A case of

Is Snellen Visual Acuity Adequate For The Assessment Of Blurring Of Vision?


Blurring of vision is a common complaint faced by primary care practitioners from their middle- aged patients. In acute visual loss, immediate referral is warranted in all cases to rule out sight threatening conditions such as a central retinal artery occlusion or a retinal detachment.

Unfortunately, when patients come in with a chronic or subacute blurring of vision and reasonably good Snellen visual acuity, the GP is frequently faced with the dilemma of whether the patient needs to be referred on to an ophthalmologist or not. Frequently, in older patients, the most common differential is that of an age-related cataract.

Unfortunately, a Snellen visual acuity is a measure of central visual acuity and is not adequate to assess the severity of peripheral visual loss. Peripheral visual loss may occur in ocular conditions such as glaucoma or more sinister neurological causes such as in pituitary adenomas causing a bitemporal hemianopia.

In the context of a patient presenting with chronic blurring of vision, the algorithm below is suggested:-


Snellen visual acuity with pinhole
(The pinhole helps correct for most refractive errors)

Red reflex assessment with a direct ophthalmoscope

  • This allows an assessment of the severity of the cataract
  • If the red reflex is very good, the blurring of vision cannot be attributed to the cataract

Pupil examination to rule out a relative afferent pupillary defect

Visual fields by confrontation to look for peripheral visual field loss


Of note, a direct fundoscopy may be attempted but is frequently difficult bearing in mind the possible presence of a cataract and examination through an undilated pupil.


Guide To Fundoscopy Interpretation

If attempting a direct fundoscopy, examination of the disc and retina should be done.

Optic Disc Examination

When examining the optic disc, three Cs are reviewed (Cup, Colour and Contour)

  • Cup: Abnormal cupping >0.6 is suspicious for glaucoma
  • Colour: A pale disc is abnormal
  • Contour: Disc swelling is abnormal
Retina Examination

In the examination of the retina, possible colors that may be observed are RED, BLACK and YELLOW.

Red spots usually indicate the presence of either dot, blot or flame hemorrhages (Seen in the context of diabetic and hypertensive retinopathy. A central retinal vein occlusion may also present with retinal hemorrhages but patients tend to present with acute visual loss rather than chronic).

Yellow spots may be due to drusen (Age related macular degeneration), cotton wool spots (Diabetic,hypertensive retinopathy) or hard exudates (Diabetic macular edema).

Black spots are usually indicative of old scars (Previous laser scars, retinitis pigmentosa).

To keep things simple, if any of the 3 colors are seen on the direct fundoscopy, a referral is usually warranted as it indicates that the patient has a retinal disease of some sort.

Should the examination be normal and the GP feels that the chronic blurring of vision is due to mild cataracts, patients should be advised to go to their optician to get their spectacles changed. If there is no subjective improvement with spectacles, it is strongly suggested that such patients be referred on to an ophthalmologist for further assessment.


Quick Facts On New Developments in Ophthalmology

  • Progressive myopia in children can now be slowed via the use of atropine 0.01% eye drops available in all restructured hospitals. Side effects are minimal and they are well tolerated
  • Smoking is a major risk factor for age related macular degeneration (ARMD). The many eye vitamins available off the shelf containing lutein are actually based on a formulation used in the prevention of progression of ARMD found in the AREDS study. There are two important facts to note about these vitamins:-
    1. Only patients with intermediate ARMD (Drusen >125um in size) or advanced ARMD benefit from the vitamins. Patient’s without ARMD or with early ARMD had no benefit from the vitamins
    2. Vitamin supplements that contain vitamin A(Beta- carotene) were shown to confer an increased risk of lung cancer when given to smokers
  • Aside from HbA1c reduction, the use of fenofibrate in patients with diabetic retinopathy has been shown to slow the progression of diabetic retinopathy and reduce the need for ocular treatment.
    1. In October 2013, Australia became the first country in the world to add diabetic retinopathy as an indication for fenofibrate.
  • The diagnosis of glaucoma is based upon the appearance of increased disc cupping and visual field changes on formal perimetry testing
    1. Intraocular pressure elevation is not required for diagnosis of glaucoma and therefore intraocular pressure measurement is not useful for screening
    2. Snellen visual acuity may be very good even in advanced stages of glaucoma due to preservation of central vision with loss of peripheral vision
    3. Patients should take advantage of the multiple eye screening programmes nationwide (Look for advertisements in papers, community centres etc)
    4. Acute angle closure glaucoma is best diagnosed by looking for a fixed, mid-dilated pupil in patient presenting with a red eye with possible associated headache, nausea, vomiting and blurring of vision.

Dr Yuen Yew Sen MBBS (Singapore), MMED (Singapore), FAMS Associate Consultant, NUHS Department of Ophthalmology, Retina/Uveitis Service