CLINICAL EXAMINATION 73 



before the slit-lamp was devised. The range of magnifications 

 usefully appropriate in slit-lamp examination of the living human 

 eye may be said to be approximately from x 9 to x 45. Clearly, 

 higher magnification is easily possible in other forms of biological 

 work, dependent on the limitations imposed by the intensity of 

 the source of the slit-lamp light, and by the mobility of the object, 

 and by the depth from its surface to the plane under observation. 

 The beginner in clinical examination of the human eye usually 

 makes the mistake of seeking for usefulness in a high magnifica- 

 tion, forgetting that he is thereby limiting himself in focal depth 

 as well as in square dimensions. The endothelial cells in the 

 single layer lining the back of the cornea are just visible as such, 

 by examination of this plane in the axis of its specular reflection, 

 with the X 9 magnification (Fig. 25). Variation of the magnifica- 

 tion is effected by the usual variable combination of oculars and 

 objectives, the standard apparatus being provided with two pairs 

 of oculars and three paired objectives ; for ordinary practical 

 clinical work it suffices to possess one pair of oculars and two 

 paired objectives, affording a x 9 magnification — which just 

 includes the whole cornea within the field of observation — and a 

 X 24 magnification. 



The examination of the lids and conjunctiva presents little 

 or no difficulty. By proximal illumination the blood-corpuscles 

 can be seen circulating in the conjunctival vessels. Sometimes 

 an optical section helps in distinguishing the nature of a cystic 

 swelling of the conjunctiva, e.g., an epithelial implantation or a 

 lymphatic cyst, by revealing the presence or absence of septa 

 within. The rather rare condition of a pigmented mole of the 

 bulbar conjunctiva, close to the limbus (Fig. 43), has a very typical 

 slit-lamp appearance due to the enclosed crypt-like spaces lined 

 by stratified epithelium which are characteristic of this form of 

 overgrowth (7) ; these spaces appear by proximal illumination as 

 multiple dark areas throughout the substance and are far more 

 characteristic than the presence of pigment whose quantity may 

 be so small that it is scarcely detectable clinically. In the very 

 rare instance of this type of overgrowth occurring in the part of 

 the bulbar conjunctiva beneath the upper lid the jDrolonged lid- 



