Magnification Characteristic of a ؉90-Diopter Double-Aspheric Fundus Examination Lens

PURPOSE. To investigate the magnification characteristic of the ϩ90-D double-aspheric fundus examination lens for biomicroscopic measurement of the optic disc. METHODS. A calibrated Gullstrand-type model eye adjusted for axial ametropia between Ϫ12.5 and ϩ12.6 D was used to measure the change in magnification of the system with refractive error and variation in fundus lens position. A correction factor p (in degrees per millimeter) at different axial ametropias was also calculated. RESULTS. The total change in magnification of the system from myopia to hyperopia was Ϫ15.1% to ϩ13.7%. When the fundus lens position was altered with respect to the model eye by Ϯ2 mm under myopic conditions, the change in magnification of the system was Ϫ4.8% to ϩ8.1%. In the hyperopic condition the change was Ϫ4.8% to ϩ6.0%. The fundus lens exhibited a linear relationship between p and the degree of ametropia of the model eye and a constant relationship between p and ametropia of Ϫ5 to ϩ5 D. CONCLUSIONS. Axial ametropia has a significant effect on biomicroscopic measurement of the optic disc with the ϩ90-D lens. Therefore, a correction factor (p) was calculated that can be used in calculations for determining true optic disc size. These findings may be important for improving clinical disc biometry. (Invest Ophthalmol Vis Sci. 2002;43:1817-1819 D etermining the actual size of the optic disc is possible by histopathologic study, magnification-corrected photogrammetry, scanning laser ophthalmoscopy, or use of the interference fringe scale. 1-4 However, the aforementioned methods are not applicable in a routine clinical setting. Measurement of the optic nerve head is usually performed at the slit lamp biomicroscope using an auxiliary lens to overcome the high focal convergence of the examined eye. In this study, we investigated the magnification characteristic of a ϩ90-D fundus examination lens over a wide range of ametropia in the center of the image field. MATERIALS AND METHODS A commercially available ϩ90-D double-aspheric fundus lens (Volk Opticals, Mentor, OH) and a calibrated slit lamp biomicroscope with adjustable beam length (model 900; Haag-Streit, Bern-Koeniz, Switzerland) were used for this study. It is well known that the calculation of the true size of an object in the ocular fundus depends on the knowledge of the refraction, corneal curvature, and axial length of the eye (correction factor q, in millimeters per degree) To measure the change in magnification of the system with refractive error and variation in condensing lens position, a curved scale in the form of concentric half circles was fitted with the help of an excimer laser in the center of the artificial fundus surface of a calibrated Gullstrand-type model eye. This scale has to be curved, because the optics of the slit lamp biomicroscope and fundus lens are designed for use with a curved field, so that a flat scale is only approximate to the retina in practice. An image of the scale has recently been published. The fundus object was viewed with the fundus lens as in a routine examination of the optic nerve head. The instruments were aligned perpendicularly to the model eye's cornea, and the fundus object was brought into focus by moving the biomicroscope away from the condensing lens until a sharp image of the fundus object was provided in the center of view. A narrow slit beam, with width maintained at 0.2 mm, was progressively reduced in size from 8 mm until it coincided with the diameter of the smallest half circle, which has a true size of 4 mm. The beam length was then recorded, by the second observer, from the millimeter scale at the top of the instrument. Because the slit lamp beam length is calibrated in 0.1 mm, the reading was judged to the nearest 0.05 mm. After each reading, the millimeter scale was reset to 8 mm. Measurements were taken with the vitreous depth of the model eye set at a range of ocular refractions from Ϫ12.5 to ϩ12.6 D. The pupil diameter was 8.0 mm. At each ametropia setting, three measurements were obtained. By dividing the measured length by four, we obtained the actual magnification of the fundus image at the different axial ametropia settings, and by the formula p ϭ (k/17.453)(t/s), where k is the ametropia of the eye ϩ equivalent power of the eye, t is the fundus object size (4 mm), and s is its measured size on the slit lamp biomicroscope, we calculated the fundus lens correction factor p. 7 Measurements were repeated at a separate session, and the 95% confidence interval for repeatability was calculated. 9 To investigate the change in magnification of the system and the correction factor p with variation in condensing lens position, measurements of the fundus object size were obtained as described when the fundus lens position was altered by Ϯ2 mm relative to the model eye's cornea under myopic and hyperopic conditions. RESULT

