Methods

The medical records of the 2 eyes of 1175 consecutive patients with pathologic myopia (myopic refractive error > 8 D or axial length ≥ 26.5 mm) who were examined in our High Myopia Clinic from 1996 through 2005 were analyzed. The exclusion criteria were: peak intraocular pressure (IOP) of more than 21 mm Hg, use of antiglaucoma medication at the initial examination, history of optic neuritis or other neuro-ophthalmologic diseases, any type of myopic macular or peripheral lesions that could cause visual field defects such as atrophic or pigmented punched-out chorioretinal lesions; choroidal neovascularization; peripheral chorioretinal lesions; history of vitreoretinal surgery, glaucoma laser surgery, or glaucoma incisional or filtration surgery; and follow-up period of less than 5 years after the initial visit.

The visual fields were examined with the refractive errors corrected by disposable soft contact lenses. The astigmatic refractive errors were corrected by spectacles if they were more than 1 D after wearing soft contact lenses. The Goldmann visual fields were quantified using a grid system similar to that used by Kwon and associates ( Figure 1 ). A grid template was adapted from the visual field scoring system originally described by Esterman. This grid consisted of 100 sectors that lay within the V4 isopter. The grid template was drawn on a transparent piece of paper that was laid over the visual field findings, each sector detected was marked with a dot, and the number of dots that fell in but not on or outside the V4 isopter were counted. The number of dots in the entire area and in the nasal superior, nasal inferior, temporal superior, and temporal inferior quadrants was counted. The same grid template was used for the fellow eye by simply turning it over.

Grid template (for the right eye) used to quantify the Goldmann visual fields. The grid template is made up of 100 sectors that are used to score the visual fields within theV4 isopter of the Goldmann visual field. The visual field is divided into 4 quadrants: superior nasal in blue, superior temporal in red, inferior temporal in green, and the remaining area as inferior nasal. The scale bar is 10 degrees. Adapted from Esterman and Kwon.

The visual field score ranged from 0, a total loss of vision within the V4 isopter, to 100, a full visual field. The final score was expressed as a percentage of the normal field. We considered that eyes with a loss in more than 10 of the sectors or more than 10% of the dots in each field had significant visual field defects. Patients who already had significant visual field defects at the initial examination were excluded. The defects in the visual field were quantified for the entire visual field and for each quadrant. There were 19 sectors in the superior nasal quadrant, 14 in the superior temporal, 27 in the inferior temporal, and 40 in the inferior nasal quadrant ( Figure 1 ). The lowest sector along the vertical line was assigned to the inferior temporal quadrant, and the second lowest sector along the vertical line was assigned to the inferior nasal quadrant ( Figure 1 ).

All patients underwent a complete ophthalmic evaluation, including manifest refractive error (spherical equivalent), best-corrected visual acuity, visual fields with a Goldmann perimeter, IOP measurements with Goldmann applanation tonometer, and detailed ophthalmoscopic examinations. The IOP measurements were made between 2:00 pm and 5:00 pm in all patients. The axial length of the eye was measured by A-scan ultrasonography (Ultrascan; Alcon, Fort Worth, Texas, USA) at least 10 times for each eye, and the average value was used for the statistical analyses. Before each recording, the A-scan Ultrascan was calibrated for accuracy against a standard length. For each ultrasonographic measurement, we confirmed the presence of 4 sharp spikes corresponding to the surface of the cornea, the front and back surfaces of the lens, and the surface of the retina.

The type of posterior staphyloma was determined by its location and was classified by binocular stereoscopic ophthalmoscopy. The staphylomas were classified into 10 types: types I through V were primary staphylomas, and types IV through X were compound staphylomas ( Figure 2 ). We paid special attention to any abrupt changes in the scleral curvature temporal to the optic disc because our early observations suggested that these abrupt changes may be related to the visual field defects. An abrupt change of scleral curvature temporal to the optic disc was observed in all eyes with type VII and IX staphylomas ( Figure 2 ). The determination of a posterior staphyloma was based on a complete agreement of 3 of the authors (K.O.-M., N.S., M.M.).

Drawings of the fundus illustrating the classification of (Left) type VII and (Right) type IX posterior staphyloma by Curtin. Note that there are steps in the scleral curvature temporal to the optic disc in type VII and type IX staphylomas as indicated by arrows.

We also analyzed the shape and orientation of the optic disc. The ovalness of the disc was determined by calculating the ratio of the maximum diameter to the minimum diameter (Mx/Mn ratio; Figure 3 ). When the Mx/Mn ratio of the optic disc was more than 1.5, the optic disc was defined as an oval disc, and a disc with an Mx/Mn ratio of 1.5 or less was defined as a round disc. The oval discs were subdivided into vertically oval, with the major axis ± 10 degrees of the vertical meridian; horizontally oval, with the major axis ± 20 degrees of the horizontal meridian; and obliquely oval, with the major axis between 11 and 69 degrees.

Calculation of the ovalness of the optic disc. When the ratio of the maximum (Max) diameter to the minimum (Min) diameter (Mx/Mn ratio) of the optic disc is more than 1.5, the optic disc is defined as an oval disc. The angle formed by the major axis from the vertical meridian (yellow line) is α. The oval discs are subdivided into those whose major axis is within ± 10 degrees of the vertical meridian, or whose major axis is within ± 20 degrees of the horizontal meridian. Those classified with an oblique included all others.

