Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 
  • Users Online: 4509
  • Home
  • Print this page
  • Email this page

   Table of Contents      
ARTICLES
Year : 1983  |  Volume : 31  |  Issue : 6  |  Page : 799-800

Beneficial effects of myopia


AMU Institute of Ophthalmology, Aligarh, India

Correspondence Address:
J Nath
AMU Institute of Ophthalmology, Aligarh
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


PMID: 6676271

Rights and PermissionsRights and Permissions

How to cite this article:
Nath J. Beneficial effects of myopia. Indian J Ophthalmol 1983;31:799-800

How to cite this URL:
Nath J. Beneficial effects of myopia. Indian J Ophthalmol [serial online] 1983 [cited 2020 Jun 5];31:799-800. Available from: http://www.ijo.in/text.asp?1983/31/6/799/29330

Simple Myopic eye is superior to the em­metropic and the hypermetropic eye aestheti­cally, medically, socially and even technically. It is prominent with a large palpebral aper­ture, a large cornea and is simply beautiful.

Presbyopia, and early affliction in emmet­ropes and hypermetropes, appears late or not at all in simple myopes.

They suffer less from diabetic retinopathy. Jain observed that it is either less frequent, or if present, progresses more slowly in myopes. This observation was also made by Gonzales 2and Amalrie(3). The former did not find a single case of high myopia in 146 cases of vascular le­sion while the latter found that the course of diabetic retinopathy is more benign in myopic eyes or does not occur at all. In a study4 carried outon Eaeles's disease at the Institute of Ophthalmology, Aligarh, it was found that simple myopes are comparatively rare suffer­ers from this malady, especially the higher ones.

Gonzales(2) also observed that hypertensive retinopathy is also less in myopes. In a similar study Kato(5) found that the A/V crossing change in hypertension were less marked in high myopes.

Glaucoma occurs less in these eyes due to the deep anterior chambers while cataract takes an unusually long time to mature. The glasses required after the operation are less bulky and hence is an added advantage to sim­ple myopes.

Papilloedoema due to increased intra cro­nial pressure is also less common in simple myopes. This was shown by Marchisanio(6),Biette(7) and Morone(8). Consequently, the dam­age to the optic nerve fibres is less or delayed.

The reason of these advantages are not dif­ficult to find if the evolution is considered.

The eye has passed through many phases of development. Diffuse sensitivity to light has been seen in Protozoa and Porifera. In inver­tebrates the most important fact, barring a few exceptions, is that the eye has developed from ectoderm while in Chordates the eye has de­veloped from neurectoderm.

In Coelentrata, contact photoreceptors of the most elementarry types are present. The Echinodermata, have a photosensitive skin while the star fish have the optic cushions. The Platyhelmenthes have developed the rudimentary sense organs and in the Annelida the receptors are distributed in the epithelium and around the sub epithelial nerves. Molluscs have two cephalic eye which subserve the vis­ual functions while the Arthropodes show a wide variation of eyes is simple, compound and even a median eye.

In the case of vertebrates, the eyes have ari­sen from the neurectoderm. The strangeness is the sudden appearance of the eye which later underwent a number of changes to suit diffe­rent functions.

In fishes the eye is relatively much more hypermetropic as they surface in water. The shape of the eye is streamlined to facilitate swimming. The lens moves forwards and back­wards in order to focus the prey.

Eyes, of Amphibia, are no longer stream­lined but spherical. They also move the lens forward and backwards to accommodate. To survive, their objectives are limited. To mois­ten the eye the Marderian glands and the nasolacrimal ducts appear. Reptiles have a mobile iris and accommodate by deformation of the lens. Avians have good vision a well de­veloped eye with nasal accentricity to help in a little binocular function but they must have a wide field to survive.

Accommodation or focussing of the eye at various distances is very important and has been achieved by various developmental ac­quisitions in different animals. There is the de­velopment of accessory retinae close to the diopteric apparatus (as in the developmental of tubular eye in deep sea fishes.) Variations in the positions of the visual cell in relation to the lens (bats or horse), the use of stenoepic pupil (the cat), deformation by the muscular ap­paratus of the eye (lamprey), pushing and pul­ling of the lens forward and backward (some fishes, amphibia and snakes), change in shape by squeezing it (reptiles and birds) or relaxing it (mammals).

Wild animals and primates should see better at a distance as this helps both in location, at­tack and defence. Wild animals are therefore usually hypermetropic or emmetropic while domisticated animals show a considerable amount of myopia.

In man, the functional requirement of the eye has tremendously changed. The eye of the hunter and caveman required a good distance vision. Later man settled down to be tiller of the land, started cooking his own food and did much more near work than his forefathers did. As the need for near work increased, the fa­culty of convergence, a comparatively recent acquirement on the evolutionary scale, has de­veloped. This facilitated him to focus on near objects better and in all dimensions. The strug­gle for better near vision went on and this may have been a factor for evolving a simple myopic eye.

This earlier hypermetropic or emmetropic eye, suffered from various diseases and disad­vantages like presbyopia, early cataract, diabetic and hypertensive retinopathy Eales's Disease, glaucoma, pappilloedoema etc. So nature in its experiments to improve this model has produced a beautiful myopic eye with increased axial length, larger cornea, larger chamber angle, and perhaps a larger and flatter lens which may he more secure in the struggle for man with the decreased inci­dence of above diseases peculiar to the other eyes.

If so, in times to come every man will he a myopic sample rather than otherwise. Mongo­lian race is a living example. This is against the Trpn'sa Hypothesis which is a statistical analysis of only Caus-asians.




 

Top
 
 
  Search
 
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
    Access Statistics
    Email Alert *
    Add to My List *
* Registration required (free)  

 
  In this article

 Article Access Statistics
    Viewed1891    
    Printed52    
    Emailed1    
    PDF Downloaded0    
    Comments [Add]    

Recommend this journal