The optical property of this opacification is diffusive. The opacification of the lens capsule is caused by a layer of granulated calcium deposition. This parametric modeling included variables such as diffusiveness of the capsular bag, capsulorhexis size, and pupillary diameter. The causal relationship between optical features and photic structures was examined by focusing on individual components (e.g., surfaces, edges, or haptics) while blocking all other components using ray-tracing technology. The final image on the detector consisted of a primary image formed through the optic, multiple reflections formed by surfaces, edges and haptics, and direct light that missed the IOL body totally. However, the logarithmic scale was used to examine the optical details of the photics. Like the retina that responds to illumination, the detector typically detects the light intensity on a linear scale. The virtual detector used in the simulation was shaped as part of a sphere with a 6 mm aperture contoured as the retinal shape and centered on the primary image location formed by temporal incident light 75° off-axis from optical infinity. Virtual Zemax detectors are used in the simulation to detect distribution of light intensity at desired locations on the retina surface.

The detector was part of a sphere with a 6 mm aperture contoured as the retinal shape and centered on the primary image formed by temporal incident light 75° off-axis from optical infinity. Schematic drawing of the NSC modeling in Zemax to show the major optical components and the light passages after reflected and refracted by the components. Findings from the optical modeling support the hypothesis originally proposed by Masket and Fram 8 that the negative dysphotopsia may be considered a complication of anterior capsulorrhexis with in-the-bag IOL implantation. In the present investigation, we attempted to establish an optical model to simulate the photic phenomenon experienced by the human eye on the peripheral retina. Optical modeling or simulation plays a central role in deriving new experimental knowledge to better understand the precise biological system and optical design of the eye. 2, 3, 4, 7 Other proposed causes of negative dysphotopsia include individual predisposition, optical interference of light, and complex interactions between the IOL optics and the optics of the eye. Many experts believe that the edge of the IOL causes the patient to perceive a temporal shadow and have noted this with a wide variety of IOL designs. 3, 7 Although this visual phenomenon is tolerable by most patients and its magnitude usually lessens or disappears over time, it becomes a bothersome symptom for some patients, and may even result in secondary surgery in the worst cases. However, negative dysphotopsia has been described as the most troublesome complaint after uneventful IOL implantation surgery. 2, 3, 4 The physiological mechanisms leading to negative dysphotopsia remain an enigma, and its causative factors have been elusive. Negative dysphotopsia is a relatively common complication and poorly understood photic phenomenon that may follow cataract surgery with in-the-bag implantation of a posterior chamber IOL. This study further determined that 6 of the 14 patients had positive dysphotopsia, 6 negative dysphotopsia, and 2 combined features. Conversely, DavisonĢ showed that only 0.2% (14 of 6,668 cases) of patients reported dysphotopsia after cataract extraction with IOL implantation. In another study, BournasĦ demonstrated that 117 (19.5%) of the 600 patients reported dysphotopsia during the first follow-up visit. Testerġ reported that 49% of the 302 patients had some type of dysphotopsia after cataract extraction with implantation of IOL. In a study by Shambu and co-workers 5 involving 111 patients who underwent uncomplicated cataract surgery, the reported overall incidence of dysphotopsia was 77.7%. The prevalence of dysphotopsia after cataract surgery and IOL implantation is unknown and its incidence varies widely.

Conversely, negative dysphotopsia is characterized by the perception of dark shadows of crescent shape, which can be arc-shaped, usually in the temporal field of vision. Positive dysphotopsia is perceived by patients as brightness, halos, or streaks, and rays emanating from a central point source of light, sometimes with a diffuse hazy glare. 1 The photic phenomena can occur either as a positive or negative dysphotopsia. The term dysphotopsia was originally introduced by Tester and co-workers in 2000. The manifestations of the photic phenomena include transient glare, streaks, arcs, halos, and edge effects and have been collectively described as dysphotopsia. Optical side effects are well-documented associated symptoms of visually undesired photic phenomena following an intraocular lens (IOL) implantation surgery.

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