact lenses in today’s market are mass-produced, cast molded or one day disposable lenses, to achieve aberration control on these lenses, Manufacturer must make approximations for the general population’s higher order distortions.

As we know that spherical aberration is the failure of a lens to form a point image of a point object on the retina. It is directly proportional to aperture of lens/pupil. Bigger size pupil creates more spherical aberration than smaller.

So that an overall improvement in retinal image with an aberration controlled HD design contact lens should be there.

If a customer has been wearing contact lens for most of his/her life and have tried lots of lenses in the past with unpleasant results. HD optics daily disposable lens may provide the answer he/she has been looking for. Because these lenses are designed specially to reduce aberrations even the pupil size is relatively bigger.

HD daily disposable contact lenses are a great option to those who wants to reduce halos while driving at night. It enhances contrast; due to this, wearers can see every detail of objects sharp and distinctly.

HD daily disposable contact lens is better for those who want to wear contact lenses for long time. Because wearing contact lenses too long time can cause discomfort and damage to the eyes. It mostly occurs when debris or foreign bodies have become detained between cornea and lens. Due to this corneal vascularisation may be possible.

But with the ongoing advances in the technology Bausch and lomb has gone through a wide range of changes and upgrades in contact lens in India and comes up with soft lens daily disposable high definition lenses which is being designed with comfort moist technology; providing unsurpassed comfort to contact lens wearers. Soft lens daily disposable high definition lens comes with poloxamine coat on the lens which acts as a conditioning ingredient that attracts moisture and work with tears, enveloping the entire lens in a cushion of moisture.

 HD daily disposable contact lenses also benefit those who spend a great deal of time in front of computer as they facilitate vision correction and eye movement.

After giving this lens to my patrons I feel proud because, earlier they used to face such type of problems like grainy, fuzzy vision associated with previous contact lenses, blurry vision and uneasiness, reading inability in low light condition, but no longer now.

In one word I would like to say on the behalf of my customer, after wearing convenient and hassle-free HD soft lens daily disposable contact lenses.” WE HAVE NEVER SEEN SUCH TYPE OF CRISP, CLEAR AND COMFORTABLE VISION BEFORE”.  

crisp vision requirement

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