Open Angle Glaucoma

In Singapore, the overall prevalence of glaucoma is 4%- meaning that in your lifetime, you have a 4% chance of developing glaucoma. Not a big number- the odds are still in your favour, but it is still a condition worth knowing about.

Open angle glaucoma accounts for nearly half of glaucoma in Singapore- 1.7% of the population have or will have this disease. That figure does not sound intimidating. What is worrisome is that this disease does not have many symptoms, and many patients are diagnosed late for this reason.

In open angle glaucoma, the optic nerve at the back of the eye undergoes progressive damage. This is most often (but not always!) due to high eyeball pressure. Contrary to popular belief, this rarely causes pain or discomfort to the eye, and the patient is often unaware that he has glaucoma.

The result of optic nerve damage is visual field loss- reduction in the patient’s peripheral vision. Peripheral vision is important in daily life- it allows us to safely cross roads or drive, for example, but early peripheral vision loss is usually not noticeable. A loss of central vision is noticed by patients immediately, but loss of peripheral vision is much more subtle and can progress to severe loss before it is perceived by the patient.

As a result, open angle glaucoma is often diagnosed late, when significant peripheral field loss has occurred. Occasionally patients present when only tunnel vision remains, or worse, when the peripheral field is completely lost and the disease starts to affect central vision.

How is open angle glaucoma diagnosed? When patients present to an Ophthalmologist, a detailed history and physical examination is performed. Intraocular pressure is measured- usually raised beyond 21mmHg in the case of open angle glaucoma. Signs that point to the disease- a characteristic weak, thinned-out appearance of the optic nerve, would make one suspicious of the disease. The disease is often confirmed on further testing, where both structure and function of the nerve is tested. High resolution Optical Coherence Tomography (OCT) scans of the optic disc and the surrounding nerve fibre layer can determine if there is any thinning of the nerve due to glaucoma, and Humphrey Visual Field (HVF) testing can map out areas of visual field loss.

 

High resolution OCT image showing significant nerve fibre layer thinning. The red areas in all the circular plots are abnormal.

How is open angle glaucoma treated? Several eyedrop medications exist that can be instilled to lower intraocular pressure and reduce the progression of nerve damage. If eyedrops are insufficient to treat the disease, laser procedures and surgery can also be done to manage the disease.

If you are over the age of 40, or have a family member who has glaucoma, it is a good idea to go for a comprehensive eye screening to ensure that you do not have this problem.

Cataract Surgery- when I was wrong

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I have been a cataract surgeon for over a decade now, and with that experience, I am usually fairly accurate in my clinical assessment of how well my patient will fare after surgery. Occasionally I am surprised myself by the outcomes, just like I was on a case I operated on last week.

Mdm C is not your typical patient. She presented to me with poor vision in the right eye, and on examination she did indeed have a cataract in that eye. However, she was also markedly short sighted in that eye, and had been so since childhood. Her spectacle degree in that eye was 750 degrees, with astigmatism of 225 degrees. Her vision was perfect in the left eye without glasses. Due to the large imbalance between spectacle degrees of both eyes, she had lived her life without glasses and relied heavily on the left eye, and had lived with poor vision in the right eye for decades.

In this case, there is a high chance that she has developed a lazy eye in the right eye. In childhood, vision must be good in both eyes in order for pathways between the eye and brain to develop normally. If vision is better in one eye, the poorer eye will become “lazy” and the pathways to the brain will not develop normally. This is a condition known as amblyopia. Pathways mature when a child reaches the age of 8, and beyond that age, the vision in the lazy eye cannot be improved.

In Mdm C’s case, I felt that the likelihood was high that she had amblyopia in the right eye, as she had been highly short sighted in that eye all her life. As a result, even with cataract surgery, I felt her vision would not be as good as her left eye.

I discussed this at length with her and her son, explaining to them the benefits and risks of cataract surgery, as well as my concerns that her vision would not be perfect in the right eye even after surgery. However, as her vision in the right eye was very poor, she decided to proceed with surgery despite the guarded prognosis. Her vision was 6/120- she was only able to see the biggest letter on the chart.

Surgery proceeded uneventfully. I removed the cataract and implanted a toric intraocular lens in the right eye, which corrects for both short sightedness as well as astigmatism.

She returned for review on the first postoperative day. When I opened her chart, I thought I had the wrong patient. Her vision in the right eye was 6/6- perfect vision!

Mdm C was ecstatic. She had not seen well in the right eye for decades as it had always been highly short sighted, and had never worn glasses or contact lenses in that eye. For the first time in her life, she had good vision in both eyes.

I had been wrong about my assessment that she had a right lazy eye- and I had never been so happy to have made a misdiagnosis.

I am always delighted when my patients achieve good outcomes, there is nothing more satisfying to me than restoring vision to my patients. When outcomes exceed expectations, I can only be humble and grateful, to God for whom nothing is impossible, and to my patients, for putting their faith in me, and giving me the privilege of being their cataract surgeon.