What you need to know
|
Blurred vision is a broad term that patients can use to describe a multitude of ophthalmic complaints and therefore requires careful questioning to guide evaluation. Blurred vision is a loss of visual clarity or acuity.
It is important to differentiate blurred vision due to refractive error (the most common reason worldwide 1 ) from other symptoms that may be incorrectly described as blurred vision, such as scotomas (visual field defects), diplopia (double vision), myodesopsia ( floaters), photopsia (flashes) and metamorphopsia (visual distortions).
This article provides some tips for taking an effective history and conducting an examination to guide appropriate investigation and subsequent referral to a specialist.
How should I evaluate the patient?
Diagnostically, much can be accomplished with a careful history and basic examination in primary care. The key elements of a history are the pattern of blurred vision, associated symptoms, and medical and ophthalmologic history.
Ask about 2, 3 • Blurred vision pattern |
Typically, sudden-onset blurred vision that is painful and unilateral raises concern for an ophthalmic emergency and warrants immediate ophthalmic referral.
In contrast, gradual onset, bilateral, painless blurred vision is more often associated with conditions such as refractive error or cataracts and may be referred with less urgency.
Stable myodesopsias may suggest posterior vitreous detachment, while a barrage of new myodesopsias, persistent flashing lights with associated "visual curtain" effects (such as the sensation of a black curtain moving down the field of vision in one eye) may indicate retinal detachment.
Note that age is also an important diagnostic consideration. For example, sudden unilateral painful vision loss in an 80-year-old patient requires exclusion of giant cell arteritis, whereas a similar presentation in a 30-year-old patient may point to the ophthalmic presentation of multiple sclerosis.
directed exam
Information gathered from a focused history will point toward a probable diagnosis (see box). A focused physical examination is the essential next step to further identify red flags and determine which patients should be referred for ophthalmologic evaluation and how urgently.
When possible, the examination should include external appearance, visual acuity, visual fields, eye movements, pupillary reactions, fluorescein staining, and direct ophthalmoscopy.
Possible causes of blurred vision 4-7 Unilateral, painful and sudden onset Unilateral, painless, sudden onset Bilateral, painless and rapid onset Unilateral or bilateral onset, painless, gradual |
> External appearance
The external appearance of the eyelid may suggest periorbital cellulitis. Features of orbital involvement include proptosis, restriction in eye movement, and features of optic nerve dysfunction, such as a relative afferent pupillary defect (RAPD) or reduced color vision, any of which warrant urgent referral or admission to hospital.
Circumferential conjunctival injection or ciliary flushing may suggest uveitis, while diffuse generalized redness is more likely to suggest conjunctivitis. Sectoral injection may target episcleritis, but if the globe is tender, then the more sight-threatening scleritis should be considered.
> Visual acuity
Visual acuity should be evaluated using a Snellen chart with the patient wearing glasses if they are for long distance. This is easy to do by simply printing a 3 m Snellen chart or even using certain mobile apps.
Having vision of 6/6 or better does not completely exclude serious pathology, patients with peripheral retinal pathology may have preserved visual acuity, but good visual acuity on examination tells you that the direct path of light through the eye is relatively unobstructed (requires a clear central cornea, lens, vitreous, and a functioning macula and optic nerve).
An often underutilized tool in primary care is the use of the pinhole with Snellen charts. The pinhole is an opaque shield with one or more small openings through which the patient attempts to read the Snellen chart. These can be purchased or made by hand by creating a hole in a piece of paper with a pin or the tip of a pen 3 .
A pinhole eliminates scattered light, so that light entering the eye is focused through the center of the lens onto the retina. If patients achieve significant improvements in visual acuity with this tool, this points to a refractive component of their visual impairment.
> Visual fields
Visual field testing outside the ophthalmology service is generally performed using the confrontation method. With the patient keeping one eye closed and staring at her nose, you can test her peripheral vision by asking her to count her fingers in each quadrant of her field of vision. Repeat the test with the other eye.
This may identify serious neurological defects such as homonymous hemianopia that would require immediate referral. More subtle peripheral vision losses, such as in early glaucoma, are usually not detected with this test.
> Diplopia, ocular motility and eye movements
Monocular diplopia ( double vision that persists with one eye closed) often suggests a problem within the eye (from cataract to refractive error).
Binocular diplopia ( double vision that disappears with one eye closed), on the other hand, suggests an eye alignment problem that, if acute, could be due to cranial nerve palsy or intracranial injury, especially if accompanied by limitations typical of eye movement.
Pain with extraocular muscle use and evidence of optic nerve dysfunction may indicate optic neuritis .
> Pupils
Testing for a relative afferent pupillary defect requires balancing a bright light from eye to eye. If the pupil of the stimulated eye dilates rather than contracts, a relative afferent pupillary defect (RAPD) is present, indicating severe underlying pathology of the optic nerve or retina 4 .
Irregular pupil sizes may also be a cause for concern if the mismatch is new: causes vary from third nerve palsy to inflammatory conditions such as uveitis that causes synechiae (the iris adheres to the lens), although the latter usually presents a red and painful eye.
> Direct ophthalmoscopy
An ophthalmoscope can be used to check for red reflex. If there is no red reflex in one eye, this may indicate serious pathology in that eye. Examination of an eye with a direct ophthalmoscope provides a magnified view of the central retina and optic disc, but a limited view of the periphery. For physicians who can visualize the fundus, it would be helpful to comment on the appearance of the optic nerve and determine whether it is inflamed.
> Fluorescein stain
When available, fluorescein staining allows you to evaluate the integrity of the cornea and will highlight damaged areas of the corneal epithelium. 4 Fluorescein is widely available in the form of drops or strips. There are minimal contraindications to this test (such as fluorescein allergy), but it will require contact lens removal.
Under fluorescein staining, any areas of corneal epithelial damage will appear bright green under cobalt blue light. Prominent staining with white corneal opacification (infiltrates) could suggest a corneal ulcer, which will require urgent referral.
Other tests within primary care
After the directed history and physical examination, an ophthalmologist will perform additional evaluation (see box). Some testing may be indicated at the primary care level if the history and physical examination findings are consistent with a new systemic illness or worsening of an existing one.
The following blood tests may be considered:
• HbA1c in patients with suspected diabetic retinopathy 9 11 (typically patients with known diabetes).
• Inflammatory markers such as erythrocyte sedimentation rate, plasma viscosity or C-reactive protein may be useful in patients with suspected giant cell arteritis with ocular involvement or other inflammatory etiologies in addition to urgent referral to ophthalmology.
• Blood pressure should be measured in all new cases of blurred vision.
Referral criteria 4 5 7 8 Urgent same-day referral or urgent discussion with ophthalmology • All patients with ocular trauma. Refer to an ophthalmologist (the patient should be seen within a few days) or consult the ophthalmology service if there is any doubt. • New myodesopsias with persistent flashes. Routine referral to ophthalmology • Gradual onset blurred vision that is completely corrected with orifice occluder without any associated visual symptoms |
Local referral protocols may differ, and it is important to be aware of regional guidelines and service availability. It may not be safe for patients with significant vision loss to drive, and patients with blurred vision should be counseled accordingly.
Education in practice
• Ask about risk factors for diabetes or hypertension when a patient has gradual onset blurred vision?
• Think about the last time you examined a patient’s visual fields. Were you clear with his instructions or was there a learning curve for the patient? How could you modify your language to ensure a more accurate and efficient test?
