A woman of Japanese origin has cup-to-disc ratios of 0.6 in each eye with pale (pallor) neural retinal rims. At the examination two years previously another optometrist noted her cup-to-disc ratios in each eye as 0.5 in each eye. Her intraocular pressures are 18 mmHg in each eye and were 17 mmHg in each eye at the previous examination. What is going on?
The key factors here are Japanese origin, high cup-to-disc ratios in each eye, an increase in the cup-to-disc ratio, pale neural retinal rims in each eye and intraocular pressure in the normal range in each eye.
This sounds very much like glaucoma other than the intraocular pressures that are in the normal range. The increase in the cup-to-disc ratio may simply be intraobserver variation were one optometrist’s cup-to-disc ratio estimation is higher or lower than another’s. Measurement of the cup-to-disc ratio is usually a subjective one made using some form of ophthalmoscopy. It is an estimation and estimations vary between people. What is highly suspicious in this case is the novel finding of neural retinal rim pallor.
It sounds like normal-tension glaucoma, which is also known as low-tension or normal-pressure glaucoma. It is a form of glaucoma where the optic nerve is damaged when the intraocular pressure remains in the normal range. The cause is not known but for some reason, the optic nerve is susceptible to damage even in an environment of normal intraocular pressure
- People are at a higher risk for this form of glaucoma if they have:
- A family history of normal-tension glaucoma
- Japanese ancestry
- A history of systemic heart disease such as irregular heart rhythm.
For some reason, the optic nerve is susceptible to damage from even the normal amount of eye pressure. This patient needs to undergo visual field testing which is likely to show glaucomatous visual field defects. Referral to an ophthalmologist specialising in glaucoma is required. If visual field defects are not found or visual field analysis equipment is not present in the practice the patient should still be referred because of the suspicious changes to the optic discs.