(c) Lighting When performing MEM retinoscopy, it is important to use normal room illumination. Accommodation is affected by illumination (e.g., dark focus), and dim illumination will alter the accommodative response. Accommodation should therefore be tested under illumination that the patient habitually uses.

Examination of eye movements involves three distinct steps: assessment of stability of fixation, saccadic function, and pursuit function (Table 1.7). Ocular motor disorders can reflect serious underlying central nervous system disease or functional or developmental problems. It is always important to consider the possibility that abnormalities in fixation stability, saccades, and pursuits may require a neurologic consultation. This is discussed in detail in Chapter 13 (Table 1.8).

The main reason for clinically assessing eye movement function is that reading consists of a series of saccades and fixations. Research has demonstrated that poor readers read more slowly and exhibit smaller and more numerous fixations and regressions. Although more research is necessary to firmly establish the causal relationship between eye movements and reading, the fact that poor readers do behave differently has prompted a great deal of interest in assessing these skills (Chapter 13).

This test evaluates the ability of the patient to maintain steady fixation on a fixation object. The most important issue to keep in mind is that assessment of fixation is often overlooked in a routine examination. Asking the patient to fixate on a target during the initial external evaluation or during cover testing is sufficient to evaluate fixation status. A variety of disorders of fixation can occur and may represent organic or functional anomalies (Table 1.9).

All patients, except the very young, anxious, hyperactive, or inattentive, should be able to sustain precise fixation, with no observable movement of the eyes, for 10 seconds (70,71).

The purpose of saccadic testing is to assess the quality and accuracy of saccadic function.