Biomicroscopic Measurement of the Optic Disc with a High-Power Positive Lens

PURPOSE. To compare the magnification properties of four different indirect double aspheric fundus examination lenses for clinical disc biometry. METHODS. Experimental study in a model eye. The relationship between the true size of a fundus object and its image was calculated for each fundus lens for an ametropic range between Ϫ12.5 and ϩ12.6 D using a slit lamp biomicroscope with adjustable beam length. RESULTS. Equations for determining the correction factor p (degrees per millimeter) were calculated for each fundus lens. The factor can be used in calculations to determine true optic disc size. The total change in magnification of the system from myopia to hyperopia was Ϫ21.1% to ϩ24.0% (60-D lens; Volk Opticals, Mentor, OH), Ϫ12.9% to ϩ16.2% (Volk super 66 stereo fundus lens), Ϫ13.2% to ϩ13.9% (Volk 78-D lens), and Ϫ13.3% to ϩ14.0% (Volk super-field NC lens). When the fundus lens position was altered im relation to the model eye by Ϯ2 mm under myopic conditions, the change in magnification of the system was Ϫ4.3% to ϩ5.7% (60-D lens), Ϫ4.6% to ϩ6.1% (66 stereo fundus lens), Ϫ4.9% to ϩ6.3% (78-D lens), and Ϫ5.9% to ϩ7.8% (super-field NC lens). In the hyperopic condition the change was Ϫ2.7% to ϩ3.6%, Ϫ3.4% to ϩ4.5%, Ϫ3.6% to ϩ4.8%, and Ϫ4.5% to ϩ6.0%. CONCLUSIONS. The study has shown that the use of a single magnification correction value for each fundus lens may not be appropriate. These findings have important implications for the way in which calculations for determining the true optic disc size and other structures of the posterior pole are performed using indirect biomicroscopy. (Invest Ophthalmol Vis Sci. 2001;42:153-157) I n 1953, El Bayadi 1 first examined the fundus with a planoconvex lens of approximately ϩ60 D using the slit lamp biomicroscope, but the technique was not widely accepted because of aberration and difficulty of use. With the introduction of the double aspheric 60-D lens in 1982 (Volk Opticals, Mentor, OH), the technique started to gain popularity for routine stereoscopic examination of the posterior pole. Since then, many attempts have been made to determine the true size of the optic disc with several types of high-power positive lenses using indirect ophthalmoscopy. 2-7 The advantages of this technique for determining the true optic disc size are the immediate availability of the results and the reduced costs in instruments and personnel compared with sophisticated techniques such as computer-based analysis of optic disc photographs (planimetry), scanning laser ophthalmoscopy, video-ophthalmography, and simultaneous stereo optic disc photography with digital photogrammetry. In addition, only a few ophthalmologists have access to this expensive equipment for routine clinical work, and optic disc measurement is usually performed at the slit lamp biomicroscope. The purpose of this study was to compare four widely used high-power positive lenses regarding their magnification over a wide range of ametropia in the center of the image field, by using a slit lamp biomicroscope with adjustable beam length. MATERIALS AND METHODS Four commercially available double aspheric fundus lenses (60-D lens, 66 stereo fundus lens, 78-D lens, and super-field NC lens) manufactured by Volk Optical and a calibrated slit lamp biomicroscope (HaagStreit 900; Bern-Koeniz, Switzerland) were used for this study. All lenses provide a stereoscopic view of the fundus and a wide field of view. In the slit lamp biomicroscopy the observation system of the slit lamp is focused at a finite, short distance. The light from the fundus exits the eye parallel (i.e., from optical infinity); therefore, the slit lamp cannot be focused on the fundus. With the use of a high-power positive lens, a real inverted image of the fundus is formed in front of the slit lamp biomicroscope (toward the observer). For clear imagery, the slit lamp is focused on this image

Morphologic characteristics of disciform scarring after radiation treatment for age-related macular degeneration

OBJECTIVE: To investigate the influence of radiation therapy on the development of disciform lesions in patients with age-related macular degeneration (AMD). DESIGN: A prospective, nonrandomized, comparative trial (patient self-controlled). PARTICIPANTS: Forty eyes with exudative AMD involving the central fovea in 40 consecutive patients were enrolled in this study. INTERVENTION: Radiation was administered to the posterior pole with an 8-mV photon beam from a linear accelerator. A dose of 14.4 Gy, 1.8 Gy per day, five fractions per week was delivered through a single port. MAIN OUTCOME MEASURES: The visual acuity and the morphologic characteristics, demonstrated by fundus photography, fluorescein, and indocyanine green angiography, were investigated before treatment and every 3 months after treatment over a period of 24 months. In 10 patients with bilateral disease the disciform lesions were compared. RESULTS: Twenty five patients could be followed regularly over the period of 24 months. The disciform lesions occurring after radiation were classified in three types. Type I (10 patients) was characterized by being smaller than 2 DD in size, with little fibrotic tissue underneath the retina, but pronounced retinal pigment epithelial changes. Type II (seven patients) showed extensive growth of the choroidal neovascularization (CNV) extending to and beyond the arcades with angiographically active loops in the peripheral parts. Eight patients had type III lesions develop characterized by a size greater than 2 DD but fewer than 6 DD and by a different amount of fibrotic tissue, hemorrhage, and lipid. Type I scarring was significantly associated with occult CNV without pigment epithelial detachments, whereas type II scarring was associated with classic CNV at the initial presentation (P<0.05). CONCLUSIONS: Although no severe side effects have been reported after radiation therapy for AMD, a subgroup of patients may experience extensive growth of CNV after radiation, causing greater functional damage than occurs spontaneously

Enhanced visualization of macular pathology with the use of ultrahigh resolution optical coherence tomography

Objectives To demonstrate a new generation of ophthalmic optical coherence tomography (OCT) technology with unprecedented axial resolution for enhanced imaging of intraretinal microstructures and to investigate its clinical feasibility to visualize intraretinal morphology of macular pathology. Methods A clinically viable ultrahigh-resolution ophthalmic OCT system was developed and used in clinical imaging for the first time. Fifty-six eyes of 40 selected patients with different macular diseases including macular hole, macular edema, age-related macular degeneration, central serous chorioretinopathy, epiretinal membranes, and detachment of pigment epithelium and sensory retina were included. Outcome Measures Ultrahigh-resolution tomograms visualizing intraretinal morphologic features in different retinal diseases. Results An axial image resolution of approximately