The document provides design details for a portable slit lamp, including: 1) A parts list and prices for components of the optical system and adjustable clamp. 2) Instructions for assembling the adjustable clamp and optical system, which includes lenses, a prism tower, and slit selector. 3) Diagrams and descriptions of the optical system, slit selector (discrete and continuous options), and base design. 4) Notes on electric components, including reducing the battery voltage for the flashlight and addressing poor electrical connections.

1. Portable slit lamp design manual
Prepared for portable slit lamp project
from Kellogg Eye Center
Any further questions please contact Jingxi Lu,
lujingxi@umich.edu

2. No. Part number Quantity Price Total price
1 base-bot 1 3DP
2 [NUT]M4X2.2MM_90695A035 3 $0.02 $0.06
3 topscrew-96016A117 1 $0.54 $0.54
4 eyebrow rest 1 3DP
5 4Xlens-8539T65 1 $14.56 $14.56
6 prismtower 1 3DP
7 object_cylinder 1 3DP
8 guideway 1 3DP
9 M3x90353A152 3 $0.06 $0.17
10 aperture-middle-width 1 3DP
11 aperture-bot-filter 1 3DP
12 flash light 1 $8.84 $8.84
13 M3.5X20CM_91800A193 2 $0.18 $0.37
14 aperture-top-length 1 3DP
15 slit_selector_cover-bot-1 1 3DP
16 slit_selector_cover-top 1 3DP
17 slit_selector_cover-bot-2 1 3DP
18 2-way-mirror 1 NA
19 M4X18MM_90116A215 4 $0.19 $0.78
20 battery 1 $25.99 $25.99
21 phoneclamp-left 1 3DP
22 clampphone-top 1 3DP
23 spring-94135K8 1 $1.19 $1.19
24 M5X100MM_92010A370 2 $1.31 $2.62
25 clampphone-bot 1 3DP
26 base-top 1 3DP
27 phoneclamp-right 1 3DP
28 M4X55CM_92005A242 1 $0.19 $0.19
29 Wingnut_M4_94300A310 1 $0.17 $0.17
30 M4X40CM_92005A236 1 $0.08 $0.08
31 7Xlens-8539T34 1 $14.56 $14.56
BOM for all parts

3. Smart device (iPhone,
iTouch, Samsung etc.)
Adjustable clamp
Removable chinrest (optional)
Battery
Portable slit lamp for smart devices
Optical system
Base

4. Adjustable clamp
• Suggested clamp width: 5-8 cm
• The adjustable clamp adjusts both the vertical and horizontal axes of the smart device
so its camera center axis can be aligned with the magnifier lens axis.
• When using, clamp the smart device (phone) first and align its horizontal position,
then untighten the wingnut a little bit to align its vertical position. At the end tighten
the wingnut again to make sure the phone doesn’t drop.
• When assembling the spring, fix one end first with M4 screw, then use a thin wire to
pull the other end of spring to a point where another M4 screw can be inserted.
Long bolts prevent
clamp tilting (they are
more robust than 3D
printed plastic rods).
Insert this cylinder
into slit lamp base.
Extension spring for
clamping smart devices

5. Adjustable clamp: assembling procedures
When assembling the spring, fix one end first with M4 screw, then use a thin wire to pull the other
end of spring to a point where another M4 screw can be inserted.
Pull with thin wireSmall opening below

6. Acrylic mirror
Prism tower
7X magnifier lens (inside)
Object cylinder
Slit selector
Flash light (inside)
Two M3 slot screw, 20 mm
Optical system: overall picture
Two M4 cross screw, 18 mm
Cut the acrylic mirror to desired size (9 x 14 mm) and
sand polish the edges. Make sure it can be pressed into
the prism tower tightly.

7. Optical system: assembling procedures
1* 2 3 4 5 6 7 8
9 10 11 12 13 14
• At 1st step use tape to fix these two parts temporary. Keep adjusting the height the of optical
system to make sure the center of light beam is in the center view.
• The guideway (purple part) is only shown in the 1st step. However it must be assembled first

8. Optical system: overall picture
• Measured object distance: 64 mm, Image
distance 80 mm.
• Distance between camera and focus point:
89.5 mm
• Focal length of 4X magnifier lens: 58.5 mm
• > 8X total magnification ratio (4x from
camera)
Removable handle

9. Slit selector, discrete (current version)
Length selector
Width selector
Filter selector
The size of light beam is larger than that of slit itself. The ratio is about 1.25 (image
distance/object distance = 80/64 = 1.25 ) . Based on this ratio the size of slit can be
determined.
Clean the thinnest slit
with thin paper only!
Make sure the gap between
two pairs of slit selector are
as close as possible
(0.5~1mm is acceptable).
Otherwise the light beam
image may not have sharp
edges.

10. Slit selector, continuous (optional version)
Part name Description Quantity Price Total price
flash light
Ultrafire® Cree 7W 300LM Mini LED One Mode
Flashlight
1 $8.84 $8.84
middleplate 2 3DP
RACK
Molded Nylon 14-1/2 Degree Angle
Spur Gear, Rack, 48 Pitch, 1/8"
Face Width, 1/8" Overall Height, 1'
Long
4 $4.78 <$1
rackbase 2 3DP
cover-bot 1 3DP
cover-top 1 3DP
Left GEAR
Molded Nylon 14-1/2 Degree Angle
Spur Gear, 48 Pitch, 20 Teeth, 0.417"
Pitch Diameter, 1/8" Bore, 3/8” O’all
length, 1/8” face width
2 $4.09 $8.18
Right GEAR Same as “Left GEAR” 2 $4.09 $8.18
90353A152
Metric Pan Head Slotted Machine Screw. Zinc-
Plated Steel, M3 Size, 35mm Length, .5mm Pitch
4 $0.06 $0.23
90695A033
Class 04 Steel Thin Hex Nut - DIN 439B
Zinc Plated, M3x0.5 Thread Size, 5.5mm Wide,
1.8mm High
4 $0.03 $0.12
All parts can be found in
gearbox-subassembly.rar

11. Optical system: slit selector, continuous
• Two pairs of gears & rack are used. Each pair of them is in charge
of the adjustment of width or length.
• Use M3 bolts as axes for gears can prevent axes break, which is a
common failure mode when the axes were 3D printed.
• Leave 0.25mm gap between frictional parts (such as gate and base)
can prevent excessive friction force.
Flash light
Make sure the gap between
two pairs of gates are as close
as possible (1mm is acceptable).
Otherwise the light beam
image may not have sharp
edges.
The drawback of this design is
the slit edges might not be
parallel.

12. Base design
• The handle should be removable so that the whole device is more portable
• Make sure there is enough space between handle and slit box (about
100mm long, 15mm wide will be acceptable)
• Add supporting ridge to make the handle stiffer
• Openings for electric wires are necessary
• Openings for adjustable chinrest subassembly

13. Electric components
• The output voltage of batter is 5V, which is too high for the flash light.
Potential failure modes due to high input voltage include:
1. at first the light intensity is very strong and flashlight becomes overheat
2. light becomes dim after a while
3. flashlight turns off automatically in 10 sec.
The working voltage and current for the flashlight are about 1.5V and 200mA
• Current solution for reducing the input voltage is to use 15 Ω resistor.
However the disadvantages are: the input voltage on flashlight drops to 0.8 V,
and the considerable amount of heat generated by resistors reduces the energy
efficiency of the device quite significantly.
• Another severe failure mode is the poor electric connection. Since the optical
system moves all the time when using, if the wire pins hit any obstacles, the
circuit breaks very easily. Need to solve this problem in the future.

14. Some real pictures