Year : 1981 | Volume
: 29 | Issue : 3 | Page : 261--262
Ocular manifestations of high altitude
Army Hospital Delhi Cant, India
R C Sharma
Army Hospital Delhi Cant
|How to cite this article:
Sharma R C. Ocular manifestations of high altitude.Indian J Ophthalmol 1981;29:261-262
|How to cite this URL:
Sharma R C. Ocular manifestations of high altitude. Indian J Ophthalmol [serial online] 1981 [cited 2024 Feb 28 ];29:261-262
Available from: https://journals.lww.com/ijo/pages/default.aspx/text.asp?1981/29/3/261/30898
Ocular manifestations of high altitude is a topic not very common but very important more so for the Armed Forces. Obviously this aspect has not been studied in detail in the pastas this was confined to a couple of mountaineers or people who were interested in high accent by balloons. This problem has become of great importance in view of our extensive borders which have to be guarded the year round. The ocular changes are all related to changes in atmosphere pressure.
Changes in atmosphere pressure may pro�duce symptoms among which ocular effects may be prominent in 3 ways :�
Raising of the atmospheric pressure.Lowering of the Barometric pressure.Sudden relative diminution of atmospheric pressure.
Our Ophthalmic problems are mainly due to anoxia at low Barometric pressure.
The essential defect in the atmosphere at high altitude is the lack of 0 2 which at all levels retains its relative pressure of 1 /5 of the total.
At the same time in the alveolar air, the water vapour and CO 2 derived from or within the body maintain their pressure independently of that of outside air, so that as barometric pressure diminishes alveolar oxygen tension decreases disproportionately until at 50,000 feet. When pressure of the inspired air 86 mm of Hg, alveoli of the lungs are for all practica�ble purposes filled with moisture.
General Symptoms of anoxia depend on the rapidity with which a low barometric pressure is reached as well as on extraneous factors as cold, exertion and so on. The first effects are seen on functioning of brain�judgement is impaired, mental processes are slowed, muscle coordination fails, unconcious�ness supervenes particularly if muscle exercise consumes the depleted stores of O 2 available.
The great vulnerability of nervous tissue to anoxia may be explained by the unusually high oxygen consumption of the brain i.e. 8% of total O 2 consumption of the body (13 ml 02 for 100 gm wet brain weight per minute).
OCULAR MANIFESTATIONS OF HIGH ALTITUDE (ANOXIA)
I. Vascular changes are the most important and permanent.
(a) Vascular Engorgement-is a perma�nent feature. It becomes apparent at 12000 feet and reaches at its maximum at 18000 feet. The A/V ratio becomes 1 : 2. 4. This is a physiological adaptation to anoxia.
(b) Vascular Tortuosity-in addition to vascular engorgement, tortuosity of vessels is also seen.
(c) Haemorrhages-superficial striate and flame shaped haemorrhages are found any�where in the fundus but surprisingly macula is spared, hence called symptomless haemorr�hages. These are mainly due to hypoxia which stimulates massive retinal vasodilation making retinal vessels vulnerable to sudden, severe rise in intravascular hydrostatic press�ure. Increased blood viscosity specially is acclamatised person and vascular obstruction are other contributory factors.
II. Intra Ocular Pressure-There have been conflicting reports but in our series, it has shown that 1.0. pressure falls (117 subjects were studied (234 Eyes). In 60% it was below normal and normal in 40% of cases. (taken 18 mm of Hg Schiotz as normal).
I.O.P. decreases with exercise, particularly increasing the chance of intra-ocular bleeding,
III. Cataract seen experimentally in mice exposed to altitudes of 30,000 feet or more Opacities are vacuolar in type and lie in superficial layers of cortex and these are rapi�dly reversible. These are associated with a rise in lactic acid content in aqueous humour to 3-4 times (normal 20-28 mg%). No such changes seen in men.
IV. Pupil dilates in acute anoxia. No changes were seen in our series.
V. Motor Functions are rapidly impaired. Lack of muscular coordination which become evident in highly complex ocular movement before it is conspicious in muscles of limbs. Tendency is towards esophoria. Esotropia with Diplopia is common above 1200 feet.
Functional changes in vision are more common and important than organic changes as their practical significance is considerable. Most of the symptoms are due to failure in cerebration and their incidence and degree vary in different
Visual Acuity-is decreased by 6% at 12000 feet and by 12% above 12000 feet. Vision becomes normal within 10 minu�tes with an adequate oxygen supply.Light Sense-Rate and extent of dark�adaptation is impaired. It becomes evident at 7,500 feet, significant at 11,000 feet and constant at 15,000 feet. Restoration occurs after inhalation of oxygen.Field of Vision-both in form and colour show peripheral construction. This deficiency is compensated for sometime if attention is stimulated thus demon�strating that it is of central origin. In our series we have 3 cases who showed permanent loss of peripheral fields with no other positive ocular findings.Colour Vision-is disoriented apart from constriction of colour fields. Above 10,000-12,000 feet colour appears less saturated.After Images-Latent period for develop�ment of after images is increased-even�tually abolished.Higher Visual Functions
- Sterioscopic vision is depressed and may be abolished.
- Critical frequency of flicker is lowered.
- Visual illusions are prone to develop. These higher function can be counter�acted for a period with stimulants (Benzedrine) but visual function returns rapidly when tension of oxygen is restored.