**1. Introduction**

Cataract surgery has been one of the great ophthalmological contributions to the worldwide prevention and treatment of blindness.

The first cataract surgery was performed by an Indian surgeon, Sushruta, in the fifth century BC. [1–3]. Over time, improvements in cataract surgery led to many advances, such as the replacement of the opaque crystalline lens with an intraocular lens (IOL). The first IOL implant was performed by Sir Harold Ridley on November 29, 1949, at St. Thomas Hospital, London [4, 5]. Thanks to the contributions of many scientists and surgeons, techniques improved as well as IOL design. However, with the use of new technologies, complications or unwanted side effects may also arise. Dysphotopsia secondary to IOL [6, 7], is the reason for this chapter.

#### **2. Pseudophakic dysphotopsia**

Dysphotopsias are visual phenomena caused by light in phakic and pseudophakic patients. The term was introduced by Tester et al. [6] in the year 2000, and included all entoptic phenomena triggered by light (glare, halos, and dark arc). These phenomena frequently bother the patient, producing a certain degree of dissatisfaction, even in circumstances where there is good visual acuity (20/20 or better).

Dysphotopsia in phakic patients may improve with correction of the refractive error [8], special lenses [9], sunglasses [10], lenses with filters [11] and other techniques. In patients with significant cataracts, surgery is the option [6]. Before the advent of IOLs, aphakic patients (without IOL) who were placed in contact lenses reported glare phenomena [11]. The first report was by Koetting and Von Gunten in 1969 [12]. Subsequently, with the emergence of IOLs, patients with pseudophakia began to experience visual phenomena more emphatically than they did before surgery [13]. However, the benefit of improvement in visual acuity generally compensated for problems with dysphotopsia. A number of clinicians and researchers have tried to determine the causes of dysphotopsia [13].

Initial reports considered causes including the pupil, the intraocular lens, and the posterior capsule. This is reflected in one of the initial publications by Doden in 1984 [14]. This author studied the pupillary changes observed in 2500 eyes operated on cataract by extra capsular technique and phacoemulsification. He associated glare with the optical irregularity caused by the pseudophakia "per-se" or the opacities affecting the posterior capsule. Subsequently, sophisticated techniques were employed, refining the studies and reducing the number of causative factors to IOL as well as opacity of the posterior capsule [1, 12, 13, 15].

Between 1994 and 1995, the 6 mm and 5.5 mm acrylic IOL were introduced, which allowed patients to have calm eyes in the postoperative period, that is, with less chance of developing anterior uveitis and cystoid macular edema. They also found that these lenses caused less fibrosis and opacities of the posterior capsule, with lower capsular contraction, reduction of optical precipitates, and good optical centering [16]. Based on this, it was postulated that the square edge of the intraocular lens was the primary reason for the above findings [15, 17, 18]. In the laboratory, Nishi [15] confirmed that the edge of the IOL acted as a barrier to cell migration within the posterior capsule independent of the material. Unfortunately, the edge also caused a new undesirable visual phenomenon resulting from internal reflection due to the angle of incidence of oblique light. This was often referred to by the patient as a dark shadow in a half moon shape or an arc in the temporal field. The effect was more annoying than previously reported, proving even difficult to predict which patient could develop this symptomatology [15, 17, 19, 20].

Pseudophakic dysphotopsia was presented for the first time by Olson, MD, at the XVIth Congress of the European Society of Cataract & Refractive Surgeons, in Nice, France, on September 1998 [7]. Initially, it was thought that this visual phenomenon was transitory. Overtime the visual effect persisted as a souce of visual compliants, resulting in a number of procedures to attempt to reduce or solve the problem. In 2000, Davidson [7] divided these dysphotopsia phenomena according to the symptoms into positive and negative.
