Irregular corneal astigmatism is often first identified as an irregular reflex during retinoscopy. Often patients have seen many eye doctors, and have been given a variety of contact lens or eyeglasses prescriptions. Visual field testing tends to be normal or show an overall slight depression. Patients with this diagnosis typically complain of blurred rather than dim vision. This condition may result from contact lens wear, ocular surgery, or intrinsic disease of the cornea such as keratoconus ( Figure 6–2). Irregular corneal astigmatism may be a cause of unexplained decreased visual acuity or monocular diplopia. Ointment at night, punctal plugs, Restasis, and other measures may be helpful if indicated. Patients with intermittent, variable blur and ocular pain/foreign body sensation or other signs of ocular surface disease may benefit from a trial of artificial tears (at least four times a day for several weeks) before (or concurrent with) further neuro-ophthalmic investigation. Tear film stability is also weakened by debris in the tear film, such as the products of chronic blepharitis.Įvidence of ocular surface disease at the slitlamp includes punctuate staining (with topical fluorescein or rose bengal) of the exposed area of the cornea, rapid tear breakup time (observing the fluorescein-stained tear film fall apart prematurely after a blink), deficient tear meniscus (normal adherence of tears along the lower lid margin is minimal or absent), and injection of the conjunctiva in the exposed area between the lids. (Patients often question why artificial tears are recommended when their complaint is “too much tearing”). Tear film dysfunction can result in overproduction of the aqueous component, which fails to adhere to the eye and simply accumulates until it falls over the lower eyelid. Deficiencies in any of the three layers can cause the tear film to break up too soon or evaporate too quickly. This arrangement allows the tear film to distribute evenly over the ocular surface, pulled up as a sheet with each blink. The tear film is complex, consisting of three distinct layers: (1) an inner mucous layer that adheres to the ocular surface, (2) an aqueous layer in the middle that is the thickest layer, (3) an outer lipid layer that retards evaporation. Tear film dysfunction is a very frequent cause of blurred vision, eye pain, red eyes, and tearing. In addition to providing nutrients to the cornea, the tear film provides a smooth surface over the corneal curvature to optimize the optics of the eye. The importance of the tear film in maintaining clear vision is not always appreciated by physicians. Meibomian gland dysfunction and blepharitis can cause destabilization of the tear film and further exacerbate dry eye syndrome ( Box 6–1). Tear film disorders resulting in inadequate tear coverage can actually cause excessive tearing, but this reflex tearing consists of watery tears that fail to adhere to the ocular surface. A foreign body sensation and conjunctival injection are often present, but may not be prominent. The patient’s visual acuity may vary widely between examinations. Sometimes the blurred vision clears momentarily with a blink. Patients frequently describe blurring that begins 2 to 3 minutes into a task requiring concentration, such as reading or driving. Dry eye syndrome is very common in women older than 40 years, but is also associated with collagen vascular disease (Sjögren syndrome and many others), medications, systemic disorders (such as sarcoidosis), and neurological conditions (eg, progressive supranuclear palsy, Parkinson disease, facial nerve palsies). Tear film disorders, such as dry eye syndrome, commonly cause transient visual blurring that may range in duration from seconds to hours in one or both eyes (see Table 1–3).
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