The leader of the research team, Muhammad Waseem, said the corrected visual acuity and colour vision was checked by one optometrist. These candidates were tested on Ishihara Pseudoisochromatic plates (38 plate edition 2009). – File Photo

KARACHI, March 9: About seven per cent of the men seeking recruitment in various branches of the armed forces and civil aviation were found colour blind, reveals a recent study. On the other hand, aspirants for admission to professional education institutions, including engineering and medical universities, having undergone medical fitness tests in recent years were also found having colour vision defects.

They said in the commonest form of colour blindness people could not distinguish red from green. More than 95 per cent of all variations in human colour vision involved the red and green receptors in men's eyes.

At a recent medical ophthalmology conference, a group of doctors from the PNS Shifa Hospital made a presentation on colour vision anomalies in candidates seen at the naval hospital to detect frequency of colour vision anomalies.According to the study, involving 500 candidates from candidates seeking enrolment in the Pakistan Navy, Air Force, Army Aviation and Civil Aviation, and other walks of life, conducted during between July 15, 2010 and Jan 10, 2011, 35 had colour vision defects. According to services personnel, such candidates faced disqualification.

The leader of the research team, Muhammad Waseem, said the corrected visual acuity and colour vision was checked by one optometrist. These candidates were tested on Ishihara Pseudoisochromatic plates (38 plate edition 2009).

A specially designed form was used for recording the particulars, consent and endorsement of findings. Data so collected was subjected to SSP 16 version for analysis of frequency of colour vision anomalies.

Since the available study data showed that a significantly large segment of the candidates had colour vision defects, there was a need to do more work in this respect, the ophthalmic said, adding that the study was being extended to another 500 candidates.

When contacted, the registrar of the NED University of Engineering and Technology, Javed Aziz Khan, said this year around 2,000 candidates were tested for medical fitness, of whom 80 were found colour blind.

According to the university's admission criteria, colour blindness disqualifies applicants for the disciplines of mechanical, electrical, computer and information system, textile, industrial and manufacturing, electronics and telecommunication engineering, he said, adding that such candidates might be considered for other disciplines.

Prof Idrees Adhi, head of the ophthalmology department of the Dow University of Health Sciences, said colour blindness was one of the common genetic disorders observed in all human populations.

Though the deficiency can be caused by eye diseases or normal aging or is acquired from the environment, a majority of such patients inherited it due to a gene attached to the X chromosome, he said, adding that men having only one X-chromosome were far more susceptible to colour vision abnormalities than women, who have two.According to him, an affected man passes the colour-deficiency gene to all his daughters, who then become unaffected carriers, while his sons get his Y chromosome and have normal colour vision. Each son of carrier women has a 50-50 chance of getting the gene from his mother.

He said a friend of his was also colour blind, who managed to follow traffic signals just watching what other drivers did on roads.

He said colour blind people always knew the position of the colors on the traffic light -- red on top, yellow in the centre, or green on the bottom, but it could not be good for them when they go to a place where traffic lights were put horizontal or when they came across with a caution light -- only one light. In the light of his personal experience as a physician, he suggested colour blindness test for medical workers, particularly those working as technicians in laboratories or handling vaccines and injections.

He also confirmed that in routine medical tests during a period of three years a number of applicants for MBBS programme at DHUS had been found colour blind.

A senior official at a public-sector university said his son was normal like his other wards and he came to know about his colour problem only when he appeared for selection in the PAF and after a test was declared colour blind. However, he had no problem in school and during the years had learnt to live with the vision deficiency, he added.

According to researchers, the human eye relies on its 6-7 million cone and 100-130 million rod cells to produce normal vision. The cones -- blue, green and red -- are located in the centre of the retina and are responsible for colour vision, light adaptation, and the detail. The rods are located in the periphery of the retina and are responsible for night vision, brightness perception, and distinguishing shapes.

They reported that the red-green deficiency was the most common colour vision abnormality. The mildest form of this deficiency are protanomaly, where blue-green and red-purple are perceived as an indistinct grayish shade, and deuteranomaly, where green and red-purple are perceived as an indistinct grayish shade.

Dr Alyscia Cheema of the Jinnah Postgraduate Medical Centre said there was no formal research or data collection on colour vision problems, but she could say that in Pakistan, too, the rate of such cases would come to around 7pc to 8pc, mostly involving males. “We come across such patients with minor deficiencies from time to time while reporting on patients with severe deficiency at the JPMC,” she said.

According to Prof Adhi, people whose colour vision deficiencies are mildly affected can easily perceive some colours and might pass some of the tests, but the persons who had a significant and potentially hazardous colour vision would fail to clear a relevant test.