Visual Acuity Testing

Contrast Sensitivity Testing

Contrast sensitivity testing is important for the assessment of both sensory disease and media opacities. With media opacities, such as cataracts, a general depression occurs in contrast sensitivity at all points, with a slightly greater depression at lower contrasts.

Glare Testing

Glare testing is useful in the assessment of media opacities, such as cataracts. The effects are negligible in sensory disorders, except for a few macular disorders, such as cystoid macular edema (CME), in which intraocular light scatter occurs in the superficial layers of the retina. Even with this disorder, the changes in glare disability are minimal. Glare testing can be very sensitive and specific to media opacities, but more importantly, it gives visual acuity values or equivalents that relate to a person’s vision in daylight, as opposed to vision in a testing room with high-contrast letters.

Visual Fields

The integrity of visual fields is particularly important in patients with sensory disorders, such as glaucoma and optic neuropathies, and patients who have suffered strokes that have affected the visual pathways. Unfortunately, these disorders also are common in the age group that suffers from cataracts and may go undetected until after the cataract surgery. Additionally, visual field defects that result from strokes may change the risk–benefit ratio for cataract surgery, particularly if the stroke occurred recently.

Color Vision

Color vision is specifically important in sensory disease, such as retinopathies and optic neuropathies, which often show characteristic color vision changes that help make the differential diagnosis and monitor the effect of therapy. In patients who have ocular media disorders, such as cataracts, the changes in color vision can usually be correlated with the color of the cataract. For example, a patient who has a brunescent (yellow-brown) cataract has significant deficiencies in the blue end of the visual spectrum (shorter wavelengths). When color deficiencies do not correlate, sensory disorders should be suspected. Although color vision testing is very sensitive in some disorders, such as central serous maculopathy and CME, by “bleaching” or reducing the apparent brightness, other parameters, such as visual acuity, visual field, and contrast sensitivity, are also affected, which makes routine color testing unnecessary.

Standardized Visual Acuity Testing

Standardized visual acuity tests measure the ability of a patient to recognize standardized optotypes (usually Snellen acuity letters) at a specified visual angle, illumination, and contrast. Visual acuity can be recorded in various notations, in which normal vision would be Snellen units 20/20 or 6/6, decimal notation 1.0, or logarithm of minimum angle of resolution (LogMAR) 0.0.

Potential Retinal Acuity Testing

A special type of acuity test used in cataract patients is the assessment of potential retinal acuity. This test is essential for patients who have pigment mottling in the macula and reduced vision, particularly in the presence of a cataract or other optical aberrations of the eye. In the cataract age group, the incidence of macular degeneration is at least 10% and may exceed 15%, depending on the age of the patient. It is important that both the surgeon and the patient have a realistic expectation of the quality of postoperative vision, which helps both parties to accurately assess the risk–benefit ratio. Removal of a significant cataract always should be considered, even in the presence of an abnormal macula or if the predicted acuity is low.

Best-Corrected Visual Acuity

The term best-corrected visual acuity implies that the patient’s eye has been optically corrected to achieve the best visual acuity. In most cases, this value is obtained with best spectacle refraction. In cases of irregular corneal astigmatism, the BCVA may be attained with a rigid contact lens, not with spectacles. In recent studies with known preoperative pathology excluded (best case analyses), between 97% and 98% of the patients who had received cataract surgery achieved BCVA equal to or better than 20/40 (6/12; 0.5). A suggested standard was to achieve a final BCVA of 0.5 or better in 97% of all cataract extractions in eyes with no ocular comorbidity. The corresponding number for all routine patients with cataract, including those with ocular comorbidity, was 94% in a recent report ( Table 5.18.1 ).

Uncorrected Visual Acuity

The term uncorrected visual acuity (UCVA) refers to the patient’s vision in standard conditions with no extraocular optical correction. Unlike BCVA, several additional factors (e.g., pupil size, degree of refractive error, and amount of regular astigmatism) also influence the measured visual acuity. UCVA is most useful in the evaluation of specialty lenses, such as multifocal and toric intraocular lenses (IOLs). The goal when using these lenses is to reduce or eliminate the patient’s dependence on glasses and to achieve good uncorrected distance visual acuity (UCDA) and near visual acuity. To achieve target refraction is crucial when using multifocal IOLs. Unfortunately, multifocal IOLs have a tendency to give more glare and halo compared with monofocal IOLs. This applies to most types of IOLs with more than one focus, and to construct the optimal IOL for both near and distant vision is an area of active research. UCVA can be used as a quality characteristic of the surgical procedure, especially on the day after surgery. For this purpose, however, it is relevant to use the target refraction if, for instance, postoperative myopia is planned.

Target Refraction Prediction Error

Another factor in the determination of UCVA is the ability to achieve the target postoperative refraction. Most surgeons target the majority of their patients for postoperative refractions in the range of 0.0 to −0.50 D. With modern biometry equipment, newer IOL formulas, personalization of lens constants, and improvements in surgical technique, at least 90% of patients should have sphero-equivalent refraction within ±1.00 D of the intended target. In a recent study on routine cataract surgery, about 90% of cataract extractions resulted in a final refraction within ±1.0 D of the intended target refraction (see Table 5.18.1 ). A suggested standard was a biometry error with a correct sign centered on 0 D and with 87% or more of the values within ±1 D of error.

Surgically induced astigmatism (SIA) may be intentional or not intentional. Small-incision cataract surgery results in less SIA than did earlier, larger-incision surgical techniques. The magnitude of SIA may be less than 0.5 D on average, depending on incision site and incision size. The best outcome of cataract surgery with respect to astigmatism is usually to achieve as low a postoperative astigmatism as possible. SIA can be used to achieve this result by varying the placement of the incision. SIA, thereby, can counteract preoperative astigmatism and result in reduced postoperative astigmatism.

Contrast Sensitivity

Following cataract surgery, in the absence of other ocular disease, the contrast sensitivity returns to normal. Binocular contrast sensitivity may not be normalized until second eye surgery has been performed, given the occurrence of cataract in both eyes.

Glare

Studies have documented that the correlation of most of the instruments used for glare testing and outdoor vision testing show a dramatic improvement after cataract surgery.

Visual Fields

The visual field returns to normal after cataract surgery in the absence of ocular comorbidity.

Color Vision

After cataract surgery in patients who have blue-color deficiencies caused by the cataract, the return to normal color vision is perceived as sensational by some patients but is not even noticed by others. Color vision returns to normal in the absence of other ocular disease.