PREVALENCE OF LATTICE DEGENERATION IN AXIAL MYOPIA

Lattice degeneration is an important predisposing factor for retinal detachment. A cross sectional study of 221 patients and 405 eyes with axial myopia of 25mm (–3.oo diopters) or more, was conducted with an objective to find out prevalence of lattice degeneration of the retina among them. Of 221 patients, 48 (21.7%) had the lattice degeneration consisting of 35 uniocular (72.9%) and 13 binocular patients (27.1%). Of 139 males, 36 (25.89%) had lattice degeneration; of 82 females, 12 (14.63%) had lattice degeneration (RR=1.26; 95%CI=1.03-1.55; p=0.049). Axial length was from 25mm to 35.77mm (mean=27.63mm, SD 1.98). The greatest prevalence of lattice degeneration.9% (16 of 73 eyes) was found in eyes with axial length of 26mm to 26.99 mm (-6.0D to –8.97.0D), and the least incidence was 8.6% (8 of 93 eyes) in eyes with axial length 25mm to 25.99 mm (-3.0 D to –5.97.0 D). Over all prevalence of lattice degeneration was 15% (61 of 405 eyes) of eye(s) with axial length of 25 mm (-3.0 D) or more. In the age groups below 40 years, the prevalence of lattice degeneration was highest 85.24% (59 of 61 eyes). The lattice degeneration of retina is more prevalent in males of age less than 40 years with moderate axial myopia.


INTRODUCTION
Lattice degeneration of the retina is an important retinal abnormality, which is related to the retinal detachment (RD).The pathogenesis of lattice degeneration is still not well understand.However, the important mechanisms, which plays role in development of lattice degeneration are developmental, degenerative (abiotrophic) and ischemic (retinal and choroidal) process. 1 Typical lattice lesions are sharply defined circumferentially oriented areas of retinal thinning located anterior to the fundus equator. 2 A fishbone or crosshatched pattern of sclerotic, white retinal arterioles and venules within the base of the lattice degeneration are a frequent finding. 3owever, it can be present in association with other several clinical features like localized round, oval, or linear retinal thinning; pigmentation; whitish yellow surface flecks; round, oval, or linear red craters; small atrophic round holes; branching white lines, yellow atrophic spots and rarely tractional tears at the ends or posterior margins of the lesion, which are the frequent cause of retinal detachment. 4The estimated prevalence of lattice degeneration is 6% -8% of the general population 1,5 and the incidence is higher in individuals older than 10 years 6 and in myopic eyes. 7However it is not restricted to eyes with myopia as it was found in emmetropic cases (4.5%) 8 and in hyperopic or emmetropic eyes (25%) 8 Hyams and Newmann 8 reported a 15% incidence of lattice degeneration in 332 eyes with more than one diopter of myopia.Lattice degeneration is present in approximately 20% of patients with RD 9 and in fellow eyes of phakic RD. 10 The prevalence of lattice lesion was found to increase directly with increasing axial length in study by Karline and Curtin, 11 whereas reverse was true in the study by Celorio and Pruett. 12

OBJECTIVE
Study the prevalence of lattice degeneration in axial myopia.

PATIENTS AND METHODS
This prospective study was carried out in retina clinic of Shree Rana Ambika Shah Eye Hospital in Bhairahawa, over a period of February 2003 to January 2004.All patients with axial myopia of 25mm and more, and the patients not mentioned in exclusion criteria, were included in this study.Cases excluded in this study were: eyes having poor visibility of fundus due to hazy ocular media (Corneal opacity, dense cataract, vitreous hemorrhage or opacities), myopia related with other ocular pathology (retinitis pigmentosa, retinopathy of prematurity, retinal detachment surgery), nonaxial myopia (corneal or lenticular), enophthalmos (scleral depression is poor) and recent intra-ocular operative cases (those who are not suitable for scleral depression due to risk of wound opening).All myopic cases were referred from general out patient door clinic to the retina clinic for evaluation.All included (consecutive) cases underwent anterior segment examination with slit lamp followed by fundus evaluation only in well-dilated eyes after counseling for good cooperation and scleral depression and with Goldman Three-mirror contact lens.Examination was performed without general anesthesia.Axial length was measured only with A-scan (contact method) for study and one highest reading was taken.Ultrasonography (USG B scan) was used in those cases having posterior staphyloma (to locate and measure it) followed by A-scan for more accurate reading.The parameters recorded after completing the examination were: demography, age, gender, axial length in mm (A-scan), presence of lattice degeneration and it's type, location, orientation and extent, presence of retinal breaks and retinal detachment.Above data was analyzed using general statistical tool.

DISCUSSION
Several studies have been done to show the prevalence of lattice degeneration in axial myopia and this study has similar results in many aspects.Over all in our study, the prevalence of lattice degeneration was 15% (61 of 405 eyes) of eye(s) with axial length of 25 mm (-3.0 D) or more, which was less than that of Celerio and Prutte 12 and Cambiaggi 15 et al ((24.1% and 20% respectively) in myopia of 6.0 D or more.The present study also showed that males were affected by lattice degeneration more than females (3:1 ratio) in contrast to Celorio and Prutte, where females were more commonly affected.Our finding of 42.62% (26 of 61 eyes) bilaterally affected was similar to the results of Celorio et all (45.8%),Karlin et al (40%), Byer 6 (34%) and Shiomi 16 (31.6%).Most of the lattice lesion (70.49%) in our study was found in temporal area and it was similar to Celorio (89.5%).Pigmented lattice was more common (82%) 17  Similar results of higher prevalence of lattice degeneration, was observed by others 18,19 too in myopia of axial length 25 mm to 27 mm (-3 to -10.0 D).
In contrast to the results of Shiomis' and Celorio (Fig. 1), our study showed tendency of decreasing lattice with increasing axial length only in myopia of more than -15.0 D (Fig. 2).It can be explained, on the basis of Yuras 20 finding, that in high myopic eyes with posterior staphyloma, the lattice is significantly less than the entirely elongated eyes.The other factor is that lattice degeneration may be more closely linked genetically with mild (physiologic) than with severe (pathologic) myopia.
Smith and associates 21 observed in 3065 consecutive postoperative eyes and found 6.3% prevalence of retinal detachment in moderate myopic -3 D to -7.50 D (25 to 26.5 mm axial length) and for severely myopic greater than -7.5 D, it was 4.8%.However, the incidence of retinal detachment is nearly double 22 after clear lens extraction for high myopia greater than -10 D.

CONCLUSION
Overall prevalence of lattice degeneration was 15% in the eye (s) with axial length of 25 mm or more and males of age less than 40 years with moderate axial myopia, were affected predominantly.

Table III : Presence of Lattice According to the Gender Distribution
in occurrence and it was predominantly (49.1%) found in our study too.Most frequently affected age groups by lattice (51 of 160 cases) in Celorio were 21 to 40