Magnetic resonance imaging was performed on the patients who agreed to have this examination to rule out the presence of intracranial lesions.

Results

From the 2 eyes of 1175 patients, 1858 eyes were excluded: 1269 eyes because their follow-up period was less than 5.0 years; 281 eyes that already had significant visual field defects at the initial examination; 20 eyes that were being treated with antiglaucoma medication at the initial examination; 18 eyes that had severe cataracts that prevented a detailed observation of the optic disc; 149 eyes for a choroidal neovascularization; and 52 eyes with other retinal pathologic features, for example, chorioretinal atrophy and retinal detachments, that could cause visual field defects. In addition, 43 eyes were excluded because of the presence of peripheral pigmentary changes mimicking retinitis pigmentosa, and 15 eyes because of visual field defects resulting from the presence of a brain infarction. Eleven eyes were excluded because of prior vitreoretinal surgery.

In the end, 492 eyes of 308 patients with high myopia met our inclusion criteria. There were 122 men (204 eyes) and 186 women (288 eyes). The mean age ± standard deviation (SD) was 40.6 ± 16.6 years (range, 8 to 78 years). The mean refractive error ± SD was −13.4 ± 4.1 D (range, −8.25 to −30.0 D), and the mean axial length ± SD was 28.6 ± 1.7 mm (range, 26.6 to 33.0 mm). The mean IOP ± SD at entry was 14.7 ± 2.4 mm Hg (range, 8 to 21 mm Hg). Among the 492 eyes, in 65 eyes (13.2%) of 44 patients, significant visual field defects developed: loss of sensitivity in 10% or more of the sectors in 1 or more quadrants, during a mean follow-up ± SD of 11.6 ± 5.5 years (range, 6 to 30 years). Significant visual field defects were detected in the superior temporal field in 52 eyes, in the inferior temporal field in 42 eyes, in the superior nasal field in 42 eyes, and in the inferior nasal field in 37 eyes. One eye had a change in 2 quadrants, 13 eyes had a change in 3 quadrants, and 33 eyes had a change in 4 quadrants. All of the 44 patients received antiglaucoma medication after the development of significant visual field defects. The average number of medications ± SD during the follow-up was 1.2 ± 0.4 (range, 1 to 3). Magnetic resonance imaging scans, obtained within ± 1 month after the development of VF defects, were available in the medical records of 25 of the 44 (56.8%) patients, and none of them showed a presence of intracranial lesion that would have caused the visual field defect.

Among the 492 eyes, the optic disc was round in 322 eyes (65.4%) and oval in 170 eyes (34.6%). In the 170 eyes with oval optic discs, 84 eyes were vertically oval, 8 were horizontally oval, and 78 eyes were obliquely oval. The correlations between the optic disc shape and visual field defects are shown in Table 1 . In the 427 eyes without significant visual field defects, the round disc type was found significantly more frequently than the oval disc type, whereas in the 65 eyes with significant visual field defects, the oval disc was found significantly more frequently than the round disc ( P < .0001, chi-square test).

The incidence and the sites of the visual field defect in eyes with different optic disc shapes are shown in Table 2 . Because there were only 8 eyes with a horizontally oval optic disc, this type was not analyzed further. Among the eyes with significant visual field defects, 53.8% of the eyes with round optic discs, 65.0% of the eyes with vertically oval discs, and 52.6% of the eyes with obliquely oval discs had both temporal and nasal visual field defects, and the visual fields had a gourd-like shape ( Figure 4 ).

Gourd-shaped visual field in the right eye of a 51-year-old man with a refractive error of −14.5 diopters and an axial length of 30.6 mm. The intraocular pressure (IOP) was 12 mm Hg. (Top) The optic disc is vertically oval, and a vertical ridge can be seen temporal to the optic disc (arrows). A type IX staphyloma is present. (Bottom) Goldmann visual field showing the visual field defects in the temporal and nasal area giving the visual field a gourd-like appearance. The grid score is 68.

Next, we analyzed the factors that may be associated significantly with the visual field defects in eyes with an oval disc ( Table 3 ). A comparison of the clinical characteristics between eyes with and without visual field defects showed that the patients with visual field defects were significantly older, had significantly higher IOPs, had more oval optic discs, and more frequently had an abrupt change of scleral curvature temporal to the optic disc at the time when the visual field defect developed. The results of multiple regression analysis supported these results ( Table 4 ).

TABLE 3

Correlation of Various Factors with Significant Visual Field Defects in Highly Myopic Eyes with Oval Disc Shape

Factors at the Development of Visual Field Defects	Without Visual Field Defect (123 Eyes)	With Visual Field Defect (39 Eyes)	P Value
Age (years)	43.7 ± 15.3	52.7 ± 14.9	.006 a
Refractive error (D)	−14.9 ± 4.8	−14.5 ± 4.5	NS
Axial length (mm)	29.1 ± 1.9	29.1 ± 1.5	NS
Intraocular pressure (mm Hg)	14.4 ± 2.5	15.7 ± 2.4	.006 a
Ratio of maximum to minimum diameter of the optic disc	1.6 ± 0.4 (1.2 to 3.0)	2.0 ± 0.5 (1.5 to 4.0)	< .001 a
Sudden change of scleral curvature temporal to optic disc	19/123	14/39	.01 b

D = diopters, NS = not significant.

Data are presented as mean ± standard deviation (range) or number/total.

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